listen(String in) {
+ ...
+ return MessageBuilder.withPayload(in.toUpperCase())
+ .setHeader(MessageHeaders.CONTENT_TYPE, "application/xml")
+ .build();
+}
+```
+
+This content type will be passed in the `MessageProperties` to the converter.
+By default, for backwards compatibility, any content type property set by the converter will be overwritten by this value after conversion.
+If you wish to override that behavior, also set the `AmqpHeaders.CONTENT_TYPE_CONVERTER_WINS` to `true` and any value set by the converter will be retained.
+
+###### Multi-method Listeners
+
+Starting with version 1.5.0, you can specify the `@RabbitListener` annotation at the class level.
+Together with the new `@RabbitHandler` annotation, this lets a single listener invoke different methods, based on
+the payload type of the incoming message.
+This is best described using an example:
+
+```
+@RabbitListener(id="multi", queues = "someQueue")
+@SendTo("my.reply.queue")
+public class MultiListenerBean {
+
+ @RabbitHandler
+ public String thing2(Thing2 thing2) {
+ ...
+ }
+
+ @RabbitHandler
+ public String cat(Cat cat) {
+ ...
+ }
+
+ @RabbitHandler
+ public String hat(@Header("amqp_receivedRoutingKey") String rk, @Payload Hat hat) {
+ ...
+ }
+
+ @RabbitHandler(isDefault = true)
+ public String defaultMethod(Object object) {
+ ...
+ }
+
+}
+```
+
+In this case, the individual `@RabbitHandler` methods are invoked if the converted payload is a `Thing2`, a `Cat`, or a `Hat`.
+You should understand that the system must be able to identify a unique method based on the payload type.
+The type is checked for assignability to a single parameter that has no annotations or that is annotated with the `@Payload` annotation.
+Notice that the same method signatures apply, as discussed in the method-level `@RabbitListener` ([described earlier](#message-listener-adapter)).
+
+Starting with version 2.0.3, a `@RabbitHandler` method can be designated as the default method, which is invoked if there is no match on other methods.
+At most, one method can be so designated.
+
+| |`@RabbitHandler` is intended only for processing message payloads after conversion, if you wish to receive the unconverted raw `Message` object, you must use `@RabbitListener` on the method, not the class.|
+|---|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+
+###### `@Repeatable` `@RabbitListener`
+
+Starting with version 1.6, the `@RabbitListener` annotation is marked with `@Repeatable`.
+This means that the annotation can appear on the same annotated element (method or class) multiple times.
+In this case, a separate listener container is created for each annotation, each of which invokes the same listener`@Bean`.
+Repeatable annotations can be used with Java 8 or above.
+
+###### Proxy `@RabbitListener` and Generics
+
+If your service is intended to be proxied (for example, in the case of `@Transactional`), you should keep in mind some considerations when
+the interface has generic parameters.
+Consider the following example:
+
+```
+interface TxService {
+
+ String handle(P payload, String header);
+
+}
+
+static class TxServiceImpl implements TxService {
+
+ @Override
+ @RabbitListener(...)
+ public String handle(Thing thing, String rk) {
+ ...
+ }
+
+}
+```
+
+With a generic interface and a particular implementation, you are forced to switch to the CGLIB target class proxy because the actual implementation of the interface`handle` method is a bridge method.
+In the case of transaction management, the use of CGLIB is configured by using
+an annotation option: `@EnableTransactionManagement(proxyTargetClass = true)`.
+And in this case, all annotations have to be declared on the target method in the implementation, as the following example shows:
+
+```
+static class TxServiceImpl implements TxService {
+
+ @Override
+ @Transactional
+ @RabbitListener(...)
+ public String handle(@Payload Foo foo, @Header("amqp_receivedRoutingKey") String rk) {
+ ...
+ }
+
+}
+```
+
+###### Handling Exceptions
+
+By default, if an annotated listener method throws an exception, it is thrown to the container and the message are requeued and redelivered, discarded, or routed to a dead letter exchange, depending on the container and broker configuration.
+Nothing is returned to the sender.
+
+Starting with version 2.0, the `@RabbitListener` annotation has two new attributes: `errorHandler` and `returnExceptions`.
+
+These are not configured by default.
+
+You can use the `errorHandler` to provide the bean name of a `RabbitListenerErrorHandler` implementation.
+This functional interface has one method, as follows:
+
+```
+@FunctionalInterface
+public interface RabbitListenerErrorHandler {
+
+ Object handleError(Message amqpMessage, org.springframework.messaging.Message message,
+ ListenerExecutionFailedException exception) throws Exception;
+
+}
+```
+
+As you can see, you have access to the raw message received from the container, the spring-messaging `Message` object produced by the message converter, and the exception that was thrown by the listener (wrapped in a `ListenerExecutionFailedException`).
+The error handler can either return some result (which is sent as the reply) or throw the original or a new exception (which is thrown to the container or returned to the sender, depending on the `returnExceptions` setting).
+
+The `returnExceptions` attribute, when `true`, causes exceptions to be returned to the sender.
+The exception is wrapped in a `RemoteInvocationResult` object.
+On the sender side, there is an available `RemoteInvocationAwareMessageConverterAdapter`, which, if configured into the `RabbitTemplate`, re-throws the server-side exception, wrapped in an `AmqpRemoteException`.
+The stack trace of the server exception is synthesized by merging the server and client stack traces.
+
+| |This mechanism generally works only with the default `SimpleMessageConverter`, which uses Java serialization.` to be registered with the context with the group name.
+
+##### @RabbitListener with Batching
+
+When receiving a [a batch](#template-batching) of messages, the de-batching is normally performed by the container and the listener is invoked with one message at at time.
+Starting with version 2.2, you can configure the listener container factory and listener to receive the entire batch in one call, simply set the factory’s `batchListener` property, and make the method payload parameter a `List`:
+
+```
+@Bean
+public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
+ SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
+ factory.setConnectionFactory(connectionFactory());
+ factory.setBatchListener(true);
+ return factory;
+}
+
+@RabbitListener(queues = "batch.1")
+public void listen1(List in) {
+ ...
+}
+
+// or
+
+@RabbitListener(queues = "batch.2")
+public void listen2(List> in) {
+ ...
+}
+```
+
+Setting the `batchListener` property to true automatically turns off the `deBatchingEnabled` container property in containers that the factory creates (unless `consumerBatchEnabled` is `true` - see below). Effectively, the debatching is moved from the container to the listener adapter and the adapter creates the list that is passed to the listener.
+
+A batch-enabled factory cannot be used with a [multi-method listener](#annotation-method-selection).
+
+Also starting with version 2.2. when receiving batched messages one-at-a-time, the last message contains a boolean header set to `true`.
+This header can be obtained by adding the `@Header(AmqpHeaders.LAST_IN_BATCH)` boolean last` parameter to your listener method.
+The header is mapped from `MessageProperties.isLastInBatch()`.
+In addition, `AmqpHeaders.BATCH_SIZE` is populated with the size of the batch in every message fragment.
+
+In addition, a new property `consumerBatchEnabled` has been added to the `SimpleMessageListenerContainer`.
+When this is true, the container will create a batch of messages, up to `batchSize`; a partial batch is delivered if `receiveTimeout` elapses with no new messages arriving.
+If a producer-created batch is received, it is debatched and added to the consumer-side batch; therefore the actual number of messages delivered may exceed `batchSize`, which represents the number of messages received from the broker.`deBatchingEnabled` must be true when `consumerBatchEnabled` is true; the container factory will enforce this requirement.
+
+```
+@Bean
+public SimpleRabbitListenerContainerFactory consumerBatchContainerFactory() {
+ SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
+ factory.setConnectionFactory(rabbitConnectionFactory());
+ factory.setConsumerTagStrategy(consumerTagStrategy());
+ factory.setBatchListener(true); // configures a BatchMessageListenerAdapter
+ factory.setBatchSize(2);
+ factory.setConsumerBatchEnabled(true);
+ return factory;
+}
+```
+
+When using `consumerBatchEnabled` with `@RabbitListener`:
+
+```
+@RabbitListener(queues = "batch.1", containerFactory = "consumerBatchContainerFactory")
+public void consumerBatch1(List amqpMessages) {
+ this.amqpMessagesReceived = amqpMessages;
+ this.batch1Latch.countDown();
+}
+
+@RabbitListener(queues = "batch.2", containerFactory = "consumerBatchContainerFactory")
+public void consumerBatch2(List> messages) {
+ this.messagingMessagesReceived = messages;
+ this.batch2Latch.countDown();
+}
+
+@RabbitListener(queues = "batch.3", containerFactory = "consumerBatchContainerFactory")
+public void consumerBatch3(List strings) {
+ this.batch3Strings = strings;
+ this.batch3Latch.countDown();
+}
+```
+
+* the first is called with the raw, unconverted `org.springframework.amqp.core.Message` s received.
+
+* the second is called with the `org.springframework.messaging.Message` s with converted payloads and mapped headers/properties.
+
+* the third is called with the converted payloads, with no access to headers/properteis.
+
+You can also add a `Channel` parameter, often used when using `MANUAL` ack mode.
+This is not very useful with the third example because you don’t have access to the `delivery_tag` property.
+
+##### Using Container Factories
+
+Listener container factories were introduced to support the `@RabbitListener` and registering containers with the `RabbitListenerEndpointRegistry`, as discussed in [Programmatic Endpoint Registration](#async-annotation-driven-registration).
+
+Starting with version 2.1, they can be used to create any listener container — even a container without a listener (such as for use in Spring Integration).
+Of course, a listener must be added before the container is started.
+
+There are two ways to create such containers:
+
+* Use a SimpleRabbitListenerEndpoint
+
+* Add the listener after creation
+
+The following example shows how to use a `SimpleRabbitListenerEndpoint` to create a listener container:
+
+```
+@Bean
+public SimpleMessageListenerContainer factoryCreatedContainerSimpleListener(
+ SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory) {
+ SimpleRabbitListenerEndpoint endpoint = new SimpleRabbitListenerEndpoint();
+ endpoint.setQueueNames("queue.1");
+ endpoint.setMessageListener(message -> {
+ ...
+ });
+ return rabbitListenerContainerFactory.createListenerContainer(endpoint);
+}
+```
+
+The following example shows how to add the listener after creation:
+
+```
+@Bean
+public SimpleMessageListenerContainer factoryCreatedContainerNoListener(
+ SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory) {
+ SimpleMessageListenerContainer container = rabbitListenerContainerFactory.createListenerContainer();
+ container.setMessageListener(message -> {
+ ...
+ });
+ container.setQueueNames("test.no.listener.yet");
+ return container;
+}
+```
+
+In either case, the listener can also be a `ChannelAwareMessageListener`, since it is now a sub-interface of `MessageListener`.
+
+These techniques are useful if you wish to create several containers with similar properties or use a pre-configured container factory such as the one provided by Spring Boot auto configuration or both.
+
+| |Containers created this way are normal `@Bean` instances and are not registered in the `RabbitListenerEndpointRegistry`.|
+|---|------------------------------------------------------------------------------------------------------------------------|
+
+##### Asynchronous `@RabbitListener` Return Types
+
+Starting with version 2.1, `@RabbitListener` (and `@RabbitHandler`) methods can be specified with asynchronous return types `ListenableFuture` and `Mono`, letting the reply be sent asynchronously.
+
+| |The listener container factory must be configured with `AcknowledgeMode.MANUAL` so that the consumer thread will not ack the message; instead, the asynchronous completion will ack or nack the message when the async operation completes.
+
+```
+
+```
+@Bean
+public SimpleMessageListenerContainer(ConnectionFactory connectionFactory) {
+ SimpleMessageListenerContainer container = new SimpleMessageListenerContainer(connectionFactory);
+ ...
+ container.setIdleEventInterval(60000L);
+ ...
+ return container;
+}
+```
+
+```
+@Bean
+public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
+ SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
+ factory.setConnectionFactory(rabbitConnectionFactory());
+ factory.setIdleEventInterval(60000L);
+ ...
+ return factory;
+}
+```
+
+In each of these cases, an event is published once per minute while the container is idle.
+
+###### Event Consumption
+
+You can capture idle events by implementing `ApplicationListener` — either a general listener, or one narrowed to only
+receive this specific event.
+You can also use `@EventListener`, introduced in Spring Framework 4.2.
+
+The following example combines the `@RabbitListener` and `@EventListener` into a single class.
+You need to understand that the application listener gets events for all containers, so you may need to
+check the listener ID if you want to take specific action based on which container is idle.
+You can also use the `@EventListener` `condition` for this purpose.
+
+The events have four properties:
+
+* `source`: The listener container instance
+
+* `id`: The listener ID (or container bean name)
+
+* `idleTime`: The time the container had been idle when the event was published
+
+* `queueNames`: The names of the queue(s) that the container listens to
+
+The following example shows how to create listeners by using both the `@RabbitListener` and the `@EventListener` annotations:
+
+```
+public class Listener {
+
+ @RabbitListener(id="someId", queues="#{queue.name}")
+ public String listen(String foo) {
+ return foo.toUpperCase();
+ }
+
+ @EventListener(condition = "event.listenerId == 'someId'")
+ public void onApplicationEvent(ListenerContainerIdleEvent event) {
+ ...
+ }
+
+}
+```
+
+| |Event listeners see events for all containers.
+
+
+
+
+
+
+```
+
+As shown above, `Jackson2JsonMessageConverter` uses a `DefaultClassMapper` by default.
+Type information is added to (and retrieved from) `MessageProperties`.
+If an inbound message does not contain type information in `MessageProperties`, but you know the expected type, you
+can configure a static type by using the `defaultType` property, as the following example shows:
+
+```
+
+
+
+
+
+
+```
+
+In addition, you can provide custom mappings from the value in the `*TypeId*` header.
+The following example shows how to do so:
+
+```
+@Bean
+public Jackson2JsonMessageConverter jsonMessageConverter() {
+ Jackson2JsonMessageConverter jsonConverter = new Jackson2JsonMessageConverter();
+ jsonConverter.setClassMapper(classMapper());
+ return jsonConverter;
+}
+
+@Bean
+public DefaultClassMapper classMapper() {
+ DefaultClassMapper classMapper = new DefaultClassMapper();
+ Map> idClassMapping = new HashMap<>();
+ idClassMapping.put("thing1", Thing1.class);
+ idClassMapping.put("thing2", Thing2.class);
+ classMapper.setIdClassMapping(idClassMapping);
+ return classMapper;
+}
+```
+
+Now, if the sending system sets the header to `thing1`, the converter creates a `Thing1` object, and so on.
+See the [Receiving JSON from Non-Spring Applications](#spring-rabbit-json) sample application for a complete discussion about converting messages from non-Spring applications.
+
+###### Converting from a `Message`
+
+Inbound messages are converted to objects according to the type information added to headers by the sending system.
+
+In versions prior to 1.6, if type information is not present, conversion would fail.
+Starting with version 1.6, if type information is missing, the converter converts the JSON by using Jackson defaults (usually a map).
+
+Also, starting with version 1.6, when you use `@RabbitListener` annotations (on methods), the inferred type information is added to the `MessageProperties`.
+This lets the converter convert to the argument type of the target method.
+This only applies if there is one parameter with no annotations or a single parameter with the `@Payload` annotation.
+Parameters of type `Message` are ignored during the analysis.
+
+| |By default, the inferred type information will override the inbound `*TypeId*` and related headers created message) {...}
+
+@RabbitListener
+public void thing1(Thing1 thing1, String bar) {...}
+
+@RabbitListener
+public void thing1(Thing1 thing1, o.s.messaging.Message message) {...}
+```
+
+In the first four cases in the preceding listing, the converter tries to convert to the `Thing1` type.
+The fifth example is invalid because we cannot determine which argument should receive the message payload.
+With the sixth example, the Jackson defaults apply due to the generic type being a `WildcardType`.
+
+You can, however, create a custom converter and use the `targetMethod` message property to decide which type to convert
+the JSON to.
+
+| |This type inference can only be achieved when the `@RabbitListener` annotation is declared at the method level.> thing1 =
+ rabbitTemplate.receiveAndConvert(new ParameterizedTypeReference>>() { });
+```
+
+| |Starting with version 2.1, the `AbstractJsonMessageConverter` class has been removed.
+
+
+
+
+
+```
+
+##### `Jackson2XmlMessageConverter`
+
+This class was introduced in version 2.1 and can be used to convert messages from and to XML.
+
+Both `Jackson2XmlMessageConverter` and `Jackson2JsonMessageConverter` have the same base class: `AbstractJackson2MessageConverter`.
+
+| |The `AbstractJackson2MessageConverter` class is introduced to replace a removed class: `AbstractJsonMessageConverter`.|
+|---|----------------------------------------------------------------------------------------------------------------------|
+
+The `Jackson2XmlMessageConverter` uses the `com.fasterxml.jackson` 2.x library.
+
+You can use it the same way as `Jackson2JsonMessageConverter`, except it supports XML instead of JSON.
+The following example configures a `Jackson2JsonMessageConverter`:
+
+```
+
+
+
+
+
+
+```
+
+See [Jackson2JsonMessageConverter](#json-message-converter) for more information.
+
+| |Starting with version 2.2, `application/xml` is assumed if there is no `contentType` property, or it has the default value `application/octet-stream`.
+
+
+
+
+
+```
+
+##### Java Deserialization
+
+This section covers how to deserialize Java objects.
+
+| |There is a possible vulnerability when deserializing java objects from untrusted sources..
+Explicitly setting the attribute to `correlationId` is the same as omitting the attribute.
+The client and server must use the same header for correlation data.
+
+| |Spring AMQP version 1.1 used a custom property called `spring_reply_correlation` for this data. sub element.
+This element provides a listener container for the reply queue, with the template being the listener.
+All of the [Message Listener Container Configuration](#containerAttributes) attributes allowed on a \ are allowed on the element, except for `connection-factory` and `message-converter`, which are inherited from the template’s configuration.
+
+| |If you run multiple instances of your application or use multiple `RabbitTemplate` instances, you **MUST** use a unique reply queue for each.
+
+```
+
+While the container and template share a connection factory, they do not share a channel.
+Therefore, requests and replies are not performed within the same transaction (if transactional).
+
+| |Prior to version 1.5.0, the `reply-address` attribute was not available./` and the reply is routed to the specified exchange and routed to a queue bound with the routing key.` must be configured as a separate `` component.`) must refer to the same queue logically.|
+|---|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+
+With this configuration, a `SimpleListenerContainer` is used to receive the replies, with the `RabbitTemplate` being the `MessageListener`.
+When defining a template with the `
+
+
+
+
+
+ future = this.template.convertSendAndReceive("foo");
+
+ // do some more work
+
+ String reply = null;
+ try {
+ reply = future.get();
+ }
+ catch (ExecutionException e) {
+ ...
+ }
+
+ ...
+
+}
+
+public void doSomeWorkAndGetResultAsync() {
+
+ ...
+
+ RabbitConverterFuture future = this.template.convertSendAndReceive("foo");
+ future.addCallback(new ListenableFutureCallback() {
+
+ @Override
+ public void onSuccess(String result) {
+ ...
+ }
+
+ @Override
+ public void onFailure(Throwable ex) {
+ ...
+ }
+
+ });
+
+ ...
+
+}
+```
+
+If `mandatory` is set and the message cannot be delivered, the future throws an `ExecutionException` with a cause of `AmqpMessageReturnedException`, which encapsulates the returned message and information about the return.
+
+If `enableConfirms` is set, the future has a property called `confirm`, which is itself a `ListenableFuture` with `true` indicating a successful publish.
+If the confirm future is `false`, the `RabbitFuture` has a further property called `nackCause`, which contains the reason for the failure, if available.
+
+| |The publisher confirm is discarded if it is received after the reply, since the reply implies a successful publish.|
+|---|-------------------------------------------------------------------------------------------------------------------|
+
+You can set the `receiveTimeout` property on the template to time out replies (it defaults to `30000` - 30 seconds).
+If a timeout occurs, the future is completed with an `AmqpReplyTimeoutException`.
+
+The template implements `SmartLifecycle`.
+Stopping the template while there are pending replies causes the pending `Future` instances to be canceled.
+
+Starting with version 2.0, the asynchronous template now supports [direct reply-to](https://www.rabbitmq.com/direct-reply-to.html) instead of a configured reply queue.
+To enable this feature, use one of the following constructors:
+
+```
+public AsyncRabbitTemplate(ConnectionFactory connectionFactory, String exchange, String routingKey)
+
+public AsyncRabbitTemplate(RabbitTemplate template)
+```
+
+See [RabbitMQ Direct reply-to](#direct-reply-to) to use direct reply-to with the synchronous `RabbitTemplate`.
+
+Version 2.0 introduced variants of these methods (`convertSendAndReceiveAsType`) that take an additional `ParameterizedTypeReference` argument to convert complex returned types.
+You must configure the underlying `RabbitTemplate` with a `SmartMessageConverter`.
+See [Converting From a `Message` With `RabbitTemplate`](#json-complex) for more information.
+
+##### Spring Remoting with AMQP
+
+| |This feature is deprecated and will be removed in 3.0.
+
+
+
+
+
+
+```
+
+```
+
+
+
+
+
+```
+
+| |The `AmqpInvokerServiceExporter` can process only properly formed messages, such as those sent from the `AmqpProxyFactoryBean`.
+
+```
+
+See [Automatic Declaration of Exchanges, Queues, and Bindings](#automatic-declaration).
+
+The RabbitMQ implementation of this interface is `RabbitAdmin`, which, when configured by using Spring XML, resembles the following example:
+
+```
+
+
+
+
+
+
+
+
+
+```
+
+In the preceding example, we use anonymous queues (actually, internally, just queues with names generated by the framework, not by the broker) and refer to them by ID.
+We can also declare queues with explicit names, which also serve as identifiers for their bean definitions in the context.
+The following example configures a queue with an explicit name:
+
+```
+` element.
+The following example shows how to do so:
+
+```
+
+
+
+
+```
+
+By default, the arguments are assumed to be strings.
+For arguments of other types, you must provide the type.
+The following example shows how to specify the type:
+
+```
+
+
+
+
+```
+
+When providing arguments of mixed types, you must provide the type for each entry element.
+The following example shows how to do so:
+
+```
+
+
+
+ 100
+
+
+
+```
+
+With Spring Framework 3.2 and later, this can be declared a little more succinctly, as follows:
+
+```
+
+
+
+
+```
+
+When you use Java configuration, the `Queue.X_QUEUE_LEADER_LOCATOR` argument is supported as a first class property through the `setLeaderLocator()` method on the `Queue` class.
+Starting with version 2.1, anonymous queues are declared with this property set to `client-local` by default.
+This ensures that the queue is declared on the node the application is connected to.
+
+| |The RabbitMQ broker does not allow declaration of a queue with mismatched arguments.
+
+
+
+
+
+
+
+```
+
+Starting with version 1.6, you can configure `Exchanges` with an `internal` flag (defaults to `false`) and such an`Exchange` is properly configured on the Broker through a `RabbitAdmin` (if one is present in the application context).
+If the `internal` flag is `true` for an exchange, RabbitMQ does not let clients use the exchange.
+This is useful for a dead letter exchange or exchange-to-exchange binding, where you do not wish the exchange to be used
+directly by publishers.
+
+To see how to use Java to configure the AMQP infrastructure, look at the Stock sample application,
+where there is the `@Configuration` class `AbstractStockRabbitConfiguration`, which ,in turn has`RabbitClientConfiguration` and `RabbitServerConfiguration` subclasses.
+The following listing shows the code for `AbstractStockRabbitConfiguration`:
+
+```
+@Configuration
+public abstract class AbstractStockAppRabbitConfiguration {
+
+ @Bean
+ public CachingConnectionFactory connectionFactory() {
+ CachingConnectionFactory connectionFactory =
+ new CachingConnectionFactory("localhost");
+ connectionFactory.setUsername("guest");
+ connectionFactory.setPassword("guest");
+ return connectionFactory;
+ }
+
+ @Bean
+ public RabbitTemplate rabbitTemplate() {
+ RabbitTemplate template = new RabbitTemplate(connectionFactory());
+ template.setMessageConverter(jsonMessageConverter());
+ configureRabbitTemplate(template);
+ return template;
+ }
+
+ @Bean
+ public Jackson2JsonMessageConverter jsonMessageConverter() {
+ return new Jackson2JsonMessageConverter();
+ }
+
+ @Bean
+ public TopicExchange marketDataExchange() {
+ return new TopicExchange("app.stock.marketdata");
+ }
+
+ // additional code omitted for brevity
+
+}
+```
+
+In the Stock application, the server is configured by using the following `@Configuration` class:
+
+```
+@Configuration
+public class RabbitServerConfiguration extends AbstractStockAppRabbitConfiguration {
+
+ @Bean
+ public Queue stockRequestQueue() {
+ return new Queue("app.stock.request");
+ }
+}
+```
+
+This is the end of the whole inheritance chain of `@Configuration` classes.
+The end result is that `TopicExchange` and `Queue` are declared to the broker upon application startup.
+There is no binding of `TopicExchange` to a queue in the server configuration, as that is done in the client application.
+The stock request queue, however, is automatically bound to the AMQP default exchange.
+This behavior is defined by the specification.
+
+The client `@Configuration` class is a little more interesting.
+Its declaration follows:
+
+```
+@Configuration
+public class RabbitClientConfiguration extends AbstractStockAppRabbitConfiguration {
+
+ @Value("${stocks.quote.pattern}")
+ private String marketDataRoutingKey;
+
+ @Bean
+ public Queue marketDataQueue() {
+ return amqpAdmin().declareQueue();
+ }
+
+ /**
+ * Binds to the market data exchange.
+ * Interested in any stock quotes
+ * that match its routing key.
+ */
+ @Bean
+ public Binding marketDataBinding() {
+ return BindingBuilder.bind(
+ marketDataQueue()).to(marketDataExchange()).with(marketDataRoutingKey);
+ }
+
+ // additional code omitted for brevity
+
+}
+```
+
+The client declares another queue through the `declareQueue()` method on the `AmqpAdmin`.
+It binds that queue to the market data exchange with a routing pattern that is externalized in a properties file.
+
+##### Builder API for Queues and Exchanges
+
+Version 1.6 introduces a convenient fluent API for configuring `Queue` and `Exchange` objects when using Java configuration.
+The following example shows how to use it:
+
+```
+@Bean
+public Queue queue() {
+ return QueueBuilder.nonDurable("foo")
+ .autoDelete()
+ .exclusive()
+ .withArgument("foo", "bar")
+ .build();
+}
+
+@Bean
+public Exchange exchange() {
+ return ExchangeBuilder.directExchange("foo")
+ .autoDelete()
+ .internal()
+ .withArgument("foo", "bar")
+ .build();
+}
+```
+
+See the Javadoc for [`org.springframework.amqp.core.QueueBuilder`](https://docs.spring.io/spring-amqp/docs/latest-ga/api/org/springframework/amqp/core/QueueBuilder.html) and [`org.springframework.amqp.core.ExchangeBuilder`](https://docs.spring.io/spring-amqp/docs/latest-ga/api/org/springframework/amqp/core/ExchangeBuilder.html) for more information.
+
+Starting with version 2.0, the `ExchangeBuilder` now creates durable exchanges by default, to be consistent with the simple constructors on the individual `AbstractExchange` classes.
+To make a non-durable exchange with the builder, use `.durable(false)` before invoking `.build()`.
+The `durable()` method with no parameter is no longer provided.
+
+Version 2.2 introduced fluent APIs to add "well known" exchange and queue arguments…
+
+```
+@Bean
+public Queue allArgs1() {
+ return QueueBuilder.nonDurable("all.args.1")
+ .ttl(1000)
+ .expires(200_000)
+ .maxLength(42)
+ .maxLengthBytes(10_000)
+ .overflow(Overflow.rejectPublish)
+ .deadLetterExchange("dlx")
+ .deadLetterRoutingKey("dlrk")
+ .maxPriority(4)
+ .lazy()
+ .leaderLocator(LeaderLocator.minLeaders)
+ .singleActiveConsumer()
+ .build();
+}
+
+@Bean
+public DirectExchange ex() {
+ return ExchangeBuilder.directExchange("ex.with.alternate")
+ .durable(true)
+ .alternate("alternate")
+ .build();
+}
+```
+
+##### Declaring Collections of Exchanges, Queues, and Bindings
+
+You can wrap collections of `Declarable` objects (`Queue`, `Exchange`, and `Binding`) in `Declarables` objects.
+The `RabbitAdmin` detects such beans (as well as discrete `Declarable` beans) in the application context, and declares the contained objects on the broker whenever a connection is established (initially and after a connection failure).
+The following example shows how to do so:
+
+```
+@Configuration
+public static class Config {
+
+ @Bean
+ public CachingConnectionFactory cf() {
+ return new CachingConnectionFactory("localhost");
+ }
+
+ @Bean
+ public RabbitAdmin admin(ConnectionFactory cf) {
+ return new RabbitAdmin(cf);
+ }
+
+ @Bean
+ public DirectExchange e1() {
+ return new DirectExchange("e1", false, true);
+ }
+
+ @Bean
+ public Queue q1() {
+ return new Queue("q1", false, false, true);
+ }
+
+ @Bean
+ public Binding b1() {
+ return BindingBuilder.bind(q1()).to(e1()).with("k1");
+ }
+
+ @Bean
+ public Declarables es() {
+ return new Declarables(
+ new DirectExchange("e2", false, true),
+ new DirectExchange("e3", false, true));
+ }
+
+ @Bean
+ public Declarables qs() {
+ return new Declarables(
+ new Queue("q2", false, false, true),
+ new Queue("q3", false, false, true));
+ }
+
+ @Bean
+ @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
+ public Declarables prototypes() {
+ return new Declarables(new Queue(this.prototypeQueueName, false, false, true));
+ }
+
+ @Bean
+ public Declarables bs() {
+ return new Declarables(
+ new Binding("q2", DestinationType.QUEUE, "e2", "k2", null),
+ new Binding("q3", DestinationType.QUEUE, "e3", "k3", null));
+ }
+
+ @Bean
+ public Declarables ds() {
+ return new Declarables(
+ new DirectExchange("e4", false, true),
+ new Queue("q4", false, false, true),
+ new Binding("q4", DestinationType.QUEUE, "e4", "k4", null));
+ }
+
+}
+```
+
+| |In versions prior to 2.1, you could declare multiple `Declarable` instances by defining beans of type `Collection`.
+
+
+
+```
+
+| |By default, the `auto-declare` attribute is `true` and, if the `declared-by` is not supplied (or is empty), then all `RabbitAdmin` instances declare the object (as long as the admin’s `auto-startup` attribute is `true`, the default, and the admin’s `explicit-declarations-only` attribute is false).|
+|---|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+
+Similarly, you can use Java-based `@Configuration` to achieve the same effect.
+In the following example, the components are declared by `admin1` but not by`admin2`:
+
+```
+@Bean
+public RabbitAdmin admin1() {
+ return new RabbitAdmin(cf1());
+}
+
+@Bean
+public RabbitAdmin admin2() {
+ return new RabbitAdmin(cf2());
+}
+
+@Bean
+public Queue queue() {
+ Queue queue = new Queue("foo");
+ queue.setAdminsThatShouldDeclare(admin1());
+ return queue;
+}
+
+@Bean
+public Exchange exchange() {
+ DirectExchange exchange = new DirectExchange("bar");
+ exchange.setAdminsThatShouldDeclare(admin1());
+ return exchange;
+}
+
+@Bean
+public Binding binding() {
+ Binding binding = new Binding("foo", DestinationType.QUEUE, exchange().getName(), "foo", null);
+ binding.setAdminsThatShouldDeclare(admin1());
+ return binding;
+}
+```
+
+##### A Note On the `id` and `name` Attributes
+
+The `name` attribute on `` element
+for a bean reference that implements `AnonymousQueue.NamingStrategy`.
+The following examples show how to specify the naming strategy in various ways:
+
+```
+
+
+```
+
+The first example creates names such as `spring.gen-MRBv9sqISkuCiPfOYfpo4g`.
+The second example creates names with a String representation of a UUID.
+The third example creates names such as `custom.gen-MRBv9sqISkuCiPfOYfpo4g`.
+
+You can also provide your own naming strategy bean.
+
+Starting with version 2.1, anonymous queues are declared with argument `Queue.X_QUEUE_LEADER_LOCATOR` set to `client-local` by default.
+This ensures that the queue is declared on the node to which the application is connected.
+You can revert to the previous behavior by calling `queue.setLeaderLocator(null)` after constructing the instance.
+
+##### Recovering Auto-Delete Declarations
+
+Normally, the `RabbitAdmin` (s) only recover queues/exchanges/bindings that are declared as beans in the application context; if any such declarations are auto-delete, they will be removed by the broker if the connection is lost.
+When the connection is re-established, the admin will redeclare the entities.
+Normally, entities created by calling `admin.declareQueue(…)`, `admin.declareExchange(…)` and `admin.declareBinding(…)` will not be recovered.
+
+Starting with version 2.4, the admin has a new property `redeclareManualDeclarations`; when true, the admin will recover these entities in addition to the beans in the application context.
+
+Recovery of individual declarations will not be performed if `deleteQueue(…)`, `deleteExchange(…)` or `removeBinding(…)` is called.
+Associated bindings are removed from the recoverable entities when queues and exchanges are deleted.
+
+Finally, calling `resetAllManualDeclarations()` will prevent the recovery of any previously declared entities.
+
+#### 4.1.12. Broker Event Listener
+
+When the [Event Exchange Plugin](https://www.rabbitmq.com/event-exchange.html) is enabled, if you add a bean of type `BrokerEventListener` to the application context, it publishes selected broker events as `BrokerEvent` instances, which can be consumed with a normal Spring `ApplicationListener` or `@EventListener` method.
+Events are published by the broker to a topic exchange `amq.rabbitmq.event` with a different routing key for each event type.
+The listener uses event keys, which are used to bind an `AnonymousQueue` to the exchange so the listener receives only selected events.
+Since it is a topic exchange, wildcards can be used (as well as explicitly requesting specific events), as the following example shows:
+
+```
+@Bean
+public BrokerEventListener eventListener() {
+ return new BrokerEventListener(connectionFactory(), "user.deleted", "channel.#", "queue.#");
+}
+```
+
+You can further narrow the received events in individual event listeners, by using normal Spring techniques, as the following example shows:
+
+```
+@EventListener(condition = "event.eventType == 'queue.created'")
+public void listener(BrokerEvent event) {
+ ...
+}
+```
+
+#### 4.1.13. Delayed Message Exchange
+
+Version 1.6 introduces support for the[Delayed Message Exchange Plugin](https://www.rabbitmq.com/blog/2015/04/16/scheduling-messages-with-rabbitmq/)
+
+| |The plugin is currently marked as experimental but has been available for over a year (at the time of writing).` but `Message` is received.
+
+* `java.lang.NoSuchMethodException`: Added in version 1.6.3.
+
+* `java.lang.ClassCastException`: Added in version 1.6.3.
+
+You can configure an instance of this error handler with a `FatalExceptionStrategy` so that users can provide their own rules for conditional message rejection — for example, a delegate implementation to the `BinaryExceptionClassifier` from Spring Retry ([Message Listeners and the Asynchronous Case](#async-listeners)).
+In addition, the `ListenerExecutionFailedException` now has a `failedMessage` property that you can use in the decision.
+If the `FatalExceptionStrategy.isFatal()` method returns `true`, the error handler throws an `AmqpRejectAndDontRequeueException`.
+The default `FatalExceptionStrategy` logs a warning message when an exception is determined to be fatal.
+
+Since version 1.6.3, a convenient way to add user exceptions to the fatal list is to subclass `ConditionalRejectingErrorHandler.DefaultExceptionStrategy` and override the `isUserCauseFatal(Throwable cause)` method to return `true` for fatal exceptions.
+
+A common pattern for handling DLQ messages is to set a `time-to-live` on those messages as well as additional DLQ configuration such that these messages expire and are routed back to the main queue for retry.
+The problem with this technique is that messages that cause fatal exceptions loop forever.
+Starting with version 2.1, the `ConditionalRejectingErrorHandler` detects an `x-death` header on a message that causes a fatal exception to be thrown.
+The message is logged and discarded.
+You can revert to the previous behavior by setting the `discardFatalsWithXDeath` property on the `ConditionalRejectingErrorHandler` to `false`.
+
+| |Starting with version 2.1.9, messages with these fatal exceptions are rejected and NOT requeued by default, even if the container acknowledge mode is MANUAL.
+
+```
+
+##### Transaction Synchronization
+
+Synchronizing a RabbitMQ transaction with some other (e.g. DBMS) transaction provides "Best Effort One Phase Commit" semantics.
+It is possible that the RabbitMQ transaction fails to commit during the after completion phase of transaction synchronization.
+This is logged by the `spring-tx` infrastructure as an error, but no exception is thrown to the calling code.
+Starting with version 2.3.10, you can call `ConnectionUtils.checkAfterCompletion()` after the transaction has committed on the same thread that processed the transaction.
+It will simply return if no exception occurred; otherwise it will throw an `AfterCompletionFailedException` which will have a property representing the synchronization status of the completion.
+
+Enable this feature by calling `ConnectionFactoryUtils.enableAfterCompletionFailureCapture(true)`; this is a global flag and applies to all threads.
+
+#### 4.1.17. Message Listener Container Configuration
+
+There are quite a few options for configuring a `SimpleMessageListenerContainer` (SMLC) and a `DirectMessageListenerContainer` (DMLC) related to transactions and quality of service, and some of them interact with each other.
+Properties that apply to the SMLC, DMLC, or `StreamListenerContainer` (StLC) (see [Using the RabbitMQ Stream Plugin](#stream-support) are indicated by the check mark in the appropriate column.
+See [Choosing a Container](#choose-container) for information to help you decide which container is appropriate for your application.
+
+The following table shows the container property names and their equivalent attribute names (in parentheses) when using the namespace to configure a `` is registered with this name, and the-admin`, the infrastructure is able to determine which admin should declare the queue.
+This will also work with `bindings = @QueueBinding(…)` whereby the exchange and binding will also be declared.
+It will NOT work with `queues`, since that expects the queue(s) to already exist.
+
+On the producer side, a convenient `ConnectionFactoryContextWrapper` class is provided, to make using the `RoutingConnectionFactory` (see [Routing Connection Factory](#routing-connection-factory)) simpler.
+
+As you can see above, a `SimpleRoutingConnectionFactory` bean has been added with routing keys `one`, `two` and `three`.
+There is also a `RabbitTemplate` that uses that factory.
+Here is an example of using that template with the wrapper to route to one of the broker clusters.
+
+```
+@Bean
+public ApplicationRunner runner(RabbitTemplate template, ConnectionFactoryContextWrapper wrapper) {
+ return args -> {
+ wrapper.run("one", () -> template.convertAndSend("q1", "toCluster1"));
+ wrapper.run("two", () -> template.convertAndSend("q2", "toCluster2"));
+ wrapper.run("three", () -> template.convertAndSend("q3", "toCluster3"));
+ };
+}
+```
+
+#### 4.1.23. Debugging
+
+Spring AMQP provides extensive logging, especially at the `DEBUG` level.
+
+If you wish to monitor the AMQP protocol between the application and broker, you can use a tool such as WireShark, which has a plugin to decode the protocol.
+Alternatively, the RabbitMQ Java client comes with a very useful class called `Tracer`.
+When run as a `main`, by default, it listens on port 5673 and connects to port 5672 on localhost.
+You can run it and change your connection factory configuration to connect to port 5673 on localhost.
+It displays the decoded protocol on the console.
+Refer to the `Tracer` Javadoc for more information.
+
+### 4.2. Using the RabbitMQ Stream Plugin
+
+Version 2.4 introduces initial support for the [RabbitMQ Stream Plugin Java Client](https://github.com/rabbitmq/rabbitmq-stream-java-client) for the [RabbitMQ Stream Plugin](https://rabbitmq.com/stream.html).
+
+* `RabbitStreamTemplate`
+
+* `StreamListenerContainer`
+
+#### 4.2.1. Sending Messages
+
+The `RabbitStreamTemplate` provides a subset of the `RabbitTemplate` (AMQP) functionality.
+
+Example 1. RabbitStreamOperations
+
+```
+public interface RabbitStreamOperations extends AutoCloseable {
+
+ ListenableFuture send(Message message);
+
+ ListenableFuture convertAndSend(Object message);
+
+ ListenableFuture convertAndSend(Object message, @Nullable MessagePostProcessor mpp);
+
+ ListenableFuture send(com.rabbitmq.stream.Message message);
+
+ MessageBuilder messageBuilder();
+
+ MessageConverter messageConverter();
+
+ StreamMessageConverter streamMessageConverter();
+
+ @Override
+ void close() throws AmqpException;
+
+}
+```
+
+The `RabbitStreamTemplate` implementation has the following constructor and properties:
+
+Example 2. RabbitStreamTemplate
+
+```
+public RabbitStreamTemplate(Environment environment, String streamName) {
+}
+
+public void setMessageConverter(MessageConverter messageConverter) {
+}
+
+public void setStreamConverter(StreamMessageConverter streamConverter) {
+}
+
+public synchronized void setProducerCustomizer(ProducerCustomizer producerCustomizer) {
+}
+```
+
+The `MessageConverter` is used in the `convertAndSend` methods to convert the object to a Spring AMQP `Message`.
+
+The `StreamMessageConverter` is used to convert from a Spring AMQP `Message` to a native stream `Message`.
+
+You can also send native stream `Message` s directly; with the `messageBuilder()` method provding access to the `Producer` 's message builder.
+
+The `ProducerCustomizer` provides a mechanism to customize the producer before it is built.
+
+Refer to the [Java Client Documentation](https://rabbitmq.github.io/rabbitmq-stream-java-client/stable/htmlsingle/) about customizing the `Environment` and `Producer`.
+
+#### 4.2.2. Receiving Messages
+
+Asynchronous message reception is provided by the `StreamListenerContainer` (and the `StreamRabbitListenerContainerFactory` when using `@RabbitListener`).
+
+The listener container requires an `Environment` as well as a single stream name.
+
+You can either receive Spring AMQP `Message` s using the classic `MessageListener`, or you can receive native stream `Message` s using a new interface:
+
+```
+public interface StreamMessageListener extends MessageListener {
+
+ void onStreamMessage(Message message, Context context);
+
+}
+```
+
+See [Message Listener Container Configuration](#containerAttributes) for information about supported properties.
+
+Similar the template, the container has a `ConsumerCustomizer` property.
+
+Refer to the [Java Client Documentation](https://rabbitmq.github.io/rabbitmq-stream-java-client/stable/htmlsingle/) about customizing the `Environment` and `Consumer`.
+
+When using `@RabbitListener`, configure a `StreamRabbitListenerContainerFactory`; at this time, most `@RabbitListener` properties (`concurrency`, etc) are ignored. Only `id`, `queues`, `autoStartup` and `containerFactory` are supported.
+In addition, `queues` can only contain one stream name.
+
+#### 4.2.3. Examples
+
+```
+@Bean
+RabbitStreamTemplate streamTemplate(Environment env) {
+ RabbitStreamTemplate template = new RabbitStreamTemplate(env, "test.stream.queue1");
+ template.setProducerCustomizer((name, builder) -> builder.name("test"));
+ return template;
+}
+
+@Bean
+RabbitListenerContainerFactory rabbitListenerContainerFactory(Environment env) {
+ return new StreamRabbitListenerContainerFactory(env);
+}
+
+@RabbitListener(queues = "test.stream.queue1")
+void listen(String in) {
+ ...
+}
+
+@Bean
+RabbitListenerContainerFactory nativeFactory(Environment env) {
+ StreamRabbitListenerContainerFactory factory = new StreamRabbitListenerContainerFactory(env);
+ factory.setNativeListener(true);
+ factory.setConsumerCustomizer((id, builder) -> {
+ builder.name("myConsumer")
+ .offset(OffsetSpecification.first())
+ .manualTrackingStrategy();
+ });
+ return factory;
+}
+
+@RabbitListener(id = "test", queues = "test.stream.queue2", containerFactory = "nativeFactory")
+void nativeMsg(Message in, Context context) {
+ ...
+ context.storeOffset();
+}
+```
+
+### 4.3. Logging Subsystem AMQP Appenders
+
+The framework provides logging appenders for some popular logging subsystems:
+
+* logback (since Spring AMQP version 1.4)
+
+* log4j2 (since Spring AMQP version 1.6)
+
+The appenders are configured by using the normal mechanisms for the logging subsystem, available properties are specified in the following sections.
+
+#### 4.3.1. Common properties
+
+The following properties are available with all appenders:
+
+| Property | Default | Description |
+|-------------------------------------------|-------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ```
+ ...
+
+
+
+```
+
+| |Starting with versions 1.6.10 and 1.7.3, by default, the log4j2 appender publishes the messages to RabbitMQ on the calling thread.
+
+ %n ]]>
+
+ foo:5672,bar:5672
+ 36
+ false
+ myApplication
+ %property{applicationId}.%c.%p
+ true
+ UTF-8
+ false
+ NON_PERSISTENT
+ true
+ false
+
+```
+
+Starting with version 1.7.1, the Logback `AmqpAppender` provides an `includeCallerData` option, which is `false` by default.
+Extracting caller data can be rather expensive, because the log event has to create a throwable and inspect it to determine the calling location.
+Therefore, by default, caller data associated with an event is not extracted when the event is added to the event queue.
+You can configure the appender to include caller data by setting the `includeCallerData` property to `true`.
+
+Starting with version 2.0.0, the Logback `AmqpAppender` supports [Logback encoders](https://logback.qos.ch/manual/encoders.html) with the `encoder` option.
+The `encoder` and `layout` options are mutually exclusive.
+
+#### 4.3.4. Customizing the Messages
+
+By default, AMQP appenders populate the following message properties:
+
+* `deliveryMode`
+
+* contentType
+
+* `contentEncoding`, if configured
+
+* `messageId`, if `generateId` is configured
+
+* `timestamp` of the log event
+
+* `appId`, if applicationId is configured
+
+In addition they populate headers with the following values:
+
+* `categoryName` of the log event
+
+* The level of the log event
+
+* `thread`: the name of the thread where log event happened
+
+* The location of the stack trace of the log event call
+
+* A copy of all the MDC properties (unless `addMdcAsHeaders` is set to `false`)
+
+Each of the appenders can be subclassed, letting you modify the messages before publishing.
+The following example shows how to customize log messages:
+
+```
+public class MyEnhancedAppender extends AmqpAppender {
+
+ @Override
+ public Message postProcessMessageBeforeSend(Message message, Event event) {
+ message.getMessageProperties().setHeader("foo", "bar");
+ return message;
+ }
+
+}
+```
+
+Starting with 2.2.4, the log4j2 `AmqpAppender` can be extended using `@PluginBuilderFactory` and extending also `AmqpAppender.Builder`
+
+```
+@Plugin(name = "MyEnhancedAppender", category = "Core", elementType = "appender", printObject = true)
+public class MyEnhancedAppender extends AmqpAppender {
+
+ public MyEnhancedAppender(String name, Filter filter, Layout layout,
+ boolean ignoreExceptions, AmqpManager manager, BlockingQueue eventQueue, String foo, String bar) {
+ super(name, filter, layout, ignoreExceptions, manager, eventQueue);
+
+ @Override
+ public Message postProcessMessageBeforeSend(Message message, Event event) {
+ message.getMessageProperties().setHeader("foo", "bar");
+ return message;
+ }
+
+ @PluginBuilderFactory
+ public static Builder newBuilder() {
+ return new Builder();
+ }
+
+ protected static class Builder extends AmqpAppender.Builder {
+
+ @Override
+ protected AmqpAppender buildInstance(String name, Filter filter, Layout layout,
+ boolean ignoreExceptions, AmqpManager manager, BlockingQueue eventQueue) {
+ return new MyEnhancedAppender(name, filter, layout, ignoreExceptions, manager, eventQueue);
+ }
+ }
+
+}
+```
+
+#### 4.3.5. Customizing the Client Properties
+
+You can add custom client properties by adding either string properties or more complex properties.
+
+##### Simple String Properties
+
+Each appender supports adding client properties to the RabbitMQ connection.
+
+The following example shows how to add a custom client property for logback:
+
+```
+
+ ...
+ thing1:thing2,cat:hat
+ ...
+
+```
+
+Example 3. log4j2
+
+```
+
+ ...
+
+
+```
+
+The properties are a comma-delimited list of `key:value` pairs.
+Keys and values cannot contain commas or colons.
+
+These properties appear on the RabbitMQ Admin UI when the connection is viewed.
+
+##### Advanced Technique for Logback
+
+You can subclass the Logback appender.
+Doing so lets you modify the client connection properties before the connection is established.
+The following example shows how to do so:
+
+```
+public class MyEnhancedAppender extends AmqpAppender {
+
+ private String thing1;
+
+ @Override
+ protected void updateConnectionClientProperties(Map clientProperties) {
+ clientProperties.put("thing1", this.thing1);
+ }
+
+ public void setThing1(String thing1) {
+ this.thing1 = thing1;
+ }
+
+}
+```
+
+Then you can add `thing2 ` to logback.xml.
+
+For String properties such as those shown in the preceding example, the previous technique can be used.
+Subclasses allow for adding richer properties (such as adding a `Map` or numeric property).
+
+#### 4.3.6. Providing a Custom Queue Implementation
+
+The `AmqpAppenders` use a `BlockingQueue` to asynchronously publish logging events to RabbitMQ.
+By default, a `LinkedBlockingQueue` is used.
+However, you can supply any kind of custom `BlockingQueue` implementation.
+
+The following example shows how to do so for Logback:
+
+```
+public class MyEnhancedAppender extends AmqpAppender {
+
+ @Override
+ protected BlockingQueue createEventQueue() {
+ return new ArrayBlockingQueue();
+ }
+
+}
+```
+
+The Log4j 2 appender supports using a [`BlockingQueueFactory`](https://logging.apache.org/log4j/2.x/manual/appenders.html#BlockingQueueFactory), as the following example shows:
+
+```
+
+ ...
+
+
+
+```
+
+### 4.4. Sample Applications
+
+The [Spring AMQP Samples](https://github.com/SpringSource/spring-amqp-samples) project includes two sample applications.
+The first is a simple “Hello World” example that demonstrates both synchronous and asynchronous message reception.
+It provides an excellent starting point for acquiring an understanding of the essential components.
+The second sample is based on a stock-trading use case to demonstrate the types of interaction that would be common in real world applications.
+In this chapter, we provide a quick walk-through of each sample so that you can focus on the most important components.
+The samples are both Maven-based, so you should be able to import them directly into any Maven-aware IDE (such as [SpringSource Tool Suite](https://www.springsource.org/sts)).
+
+#### 4.4.1. The “Hello World” Sample
+
+The “Hello World” sample demonstrates both synchronous and asynchronous message reception.
+You can import the `spring-rabbit-helloworld` sample into the IDE and then follow the discussion below.
+
+##### Synchronous Example
+
+Within the `src/main/java` directory, navigate to the `org.springframework.amqp.helloworld` package.
+Open the `HelloWorldConfiguration` class and notice that it contains the `@Configuration` annotation at the class level and notice some `@Bean` annotations at method-level.
+This is an example of Spring’s Java-based configuration.
+You can read more about that [here](https://docs.spring.io/spring/docs/current/spring-framework-reference/html/beans.html#beans-java).
+
+The following listing shows how the connection factory is created:
+
+```
+@Bean
+public CachingConnectionFactory connectionFactory() {
+ CachingConnectionFactory connectionFactory =
+ new CachingConnectionFactory("localhost");
+ connectionFactory.setUsername("guest");
+ connectionFactory.setPassword("guest");
+ return connectionFactory;
+}
+```
+
+The configuration also contains an instance of `RabbitAdmin`, which, by default, looks for any beans of type exchange, queue, or binding and then declares them on the broker.
+In fact, the `helloWorldQueue` bean that is generated in `HelloWorldConfiguration` is an example because it is an instance of `Queue`.
+
+The following listing shows the `helloWorldQueue` bean definition:
+
+```
+@Bean
+public Queue helloWorldQueue() {
+ return new Queue(this.helloWorldQueueName);
+}
+```
+
+Looking back at the `rabbitTemplate` bean configuration, you can see that it has the name of `helloWorldQueue` set as its `queue` property (for receiving messages) and for its `routingKey` property (for sending messages).
+
+Now that we have explored the configuration, we can look at the code that actually uses these components.
+First, open the `Producer` class from within the same package.
+It contains a `main()` method where the Spring `ApplicationContext` is created.
+
+The following listing shows the `main` method:
+
+```
+public static void main(String[] args) {
+ ApplicationContext context =
+ new AnnotationConfigApplicationContext(RabbitConfiguration.class);
+ AmqpTemplate amqpTemplate = context.getBean(AmqpTemplate.class);
+ amqpTemplate.convertAndSend("Hello World");
+ System.out.println("Sent: Hello World");
+}
+```
+
+In the preceding example, the `AmqpTemplate` bean is retrieved and used for sending a `Message`.
+Since the client code should rely on interfaces whenever possible, the type is `AmqpTemplate` rather than `RabbitTemplate`.
+Even though the bean created in `HelloWorldConfiguration` is an instance of `RabbitTemplate`, relying on the interface means that this code is more portable (you can change the configuration independently of the code).
+Since the `convertAndSend()` method is invoked, the template delegates to its `MessageConverter` instance.
+In this case, it uses the default `SimpleMessageConverter`, but a different implementation could be provided to the `rabbitTemplate` bean, as defined in `HelloWorldConfiguration`.
+
+Now open the `Consumer` class.
+It actually shares the same configuration base class, which means it shares the `rabbitTemplate` bean.
+That is why we configured that template with both a `routingKey` (for sending) and a `queue` (for receiving).
+As we describe in [`AmqpTemplate`](#amqp-template), you could instead pass the 'routingKey' argument to the send method and the 'queue' argument to the receive method.
+The `Consumer` code is basically a mirror image of the Producer, calling `receiveAndConvert()` rather than `convertAndSend()`.
+
+The following listing shows the main method for the `Consumer`:
+
+```
+public static void main(String[] args) {
+ ApplicationContext context =
+ new AnnotationConfigApplicationContext(RabbitConfiguration.class);
+ AmqpTemplate amqpTemplate = context.getBean(AmqpTemplate.class);
+ System.out.println("Received: " + amqpTemplate.receiveAndConvert());
+}
+```
+
+If you run the `Producer` and then run the `Consumer`, you should see `Received: Hello World` in the console output.
+
+##### Asynchronous Example
+
+[Synchronous Example](#hello-world-sync) walked through the synchronous Hello World sample.
+This section describes a slightly more advanced but significantly more powerful option.
+With a few modifications, the Hello World sample can provide an example of asynchronous reception, also known as message-driven POJOs.
+In fact, there is a sub-package that provides exactly that: `org.springframework.amqp.samples.helloworld.async`.
+
+Again, we start with the sending side.
+Open the `ProducerConfiguration` class and notice that it creates a `connectionFactory` and a `rabbitTemplate` bean.
+This time, since the configuration is dedicated to the message sending side, we do not even need any queue definitions, and the `RabbitTemplate` has only the 'routingKey' property set.
+Recall that messages are sent to an exchange rather than being sent directly to a queue.
+The AMQP default exchange is a direct exchange with no name.
+All queues are bound to that default exchange with their name as the routing key.
+That is why we only need to provide the routing key here.
+
+The following listing shows the `rabbitTemplate` definition:
+
+```
+public RabbitTemplate rabbitTemplate() {
+ RabbitTemplate template = new RabbitTemplate(connectionFactory());
+ template.setRoutingKey(this.helloWorldQueueName);
+ return template;
+}
+```
+
+Since this sample demonstrates asynchronous message reception, the producing side is designed to continuously send messages (if it were a message-per-execution model like the synchronous version, it would not be quite so obvious that it is, in fact, a message-driven consumer).
+The component responsible for continuously sending messages is defined as an inner class within the `ProducerConfiguration`.
+It is configured to run every three seconds.
+
+The following listing shows the component:
+
+```
+static class ScheduledProducer {
+
+ @Autowired
+ private volatile RabbitTemplate rabbitTemplate;
+
+ private final AtomicInteger counter = new AtomicInteger();
+
+ @Scheduled(fixedRate = 3000)
+ public void sendMessage() {
+ rabbitTemplate.convertAndSend("Hello World " + counter.incrementAndGet());
+ }
+}
+```
+
+You do not need to understand all of the details, since the real focus should be on the receiving side (which we cover next).
+However, if you are not yet familiar with Spring task scheduling support, you can learn more [here](https://docs.spring.io/spring/docs/current/spring-framework-reference/html/scheduling.html#scheduling-annotation-support).
+The short story is that the `postProcessor` bean in the `ProducerConfiguration` registers the task with a scheduler.
+
+Now we can turn to the receiving side.
+To emphasize the message-driven POJO behavior, we start with the component that react to the messages.
+The class is called `HelloWorldHandler` and is shown in the following listing:
+
+```
+public class HelloWorldHandler {
+
+ public void handleMessage(String text) {
+ System.out.println("Received: " + text);
+ }
+
+}
+```
+
+That class is a POJO.
+It does not extend any base class, it does not implement any interfaces, and it does not even contain any imports.
+It is being “adapted” to the `MessageListener` interface by the Spring AMQP `MessageListenerAdapter`.
+You can then configure that adapter on a `SimpleMessageListenerContainer`.
+For this sample, the container is created in the `ConsumerConfiguration` class.
+You can see the POJO wrapped in the adapter there.
+
+The following listing shows how the `listenerContainer` is defined:
+
+```
+@Bean
+public SimpleMessageListenerContainer listenerContainer() {
+ SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
+ container.setConnectionFactory(connectionFactory());
+ container.setQueueName(this.helloWorldQueueName);
+ container.setMessageListener(new MessageListenerAdapter(new HelloWorldHandler()));
+ return container;
+}
+```
+
+The `SimpleMessageListenerContainer` is a Spring lifecycle component and, by default, starts automatically.
+If you look in the `Consumer` class, you can see that its `main()` method consists of nothing more than a one-line bootstrap to create the `ApplicationContext`.
+The Producer’s `main()` method is also a one-line bootstrap, since the component whose method is annotated with `@Scheduled` also starts automatically.
+You can start the `Producer` and `Consumer` in any order, and you should see messages being sent and received every three seconds.
+
+#### 4.4.2. Stock Trading
+
+The Stock Trading sample demonstrates more advanced messaging scenarios than [the Hello World sample](#hello-world-sample).
+However, the configuration is very similar, if a bit more involved.
+Since we walked through the Hello World configuration in detail, here, we focus on what makes this sample different.
+There is a server that pushes market data (stock quotations) to a topic exchange.
+Then, clients can subscribe to the market data feed by binding a queue with a routing pattern (for example,`app.stock.quotes.nasdaq.*`).
+The other main feature of this demo is a request-reply “stock trade” interaction that is initiated by the client and handled by the server.
+That involves a private `replyTo` queue that is sent by the client within the order request message itself.
+
+The server’s core configuration is in the `RabbitServerConfiguration` class within the `org.springframework.amqp.rabbit.stocks.config.server` package.
+It extends the `AbstractStockAppRabbitConfiguration`.
+That is where the resources common to the server and client are defined, including the market data topic exchange (whose name is 'app.stock.marketdata') and the queue that the server exposes for stock trades (whose name is 'app.stock.request').
+In that common configuration file, you also see that a `Jackson2JsonMessageConverter` is configured on the `RabbitTemplate`.
+
+The server-specific configuration consists of two things.
+First, it configures the market data exchange on the `RabbitTemplate` so that it does not need to provide that exchange name with every call to send a `Message`.
+It does this within an abstract callback method defined in the base configuration class.
+The following listing shows that method:
+
+```
+public void configureRabbitTemplate(RabbitTemplate rabbitTemplate) {
+ rabbitTemplate.setExchange(MARKET_DATA_EXCHANGE_NAME);
+}
+```
+
+Second, the stock request queue is declared.
+It does not require any explicit bindings in this case, because it is bound to the default no-name exchange with its own name as the routing key.
+As mentioned earlier, the AMQP specification defines that behavior.
+The following listing shows the definition of the `stockRequestQueue` bean:
+
+```
+@Bean
+public Queue stockRequestQueue() {
+ return new Queue(STOCK_REQUEST_QUEUE_NAME);
+}
+```
+
+Now that you have seen the configuration of the server’s AMQP resources, navigate to the `org.springframework.amqp.rabbit.stocks` package under the `src/test/java` directory.
+There, you can see the actual `Server` class that provides a `main()` method.
+It creates an `ApplicationContext` based on the `server-bootstrap.xml` config file.
+There, you can see the scheduled task that publishes dummy market data.
+That configuration relies upon Spring’s `task` namespace support.
+The bootstrap config file also imports a few other files.
+The most interesting one is `server-messaging.xml`, which is directly under `src/main/resources`.
+There, you can see the `messageListenerContainer` bean that is responsible for handling the stock trade requests.
+Finally, have a look at the `serverHandler` bean that is defined in `server-handlers.xml` (which is also in 'src/main/resources').
+That bean is an instance of the `ServerHandler` class and is a good example of a message-driven POJO that can also send reply messages.
+Notice that it is not itself coupled to the framework or any of the AMQP concepts.
+It accepts a `TradeRequest` and returns a `TradeResponse`.
+The following listing shows the definition of the `handleMessage` method:
+
+```
+public TradeResponse handleMessage(TradeRequest tradeRequest) { ...
+}
+```
+
+Now that we have seen the most important configuration and code for the server, we can turn to the client.
+The best starting point is probably `RabbitClientConfiguration`, in the `org.springframework.amqp.rabbit.stocks.config.client` package.
+Notice that it declares two queues without providing explicit names.
+The following listing shows the bean definitions for the two queues:
+
+```
+@Bean
+public Queue marketDataQueue() {
+ return amqpAdmin().declareQueue();
+}
+
+@Bean
+public Queue traderJoeQueue() {
+ return amqpAdmin().declareQueue();
+}
+```
+
+Those are private queues, and unique names are generated automatically.
+The first generated queue is used by the client to bind to the market data exchange that has been exposed by the server.
+Recall that, in AMQP, consumers interact with queues while producers interact with exchanges.
+The “binding” of queues to exchanges is what tells the broker to deliver (or route) messages from a given exchange to a queue.
+Since the market data exchange is a topic exchange, the binding can be expressed with a routing pattern.
+The `RabbitClientConfiguration` does so with a `Binding` object, and that object is generated with the `BindingBuilder` fluent API.
+The following listing shows the `Binding`:
+
+```
+@Value("${stocks.quote.pattern}")
+private String marketDataRoutingKey;
+
+@Bean
+public Binding marketDataBinding() {
+ return BindingBuilder.bind(
+ marketDataQueue()).to(marketDataExchange()).with(marketDataRoutingKey);
+}
+```
+
+Notice that the actual value has been externalized in a properties file (`client.properties` under `src/main/resources`), and that we use Spring’s `@Value` annotation to inject that value.
+This is generally a good idea.
+Otherwise, the value would have been hardcoded in a class and unmodifiable without recompilation.
+In this case, it is much easier to run multiple versions of the client while making changes to the routing pattern used for binding.
+We can try that now.
+
+Start by running `org.springframework.amqp.rabbit.stocks.Server` and then `org.springframework.amqp.rabbit.stocks.Client`.
+You should see dummy quotations for `NASDAQ` stocks, because the current value associated with the 'stocks.quote.pattern' key in client.properties is 'app.stock.quotes.nasdaq.**'.
+Now, while keeping the existing `Server` and `Client` running, change that property value to 'app.stock.quotes.nyse.**' and start a second `Client` instance.
+You should see that the first client still receives NASDAQ quotes while the second client receives NYSE quotes.
+You could instead change the pattern to get all stocks or even an individual ticker.
+
+The final feature we explore is the request-reply interaction from the client’s perspective.
+Recall that we have already seen the `ServerHandler` that accepts `TradeRequest` objects and returns `TradeResponse` objects.
+The corresponding code on the `Client` side is `RabbitStockServiceGateway` in the `org.springframework.amqp.rabbit.stocks.gateway` package.
+It delegates to the `RabbitTemplate` in order to send messages.
+The following listing shows the `send` method:
+
+```
+public void send(TradeRequest tradeRequest) {
+ getRabbitTemplate().convertAndSend(tradeRequest, new MessagePostProcessor() {
+ public Message postProcessMessage(Message message) throws AmqpException {
+ message.getMessageProperties().setReplyTo(new Address(defaultReplyToQueue));
+ try {
+ message.getMessageProperties().setCorrelationId(
+ UUID.randomUUID().toString().getBytes("UTF-8"));
+ }
+ catch (UnsupportedEncodingException e) {
+ throw new AmqpException(e);
+ }
+ return message;
+ }
+ });
+}
+```
+
+Notice that, prior to sending the message, it sets the `replyTo` address.
+It provides the queue that was generated by the `traderJoeQueue` bean definition (shown earlier).
+The following listing shows the `@Bean` definition for the `StockServiceGateway` class itself:
+
+```
+@Bean
+public StockServiceGateway stockServiceGateway() {
+ RabbitStockServiceGateway gateway = new RabbitStockServiceGateway();
+ gateway.setRabbitTemplate(rabbitTemplate());
+ gateway.setDefaultReplyToQueue(traderJoeQueue());
+ return gateway;
+}
+```
+
+If you are no longer running the server and client, start them now.
+Try sending a request with the format of '100 TCKR'.
+After a brief artificial delay that simulates “processing” of the request, you should see a confirmation message appear on the client.
+
+#### 4.4.3. Receiving JSON from Non-Spring Applications
+
+Spring applications, when sending JSON, set the `*TypeId*` header to the fully qualified class name to assist the receiving application in converting the JSON back to a Java object.
+
+The `spring-rabbit-json` sample explores several techniques to convert the JSON from a non-Spring application.
+
+See also [Jackson2JsonMessageConverter](#json-message-converter) as well as the [Javadoc for the `DefaultClassMapper`](https://docs.spring.io/spring-amqp/docs/current/api/index.html?org/springframework/amqp/support/converter/DefaultClassMapper.html).
+
+### 4.5. Testing Support
+
+Writing integration for asynchronous applications is necessarily more complex than testing simpler applications.
+This is made more complex when abstractions such as the `@RabbitListener` annotations come into the picture.
+The question is how to verify that, after sending a message, the listener received the message as expected.
+
+The framework itself has many unit and integration tests.
+Some using mocks while, others use integration testing with a live RabbitMQ broker.
+You can consult those tests for some ideas for testing scenarios.
+
+Spring AMQP version 1.6 introduced the `spring-rabbit-test` jar, which provides support for testing some of these more complex scenarios.
+It is anticipated that this project will expand over time, but we need community feedback to make suggestions for the features needed to help with testing.
+Please use [JIRA](https://jira.spring.io/browse/AMQP) or [GitHub Issues](https://github.com/spring-projects/spring-amqp/issues) to provide such feedback.
+
+#### 4.5.1. @SpringRabbitTest
+
+Use this annotation to add infrastructure beans to the Spring test `ApplicationContext`.
+This is not necessary when using, for example `@SpringBootTest` since Spring Boot’s auto configuration will add the beans.
+
+Beans that are registered are:
+
+* `CachingConnectionFactory` (`autoConnectionFactory`). If `@RabbitEnabled` is present, its connectionn factory is used.
+
+* `RabbitTemplate` (`autoRabbitTemplate`)
+
+* `RabbitAdmin` (`autoRabbitAdmin`)
+
+* `RabbitListenerContainerFactory` (`autoContainerFactory`)
+
+In addition, the beans associated with `@EnableRabbit` (to support `@RabbitListener`) are added.
+
+Example 4. Junit5 example
+
+```
+@SpringJunitConfig
+@SpringRabbitTest
+public class MyRabbitTests {
+
+ @Autowired
+ private RabbitTemplate template;
+
+ @Autowired
+ private RabbitAdmin admin;
+
+ @Autowired
+ private RabbitListenerEndpointRegistry registry;
+
+ @Test
+ void test() {
+ ...
+ }
+
+ @Configuration
+ public static class Config {
+
+ ...
+
+ }
+
+}
+```
+
+With JUnit4, replace `@SpringJunitConfig` with `@RunWith(SpringRunnner.class)`.
+
+#### 4.5.2. Mockito `Answer` Implementations
+
+There are currently two `Answer` implementations to help with testing.
+
+The first, `LatchCountDownAndCallRealMethodAnswer`, provides an `Answer` that returns `null` and counts down a latch.
+The following example shows how to use `LatchCountDownAndCallRealMethodAnswer`:
+
+```
+LatchCountDownAndCallRealMethodAnswer answer = this.harness.getLatchAnswerFor("myListener", 2);
+doAnswer(answer)
+ .when(listener).foo(anyString(), anyString());
+
+...
+
+assertThat(answer.await(10)).isTrue();
+```
+
+The second, `LambdaAnswer` provides a mechanism to optionally call the real method and provides an opportunity
+to return a custom result, based on the `InvocationOnMock` and the result (if any).
+
+Consider the following POJO:
+
+```
+public class Thing {
+
+ public String thing(String thing) {
+ return thing.toUpperCase();
+ }
+
+}
+```
+
+The following class tests the `Thing` POJO:
+
+```
+Thing thing = spy(new Thing());
+
+doAnswer(new LambdaAnswer(true, (i, r) -> r + r))
+ .when(thing).thing(anyString());
+assertEquals("THINGTHING", thing.thing("thing"));
+
+doAnswer(new LambdaAnswer(true, (i, r) -> r + i.getArguments()[0]))
+ .when(thing).thing(anyString());
+assertEquals("THINGthing", thing.thing("thing"));
+
+doAnswer(new LambdaAnswer(false, (i, r) ->
+ "" + i.getArguments()[0] + i.getArguments()[0])).when(thing).thing(anyString());
+assertEquals("thingthing", thing.thing("thing"));
+```
+
+Starting with version 2.2.3, the answers capture any exceptions thrown by the method under test.
+Use `answer.getExceptions()` to get a reference to them.
+
+When used in conjunction with the [`@RabbitListenerTest` and `RabbitListenerTestHarness`](#test-harness) use `harness.getLambdaAnswerFor("listenerId", true, …)` to get a properly constructed answer for the listener.
+
+#### 4.5.3. `@RabbitListenerTest` and `RabbitListenerTestHarness`
+
+Annotating one of your `@Configuration` classes with `@RabbitListenerTest` causes the framework to replace the
+standard `RabbitListenerAnnotationBeanPostProcessor` with a subclass called `RabbitListenerTestHarness` (it also enables`@RabbitListener` detection through `@EnableRabbit`).
+
+The `RabbitListenerTestHarness` enhances the listener in two ways.
+First, it wraps the listener in a `Mockito Spy`, enabling normal `Mockito` stubbing and verification operations.
+It can also add an `Advice` to the listener, enabling access to the arguments, result, and any exceptions that are thrown.
+You can control which (or both) of these are enabled with attributes on the `@RabbitListenerTest`.
+The latter is provided for access to lower-level data about the invocation.
+It also supports blocking the test thread until the async listener is called.
+
+| |`final` `@RabbitListener` methods cannot be spied or advised.`.
+The following example shows how to configure an inbound channel adapter:
+
+```
+`.
+You can optionally provide a 'routing-key' in addition to the exchange name.
+The following example shows how to define an outbound channel adapter:
+
+```
+`.
+The following example shows how to define an inbound gateway:
+
+```
+`.
+You can optionally provide a 'routing-key' in addition to the exchange name.
+The following example shows how to define an outbound gateway:
+
+```
+>` (and others) and should use `Declarables` beans instead.
+By default, the old mechanism is disabled.
+See [Declaring Collections of Exchanges, Queues, and Bindings](#collection-declaration) for more information.
+
+`AnonymousQueue` instances are now declared with `x-queue-master-locator` set to `client-local` by default, to ensure the queues are created on the node the application is connected to.
+See [Configuring the Broker](#broker-configuration) for more information.
+
+##### RabbitTemplate Changes
+
+You can now configure the `RabbitTemplate` with the `noLocalReplyConsumer` option to control a `noLocal` flag for reply consumers in the `sendAndReceive()` operations.
+See [Request/Reply Messaging](#request-reply) for more information.
+
+`CorrelationData` for publisher confirmations now has a `ListenableFuture`, which you can use to get the acknowledgment instead of using a callback.
+When returns and confirmations are enabled, the correlation data, if provided, is populated with the returned message.
+See [Correlated Publisher Confirms and Returns](#template-confirms) for more information.
+
+A method called `replyTimedOut` is now provided to notify subclasses that a reply has timed out, allowing for any state cleanup.
+See [Reply Timeout](#reply-timeout) for more information.
+
+You can now specify an `ErrorHandler` to be invoked when using request/reply with a `DirectReplyToMessageListenerContainer` (the default) when exceptions occur when replies are delivered (for example, late replies).
+See `setReplyErrorHandler` on the `RabbitTemplate`.
+(Also since 2.0.11).
+
+##### Message Conversion
+
+We introduced a new `Jackson2XmlMessageConverter` to support converting messages from and to XML format.
+See [`Jackson2XmlMessageConverter`](#jackson2xml) for more information.
+
+##### Management REST API
+
+The `RabbitManagementTemplate` is now deprecated in favor of the direct `com.rabbitmq.http.client.Client` (or `com.rabbitmq.http.client.ReactorNettyClient`) usage.
+See [RabbitMQ REST API](#management-rest-api) for more information.
+
+##### `@RabbitListener` Changes
+
+The listener container factory can now be configured with a `RetryTemplate` and, optionally, a `RecoveryCallback` used when sending replies.
+See [Enable Listener Endpoint Annotations](#async-annotation-driven-enable) for more information.
+
+##### Async `@RabbitListener` Return
+
+`@RabbitListener` methods can now return `ListenableFuture` or `Mono`.
+See [Asynchronous `@RabbitListener` Return Types](#async-returns) for more information.
+
+##### Connection Factory Bean Changes
+
+By default, the `RabbitConnectionFactoryBean` now calls `enableHostnameVerification()`.
+To revert to the previous behavior, set the `enableHostnameVerification` property to `false`.
+
+##### Connection Factory Changes
+
+The `CachingConnectionFactory` now unconditionally disables auto-recovery in the underlying RabbitMQ `ConnectionFactory`, even if a pre-configured instance is provided in a constructor.
+While steps have been taken to make Spring AMQP compatible with auto recovery, certain corner cases have arisen where issues remain.
+Spring AMQP has had its own recovery mechanism since 1.0.0 and does not need to use the recovery provided by the client.
+While it is still possible to enable the feature (using `cachingConnectionFactory.getRabbitConnectionFactory()` `.setAutomaticRecoveryEnabled()`) after the `CachingConnectionFactory` is constructed, **we strongly recommend that you not do so**.
+We recommend that you use a separate RabbitMQ `ConnectionFactory` if you need auto recovery connections when using the client factory directly (rather than using Spring AMQP components).
+
+##### Listener Container Changes
+
+The default `ConditionalRejectingErrorHandler` now completely discards messages that cause fatal errors if an `x-death` header is present.
+See [Exception Handling](#exception-handling) for more information.
+
+##### Immediate requeue
+
+A new `ImmediateRequeueAmqpException` is introduced to notify a listener container that the message has to be re-queued.
+To use this feature, a new `ImmediateRequeueMessageRecoverer` implementation is added.
+
+See [Message Listeners and the Asynchronous Case](#async-listeners) for more information.
+
+#### A.2.4. Changes in 2.0 Since 1.7
+
+##### Using `CachingConnectionFactory`
+
+Starting with version 2.0.2, you can configure the `RabbitTemplate` to use a different connection to that used by listener containers.
+This change avoids deadlocked consumers when producers are blocked for any reason.
+See [Using a Separate Connection](#separate-connection) for more information.
+
+##### AMQP Client library
+
+Spring AMQP now uses the new 5.0.x version of the `amqp-client` library provided by the RabbitMQ team.
+This client has auto recovery configured by default.
+See [RabbitMQ Automatic Connection/Topology recovery](#auto-recovery).
+
+| |As of version 4.0, the client enables automatic recovery by default.` argument, letting the caller specify the type to which to convert the result.
+This is particularly useful for complex types or when type information is not conveyed in message headers.
+It requires a `SmartMessageConverter` such as the `Jackson2JsonMessageConverter`.
+See [Receiving Messages](#receiving-messages), [Request/Reply Messaging](#request-reply), [Async Rabbit Template](#async-template), and [Converting From a `Message` With `RabbitTemplate`](#json-complex) for more information.
+
+You can now use a `RabbitTemplate` to perform multiple operations on a dedicated channel.
+See [Scoped Operations](#scoped-operations) for more information.
+
+##### Listener Adapter
+
+A convenient `FunctionalInterface` is available for using lambdas with the `MessageListenerAdapter`.
+See [`MessageListenerAdapter`](#message-listener-adapter) for more information.
+
+##### Listener Container Changes
+
+###### Prefetch Default Value
+
+The prefetch default value used to be 1, which could lead to under-utilization of efficient consumers.
+The default prefetch value is now 250, which should keep consumers busy in most common scenarios and,
+thus, improve throughput.
+
+| |There are scenarios where the prefetch value should` component as an alternative `reply-queue`.
+See [Request/Reply Messaging](#request-reply) for more information.
+(Also available in 1.4.4 as a setter on the `RabbitTemplate`).
+
+###### Blocking `receive` Methods
+
+The `RabbitTemplate` now supports blocking in `receive` and `convertAndReceive` methods.
+See [Polling Consumer](#polling-consumer) for more information.
+
+###### Mandatory with `sendAndReceive` Methods
+
+When the `mandatory` flag is set when using the `sendAndReceive` and `convertSendAndReceive` methods, the calling thread
+throws an `AmqpMessageReturnedException` if the request message cannot be deliverted.
+See [Reply Timeout](#reply-timeout) for more information.
+
+###### Improper Reply Listener Configuration
+
+The framework tries to verify proper configuration of a reply listener container when using a named reply queue.
+
+See [Reply Listener Container](#reply-listener) for more information.
+
+##### `RabbitManagementTemplate` Added
+
+The `RabbitManagementTemplate` has been introduced to monitor and configure the RabbitMQ Broker by using the REST API provided by its [management plugin](https://www.rabbitmq.com/management.html).
+See [RabbitMQ REST API](#management-rest-api) for more information.
+
+#####
+
+| |The `id` attribute on the ``.
+You can iterate over this group to start and stop containers.
+
+##### Class-Level `@RabbitListener`
+
+The `@RabbitListener` annotation can now be applied at the class level.
+Together with the new `@RabbitHandler` method annotation, this lets you select the handler method based on payload type.
+See [Multi-method Listeners](#annotation-method-selection) for more information.
+
+##### `SimpleMessageListenerContainer`: BackOff Support
+
+The `SimpleMessageListenerContainer` can now be supplied with a `BackOff` instance for `consumer` startup recovery.
+See [Message Listener Container Configuration](#containerAttributes) for more information.
+
+##### Channel Close Logging
+
+A mechanism to control the log levels of channel closure has been introduced.
+See [Logging Channel Close Events](#channel-close-logging).
+
+##### Application Events
+
+The `SimpleMessageListenerContainer` now emits application events when consumers fail.
+See [Consumer Events](#consumer-events) for more information.
+
+##### Consumer Tag Configuration
+
+Previously, the consumer tags for asynchronous consumers were generated by the broker.
+With this release, it is now possible to supply a naming strategy to the listener container.
+See [Consumer Tags](#consumerTags).
+
+##### Using `MessageListenerAdapter`
+
+The `MessageListenerAdapter` now supports a map of queue names (or consumer tags) to method names, to determine
+which delegate method to call based on the queue from which the message was received.
+
+##### `LocalizedQueueConnectionFactory` Added
+
+`LocalizedQueueConnectionFactory` is a new connection factory that connects to the node in a cluster where a mirrored queue actually resides.
+
+See [Queue Affinity and the `LocalizedQueueConnectionFactory`](#queue-affinity).
+
+##### Anonymous Queue Naming
+
+Starting with version 1.5.3, you can now control how `AnonymousQueue` names are generated.
+See [`AnonymousQueue`](#anonymous-queue) for more information.
+
+#### A.2.9. Changes in 1.4 Since 1.3
+
+##### `@RabbitListener` Annotation
+
+POJO listeners can be annotated with `@RabbitListener`, enabled by `@EnableRabbit` or `` to prevent these re-declarations.
+See [`auto-delete` Queues](#lc-auto-delete).
+
+##### `RabbitTemplate`: `mandatory` and `connectionFactorySelector` Expressions
+
+The `mandatoryExpression`, `sendConnectionFactorySelectorExpression`, and `receiveConnectionFactorySelectorExpression` SpEL Expression`s properties have been added to `RabbitTemplate`.
+The `mandatoryExpression` is used to evaluate a `mandatory` boolean value against each request message when a `ReturnCallback` is in use.
+See [Correlated Publisher Confirms and Returns](#template-confirms).
+The `sendConnectionFactorySelectorExpression` and `receiveConnectionFactorySelectorExpression` are used when an `AbstractRoutingConnectionFactory` is provided, to determine the `lookupKey` for the target `ConnectionFactory` at runtime on each AMQP protocol interaction operation.
+See [Routing Connection Factory](#routing-connection-factory).
+
+##### Listeners and the Routing Connection Factory
+
+You can configure a `SimpleMessageListenerContainer` with a routing connection factory to enable connection selection based on the queue names.
+See [Routing Connection Factory](#routing-connection-factory).
+
+##### `RabbitTemplate`: `RecoveryCallback` Option
+
+The `recoveryCallback` property has been added for use in the `retryTemplate.execute()`.
+See [Adding Retry Capabilities](#template-retry).
+
+##### `MessageConversionException` Change
+
+This exception is now a subclass of `AmqpException`.
+Consider the following code:
+
+```
+try {
+ template.convertAndSend("thing1", "thing2", "cat");
+}
+catch (AmqpException e) {
+ ...
+}
+catch (MessageConversionException e) {
+ ...
+}
+```
+
+The second catch block is no longer reachable and needs to be moved above the catch-all `AmqpException` catch block.
+
+##### RabbitMQ 3.4 Compatibility
+
+Spring AMQP is now compatible with the RabbitMQ 3.4, including direct reply-to.
+See [Compatibility](#compatibility) and [RabbitMQ Direct reply-to](#direct-reply-to) for more information.
+
+##### `ContentTypeDelegatingMessageConverter` Added
+
+The `ContentTypeDelegatingMessageConverter` has been introduced to select the `MessageConverter` to use, based on the `contentType` property in the `MessageProperties`.
+See [Message Converters](#message-converters) for more information.
+
+#### A.2.10. Changes in 1.3 Since 1.2
+
+##### Listener Concurrency
+
+The listener container now supports dynamic scaling of the number of consumers based on workload, or you can programmatically change the concurrency without stopping the container.
+See [Listener Concurrency](#listener-concurrency).
+
+##### Listener Queues
+
+The listener container now permits the queues on which it listens to be modified at runtime.
+Also, the container now starts if at least one of its configured queues is available for use.
+See [Listener Container Queues](#listener-queues)
+
+This listener container now redeclares any auto-delete queues during startup.
+See [`auto-delete` Queues](#lc-auto-delete).
+
+##### Consumer Priority
+
+The listener container now supports consumer arguments, letting the `x-priority` argument be set.
+See [Consumer Priority](#consumer-priority).
+
+##### Exclusive Consumer
+
+You can now configure `SimpleMessageListenerContainer` with a single `exclusive` consumer, preventing other consumers from listening to the queue.
+See [Exclusive Consumer](#exclusive-consumer).
+
+##### Rabbit Admin
+
+You can now have the broker generate the queue name, regardless of `durable`, `autoDelete`, and `exclusive` settings.
+See [Configuring the Broker](#broker-configuration).
+
+##### Direct Exchange Binding
+
+Previously, omitting the `key` attribute from a `binding` element of a `direct-exchange` configuration caused the queue or exchange to be bound with an empty string as the routing key.
+Now it is bound with the the name of the provided `Queue` or `Exchange`.
+If you wish to bind with an empty string routing key, you need to specify `key=""`.
+
+##### `AmqpTemplate` Changes
+
+The `AmqpTemplate` now provides several synchronous `receiveAndReply` methods.
+These are implemented by the `RabbitTemplate`.
+For more information see [Receiving Messages](#receiving-messages).
+
+The `RabbitTemplate` now supports configuring a `RetryTemplate` to attempt retries (with optional back-off policy) for when the broker is not available.
+For more information see [Adding Retry Capabilities](#template-retry).
+
+##### Caching Connection Factory
+
+You can now configure the caching connection factory to cache `Connection` instances and their `Channel` instances instead of using a single connection and caching only `Channel` instances.
+See [Connection and Resource Management](#connections).
+
+##### Binding Arguments
+
+The `` of the `` now supports parsing of the `` sub-element.
+You can now configure the `` of the `` with a `key/value` attribute pair (to match on a single header) or with a `` sub-element (allowing matching on multiple headers).
+These options are mutually exclusive.
+See [Headers Exchange](#headers-exchange).
+
+##### Routing Connection Factory
+
+A new `SimpleRoutingConnectionFactory` has been introduced.
+It allows configuration of `ConnectionFactories` mapping, to determine the target `ConnectionFactory` to use at runtime.
+See [Routing Connection Factory](#routing-connection-factory).
+
+##### `MessageBuilder` and `MessagePropertiesBuilder`
+
+“Fluent APIs” for building messages or message properties are now provided.
+See [Message Builder API](#message-builder).
+
+##### `RetryInterceptorBuilder` Change
+
+A “Fluent API” for building listener container retry interceptors is now provided.
+See [Failures in Synchronous Operations and Options for Retry](#retry).
+
+##### `RepublishMessageRecoverer` Added
+
+This new `MessageRecoverer` is provided to allow publishing a failed message to another queue (including stack trace information in the header) when retries are exhausted.
+See [Message Listeners and the Asynchronous Case](#async-listeners).
+
+#####
+
+A default `ConditionalRejectingErrorHandler` has been added to the listener container.
+This error handler detects fatal message conversion problems and instructs the container to reject the message to prevent the broker from continually redelivering the unconvertible message.
+See [Exception Handling](#exception-handling).
+
+#####
+
+The `SimpleMessageListenerContainer` now has a property called `missingQueuesFatal` (default: `true`).
+Previously, missing queues were always fatal.
+See [Message Listener Container Configuration](#containerAttributes).
+
+#### A.2.11. Changes to 1.2 Since 1.1
+
+##### RabbitMQ Version
+
+Spring AMQP now uses RabbitMQ 3.1.x by default (but retains compatibility with earlier versions).
+Certain deprecations have been added for features no longer supported by RabbitMQ 3.1.x — federated exchanges and the `immediate` property on the `RabbitTemplate`.
+
+##### Rabbit Admin
+
+`RabbitAdmin` now provides an option to let exchange, queue, and binding declarations continue when a declaration fails.
+Previously, all declarations stopped on a failure.
+By setting `ignore-declaration-exceptions`, such exceptions are logged (at the `WARN` level), but further declarations continue.
+An example where this might be useful is when a queue declaration fails because of a slightly different `ttl` setting that would normally stop other declarations from proceeding.
+
+`RabbitAdmin` now provides an additional method called `getQueueProperties()`.
+You can use this determine if a queue exists on the broker (returns `null` for a non-existent queue).
+In addition, it returns the current number of messages in the queue as well as the current number of consumers.
+
+##### Rabbit Template
+
+Previously, when the `…sendAndReceive()` methods were used with a fixed reply queue, two custom headers were used for correlation data and to retain and restore reply queue information.
+With this release, the standard message property (`correlationId`) is used by default, although you can specify a custom property to use instead.
+In addition, nested `replyTo` information is now retained internally in the template, instead of using a custom header.
+
+The `immediate` property is deprecated.
+You must not set this property when using RabbitMQ 3.0.x or greater.
+
+##### JSON Message Converters
+
+A Jackson 2.x `MessageConverter` is now provided, along with the existing converter that uses Jackson 1.x.
+
+##### Automatic Declaration of Queues and Other Items
+
+Previously, when declaring queues, exchanges and bindings, you could not define which connection factory was used for the declarations.
+Each `RabbitAdmin` declared all components by using its connection.
+
+Starting with this release, you can now limit declarations to specific `RabbitAdmin` instances.
+See [Conditional Declaration](#conditional-declaration).
+
+##### AMQP Remoting
+
+Facilities are now provided for using Spring remoting techniques, using AMQP as the transport for the RPC calls.
+For more information see [Spring Remoting with AMQP](#remoting)
+
+##### Requested Heart Beats
+
+Several users have asked for the underlying client connection factory’s `requestedHeartBeats` property to be exposed on the Spring AMQP `CachingConnectionFactory`.
+This is now available.
+Previously, it was necessary to configure the AMQP client factory as a separate bean and provide a reference to it in the `CachingConnectionFactory`.
+
+#### A.2.12. Changes to 1.1 Since 1.0
+
+##### General
+
+Spring-AMQP is now built with Gradle.
+
+Adds support for publisher confirms and returns.
+
+Adds support for HA queues and broker failover.
+
+Adds support for dead letter exchanges and dead letter queues.
+
+##### AMQP Log4j Appender
+
+Adds an option to support adding a message ID to logged messages.
+
+Adds an option to allow the specification of a `Charset` name to be used when converting `String` to `byte[]`.
\ No newline at end of file
diff --git a/docs/en/spring-for-graphql/READEME.md b/docs/en/spring-batch/README.md
similarity index 100%
rename from docs/en/spring-for-graphql/READEME.md
rename to docs/en/spring-batch/README.md
diff --git a/docs/en/spring-batch/appendix.md b/docs/en/spring-batch/appendix.md
new file mode 100644
index 0000000000000000000000000000000000000000..10e84b5cc95996eff85bcf539d44c70e52435319
--- /dev/null
+++ b/docs/en/spring-batch/appendix.md
@@ -0,0 +1,48 @@
+## Appendix A: List of ItemReaders and ItemWriters
+
+### Item Readers
+
+| Item Reader | Description |
+|----------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+|AbstractItemCountingItemStreamItemReader| Abstract base class that provides basic
+...
+
+
+
+
+
+```
+
+The following example shows how to register a listener with a step Java:
+
+Java Configuration
+
+```
+@Bean
+public Step simpleStep() {
+ return this.stepBuilderFactory.get("simpleStep")
+ ...
+ .listener(new ItemFailureLoggerListener())
+ .build();
+}
+```
+
+| |if your listener does anything in an `onError()` method, it must be inside implements ItemProcessor {
+
+ @Override
+ public T process(T item) throws Exception {
+ if (isPoisonPill(item)) {
+ throw new PoisonPillException("Poison pill detected: " + item);
+ }
+ return item;
+ }
+}
+```
+
+Another simple way to stop a step from executing is to return `null` from the`ItemReader`, as shown in the following example:
+
+```
+public class EarlyCompletionItemReader implements ItemReader {
+
+ private ItemReader delegate;
+
+ public void setDelegate(ItemReader delegate) { ... }
+
+ public T read() throws Exception {
+ T item = delegate.read();
+ if (isEndItem(item)) {
+ return null; // end the step here
+ }
+ return item;
+ }
+
+}
+```
+
+The previous example actually relies on the fact that there is a default implementation
+of the `CompletionPolicy` strategy that signals a complete batch when the item to be
+processed is `null`. A more sophisticated completion policy could be implemented and
+injected into the `Step` through the `SimpleStepFactoryBean`.
+
+The following example shows how to inject a completion policy into a step in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+chunk(new SpecialCompletionPolicy())
+ .reader(reader())
+ .writer(writer())
+ .build();
+}
+```
+
+An alternative is to set a flag in the `StepExecution`, which is checked by the `Step`implementations in the framework in between item processing. To implement this
+alternative, we need access to the current `StepExecution`, and this can be achieved by
+implementing a `StepListener` and registering it with the `Step`. The following example
+shows a listener that sets the flag:
+
+```
+public class CustomItemWriter extends ItemListenerSupport implements StepListener {
+
+ private StepExecution stepExecution;
+
+ public void beforeStep(StepExecution stepExecution) {
+ this.stepExecution = stepExecution;
+ }
+
+ public void afterRead(Object item) {
+ if (isPoisonPill(item)) {
+ stepExecution.setTerminateOnly();
+ }
+ }
+
+}
+```
+
+When the flag is set, the default behavior is for the step to throw a`JobInterruptedException`. This behavior can be controlled through the`StepInterruptionPolicy`. However, the only choice is to throw or not throw an exception,
+so this is always an abnormal ending to a job.
+
+### Adding a Footer Record
+
+Often, when writing to flat files, a “footer” record must be appended to the end of the
+file, after all processing has be completed. This can be achieved using the`FlatFileFooterCallback` interface provided by Spring Batch. The `FlatFileFooterCallback`(and its counterpart, the `FlatFileHeaderCallback`) are optional properties of the`FlatFileItemWriter` and can be added to an item writer.
+
+The following example shows how to use the `FlatFileHeaderCallback` and the`FlatFileFooterCallback` in XML:
+
+XML Configuration
+
+```
+
+
+```
+
+The following example shows how to use the `FlatFileHeaderCallback` and the`FlatFileFooterCallback` in Java:
+
+Java Configuration
+
+```
+@Bean
+public FlatFileItemWriter itemWriter(Resource outputResource) {
+ return new FlatFileItemWriterBuilder()
+ .name("itemWriter")
+ .resource(outputResource)
+ .lineAggregator(lineAggregator())
+ .headerCallback(headerCallback())
+ .footerCallback(footerCallback())
+ .build();
+}
+```
+
+The footer callback interface has just one method that is called when the footer must be
+written, as shown in the following interface definition:
+
+```
+public interface FlatFileFooterCallback {
+
+ void writeFooter(Writer writer) throws IOException;
+
+}
+```
+
+#### Writing a Summary Footer
+
+A common requirement involving footer records is to aggregate information during the
+output process and to append this information to the end of the file. This footer often
+serves as a summarization of the file or provides a checksum.
+
+For example, if a batch job is writing `Trade` records to a flat file, and there is a
+requirement that the total amount from all the `Trades` is placed in a footer, then the
+following `ItemWriter` implementation can be used:
+
+```
+public class TradeItemWriter implements ItemWriter,
+ FlatFileFooterCallback {
+
+ private ItemWriter delegate;
+
+ private BigDecimal totalAmount = BigDecimal.ZERO;
+
+ public void write(List items) throws Exception {
+ BigDecimal chunkTotal = BigDecimal.ZERO;
+ for (Trade trade : items) {
+ chunkTotal = chunkTotal.add(trade.getAmount());
+ }
+
+ delegate.write(items);
+
+ // After successfully writing all items
+ totalAmount = totalAmount.add(chunkTotal);
+ }
+
+ public void writeFooter(Writer writer) throws IOException {
+ writer.write("Total Amount Processed: " + totalAmount);
+ }
+
+ public void setDelegate(ItemWriter delegate) {...}
+}
+```
+
+This `TradeItemWriter` stores a `totalAmount` value that is increased with the `amount`from each `Trade` item written. After the last `Trade` is processed, the framework calls`writeFooter`, which puts the `totalAmount` into the file. Note that the `write` method
+makes use of a temporary variable, `chunkTotal`, that stores the total of the`Trade` amounts in the chunk. This is done to ensure that, if a skip occurs in the`write` method, the `totalAmount` is left unchanged. It is only at the end of the `write`method, once we are guaranteed that no exceptions are thrown, that we update the`totalAmount`.
+
+In order for the `writeFooter` method to be called, the `TradeItemWriter` (which
+implements `FlatFileFooterCallback`) must be wired into the `FlatFileItemWriter` as the`footerCallback`.
+
+The following example shows how to wire the `TradeItemWriter` in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+```
+
+The following example shows how to wire the `TradeItemWriter` in Java:
+
+Java Configuration
+
+```
+@Bean
+public TradeItemWriter tradeItemWriter() {
+ TradeItemWriter itemWriter = new TradeItemWriter();
+
+ itemWriter.setDelegate(flatFileItemWriter(null));
+
+ return itemWriter;
+}
+
+@Bean
+public FlatFileItemWriter flatFileItemWriter(Resource outputResource) {
+ return new FlatFileItemWriterBuilder()
+ .name("itemWriter")
+ .resource(outputResource)
+ .lineAggregator(lineAggregator())
+ .footerCallback(tradeItemWriter())
+ .build();
+}
+```
+
+The way that the `TradeItemWriter` has been written so far functions correctly only if
+the `Step` is not restartable. This is because the class is stateful (since it stores the`totalAmount`), but the `totalAmount` is not persisted to the database. Therefore, it
+cannot be retrieved in the event of a restart. In order to make this class restartable,
+the `ItemStream` interface should be implemented along with the methods `open` and`update`, as shown in the following example:
+
+```
+public void open(ExecutionContext executionContext) {
+ if (executionContext.containsKey("total.amount") {
+ totalAmount = (BigDecimal) executionContext.get("total.amount");
+ }
+}
+
+public void update(ExecutionContext executionContext) {
+ executionContext.put("total.amount", totalAmount);
+}
+```
+
+The update method stores the most current version of `totalAmount` to the`ExecutionContext` just before that object is persisted to the database. The open method
+retrieves any existing `totalAmount` from the `ExecutionContext` and uses it as the
+starting point for processing, allowing the `TradeItemWriter` to pick up on restart where
+it left off the previous time the `Step` was run.
+
+### Driving Query Based ItemReaders
+
+In the [chapter on readers and writers](readersAndWriters.html), database input using
+paging was discussed. Many database vendors, such as DB2, have extremely pessimistic
+locking strategies that can cause issues if the table being read also needs to be used by
+other portions of the online application. Furthermore, opening cursors over extremely
+large datasets can cause issues on databases from certain vendors. Therefore, many
+projects prefer to use a 'Driving Query' approach to reading in data. This approach works
+by iterating over keys, rather than the entire object that needs to be returned, as the
+following image illustrates:
+
+
+
+Figure 1. Driving Query Job
+
+As you can see, the example shown in the preceding image uses the same 'FOO' table as was
+used in the cursor-based example. However, rather than selecting the entire row, only the
+IDs were selected in the SQL statement. So, rather than a `FOO` object being returned
+from `read`, an `Integer` is returned. This number can then be used to query for the
+'details', which is a complete `Foo` object, as shown in the following image:
+
+
+
+Figure 2. Driving Query Example
+
+An `ItemProcessor` should be used to transform the key obtained from the driving query
+into a full `Foo` object. An existing DAO can be used to query for the full object based
+on the key.
+
+### Multi-Line Records
+
+While it is usually the case with flat files that each record is confined to a single
+line, it is common that a file might have records spanning multiple lines with multiple
+formats. The following excerpt from a file shows an example of such an arrangement:
+
+```
+HEA;0013100345;2007-02-15
+NCU;Smith;Peter;;T;20014539;F
+BAD;;Oak Street 31/A;;Small Town;00235;IL;US
+FOT;2;2;267.34
+```
+
+Everything between the line starting with 'HEA' and the line starting with 'FOT' is
+considered one record. There are a few considerations that must be made in order to
+handle this situation correctly:
+
+* Instead of reading one record at a time, the `ItemReader` must read every line of the
+ multi-line record as a group, so that it can be passed to the `ItemWriter` intact.
+
+* Each line type may need to be tokenized differently.
+
+Because a single record spans multiple lines and because we may not know how many lines
+there are, the `ItemReader` must be careful to always read an entire record. In order to
+do this, a custom `ItemReader` should be implemented as a wrapper for the`FlatFileItemReader`.
+
+The following example shows how to implement a custom `ItemReader` in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+
+```
+
+The following example shows how to implement a custom `ItemReader` in Java:
+
+Java Configuration
+
+```
+@Bean
+public MultiLineTradeItemReader itemReader() {
+ MultiLineTradeItemReader itemReader = new MultiLineTradeItemReader();
+
+ itemReader.setDelegate(flatFileItemReader());
+
+ return itemReader;
+}
+
+@Bean
+public FlatFileItemReader flatFileItemReader() {
+ FlatFileItemReader reader = new FlatFileItemReaderBuilder<>()
+ .name("flatFileItemReader")
+ .resource(new ClassPathResource("data/iosample/input/multiLine.txt"))
+ .lineTokenizer(orderFileTokenizer())
+ .fieldSetMapper(orderFieldSetMapper())
+ .build();
+ return reader;
+}
+```
+
+To ensure that each line is tokenized properly, which is especially important for
+fixed-length input, the `PatternMatchingCompositeLineTokenizer` can be used on the
+delegate `FlatFileItemReader`. See[`FlatFileItemReader` in the Readers and
+Writers chapter](readersAndWriters.html#flatFileItemReader) for more details. The delegate reader then uses a`PassThroughFieldSetMapper` to deliver a `FieldSet` for each line back to the wrapping`ItemReader`.
+
+The following example shows how to ensure that each line is properly tokenized in XML:
+
+XML Content
+
+```
+
+
+
+
+
+
+```
+
+The following example shows how to ensure that each line is properly tokenized in Java:
+
+Java Content
+
+```
+@Bean
+public PatternMatchingCompositeLineTokenizer orderFileTokenizer() {
+ PatternMatchingCompositeLineTokenizer tokenizer =
+ new PatternMatchingCompositeLineTokenizer();
+
+ Map tokenizers = new HashMap<>(4);
+
+ tokenizers.put("HEA*", headerRecordTokenizer());
+ tokenizers.put("FOT*", footerRecordTokenizer());
+ tokenizers.put("NCU*", customerLineTokenizer());
+ tokenizers.put("BAD*", billingAddressLineTokenizer());
+
+ tokenizer.setTokenizers(tokenizers);
+
+ return tokenizer;
+}
+```
+
+This wrapper has to be able to recognize the end of a record so that it can continually
+call `read()` on its delegate until the end is reached. For each line that is read, the
+wrapper should build up the item to be returned. Once the footer is reached, the item can
+be returned for delivery to the `ItemProcessor` and `ItemWriter`, as shown in the
+following example:
+
+```
+private FlatFileItemReader delegate;
+
+public Trade read() throws Exception {
+ Trade t = null;
+
+ for (FieldSet line = null; (line = this.delegate.read()) != null;) {
+ String prefix = line.readString(0);
+ if (prefix.equals("HEA")) {
+ t = new Trade(); // Record must start with header
+ }
+ else if (prefix.equals("NCU")) {
+ Assert.notNull(t, "No header was found.");
+ t.setLast(line.readString(1));
+ t.setFirst(line.readString(2));
+ ...
+ }
+ else if (prefix.equals("BAD")) {
+ Assert.notNull(t, "No header was found.");
+ t.setCity(line.readString(4));
+ t.setState(line.readString(6));
+ ...
+ }
+ else if (prefix.equals("FOT")) {
+ return t; // Record must end with footer
+ }
+ }
+ Assert.isNull(t, "No 'END' was found.");
+ return null;
+}
+```
+
+### Executing System Commands
+
+Many batch jobs require that an external command be called from within the batch job.
+Such a process could be kicked off separately by the scheduler, but the advantage of
+common metadata about the run would be lost. Furthermore, a multi-step job would also
+need to be split up into multiple jobs as well.
+
+Because the need is so common, Spring Batch provides a `Tasklet` implementation for
+calling system commands.
+
+The following example shows how to call an external command in XML:
+
+XML Configuration
+
+```
+
+
+```
+
+The following example shows how to call an external command in Java:
+
+Java Configuration
+
+```
+@Bean
+public SystemCommandTasklet tasklet() {
+ SystemCommandTasklet tasklet = new SystemCommandTasklet();
+
+ tasklet.setCommand("echo hello");
+ tasklet.setTimeout(5000);
+
+ return tasklet;
+}
+```
+
+### Handling Step Completion When No Input is Found
+
+In many batch scenarios, finding no rows in a database or file to process is not
+exceptional. The `Step` is simply considered to have found no work and completes with 0
+items read. All of the `ItemReader` implementations provided out of the box in Spring
+Batch default to this approach. This can lead to some confusion if nothing is written out
+even when input is present (which usually happens if a file was misnamed or some similar
+issue arises). For this reason, the metadata itself should be inspected to determine how
+much work the framework found to be processed. However, what if finding no input is
+considered exceptional? In this case, programmatically checking the metadata for no items
+processed and causing failure is the best solution. Because this is a common use case,
+Spring Batch provides a listener with exactly this functionality, as shown in
+the class definition for `NoWorkFoundStepExecutionListener`:
+
+```
+public class NoWorkFoundStepExecutionListener extends StepExecutionListenerSupport {
+
+ public ExitStatus afterStep(StepExecution stepExecution) {
+ if (stepExecution.getReadCount() == 0) {
+ return ExitStatus.FAILED;
+ }
+ return null;
+ }
+
+}
+```
+
+The preceding `StepExecutionListener` inspects the `readCount` property of the`StepExecution` during the 'afterStep' phase to determine if no items were read. If that
+is the case, an exit code `FAILED` is returned, indicating that the `Step` should fail.
+Otherwise, `null` is returned, which does not affect the status of the `Step`.
+
+### Passing Data to Future Steps
+
+It is often useful to pass information from one step to another. This can be done through
+the `ExecutionContext`. The catch is that there are two `ExecutionContexts`: one at the`Step` level and one at the `Job` level. The `Step` `ExecutionContext` remains only as
+long as the step, while the `Job` `ExecutionContext` remains through the whole `Job`. On
+the other hand, the `Step` `ExecutionContext` is updated every time the `Step` commits a
+chunk, while the `Job` `ExecutionContext` is updated only at the end of each `Step`.
+
+The consequence of this separation is that all data must be placed in the `Step``ExecutionContext` while the `Step` is executing. Doing so ensures that the data is
+stored properly while the `Step` runs. If data is stored to the `Job` `ExecutionContext`,
+then it is not persisted during `Step` execution. If the `Step` fails, that data is lost.
+
+```
+public class SavingItemWriter implements ItemWriter {
+ private StepExecution stepExecution;
+
+ public void write(List items) throws Exception {
+ // ...
+
+ ExecutionContext stepContext = this.stepExecution.getExecutionContext();
+ stepContext.put("someKey", someObject);
+ }
+
+ @BeforeStep
+ public void saveStepExecution(StepExecution stepExecution) {
+ this.stepExecution = stepExecution;
+ }
+}
+```
+
+To make the data available to future `Steps`, it must be “promoted” to the `Job``ExecutionContext` after the step has finished. Spring Batch provides the`ExecutionContextPromotionListener` for this purpose. The listener must be configured
+with the keys related to the data in the `ExecutionContext` that must be promoted. It can
+also, optionally, be configured with a list of exit code patterns for which the promotion
+should occur (`COMPLETED` is the default). As with all listeners, it must be registered
+on the `Step`.
+
+The following example shows how to promote a step to the `Job` `ExecutionContext` in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+ ...
+
+
+
+
+
+
+ someKey
+
+
+
+```
+
+The following example shows how to promote a step to the `Job` `ExecutionContext` in Java:
+
+Java Configuration
+
+```
+@Bean
+public Job job1() {
+ return this.jobBuilderFactory.get("job1")
+ .start(step1())
+ .next(step1())
+ .build();
+}
+
+@Bean
+public Step step1() {
+ return this.stepBuilderFactory.get("step1")
+ .chunk(10)
+ .reader(reader())
+ .writer(savingWriter())
+ .listener(promotionListener())
+ .build();
+}
+
+@Bean
+public ExecutionContextPromotionListener promotionListener() {
+ ExecutionContextPromotionListener listener = new ExecutionContextPromotionListener();
+
+ listener.setKeys(new String[] {"someKey"});
+
+ return listener;
+}
+```
+
+Finally, the saved values must be retrieved from the `Job` `ExecutionContext`, as shown
+in the following example:
+
+```
+public class RetrievingItemWriter implements ItemWriter {
+ private Object someObject;
+
+ public void write(List items) throws Exception {
+ // ...
+ }
+
+ @BeforeStep
+ public void retrieveInterstepData(StepExecution stepExecution) {
+ JobExecution jobExecution = stepExecution.getJobExecution();
+ ExecutionContext jobContext = jobExecution.getExecutionContext();
+ this.someObject = jobContext.get("someKey");
+ }
+}
+```
\ No newline at end of file
diff --git a/docs/en/spring-batch/domain.md b/docs/en/spring-batch/domain.md
new file mode 100644
index 0000000000000000000000000000000000000000..a424d19cf8a333c5ec076481396d71aa0e5b39d8
--- /dev/null
+++ b/docs/en/spring-batch/domain.md
@@ -0,0 +1,434 @@
+# The Domain Language of Batch
+
+## The Domain Language of Batch
+
+XMLJavaBoth
+
+To any experienced batch architect, the overall concepts of batch processing used in
+Spring Batch should be familiar and comfortable. There are "Jobs" and "Steps" and
+developer-supplied processing units called `ItemReader` and `ItemWriter`. However,
+because of the Spring patterns, operations, templates, callbacks, and idioms, there are
+opportunities for the following:
+
+* Significant improvement in adherence to a clear separation of concerns.
+
+* Clearly delineated architectural layers and services provided as interfaces.
+
+* Simple and default implementations that allow for quick adoption and ease of use
+ out-of-the-box.
+
+* Significantly enhanced extensibility.
+
+The following diagram is a simplified version of the batch reference architecture that
+has been used for decades. It provides an overview of the components that make up the
+domain language of batch processing. This architecture framework is a blueprint that has
+been proven through decades of implementations on the last several generations of
+platforms (COBOL/Mainframe, C/Unix, and now Java/anywhere). JCL and COBOL developers
+are likely to be as comfortable with the concepts as C, C#, and Java developers. Spring
+Batch provides a physical implementation of the layers, components, and technical
+services commonly found in the robust, maintainable systems that are used to address the
+creation of simple to complex batch applications, with the infrastructure and extensions
+to address very complex processing needs.
+
+
+
+Figure 1. Batch Stereotypes
+
+The preceding diagram highlights the key concepts that make up the domain language of
+Spring Batch. A Job has one to many steps, each of which has exactly one `ItemReader`,
+one `ItemProcessor`, and one `ItemWriter`. A job needs to be launched (with`JobLauncher`), and metadata about the currently running process needs to be stored (in`JobRepository`).
+
+### Job
+
+This section describes stereotypes relating to the concept of a batch job. A `Job` is an
+entity that encapsulates an entire batch process. As is common with other Spring
+projects, a `Job` is wired together with either an XML configuration file or Java-based
+configuration. This configuration may be referred to as the "job configuration". However,`Job` is just the top of an overall hierarchy, as shown in the following diagram:
+
+
+
+Figure 2. Job Hierarchy
+
+In Spring Batch, a `Job` is simply a container for `Step` instances. It combines multiple
+steps that belong logically together in a flow and allows for configuration of properties
+global to all steps, such as restartability. The job configuration contains:
+
+* The simple name of the job.
+
+* Definition and ordering of `Step` instances.
+
+* Whether or not the job is restartable.
+
+For those who use Java configuration, Spring Batch provides a default implementation of
+the Job interface in the form of the `SimpleJob` class, which creates some standard
+functionality on top of `Job`. When using java based configuration, a collection of
+builders is made available for the instantiation of a `Job`, as shown in the following
+example:
+
+```
+@Bean
+public Job footballJob() {
+ return this.jobBuilderFactory.get("footballJob")
+ .start(playerLoad())
+ .next(gameLoad())
+ .next(playerSummarization())
+ .build();
+}
+```
+
+For those who use XML configuration, Spring Batch provides a default implementation of the`Job` interface in the form of the `SimpleJob` class, which creates some standard
+functionality on top of `Job`. However, the batch namespace abstracts away the need to
+instantiate it directly. Instead, the `` element can be used, as shown in the
+following example:
+
+```
+
+```
+
+#### JobInstance
+
+A `JobInstance` refers to the concept of a logical job run. Consider a batch job that
+should be run once at the end of the day, such as the 'EndOfDay' `Job` from the preceding
+diagram. There is one 'EndOfDay' job, but each individual run of the `Job` must be
+tracked separately. In the case of this job, there is one logical `JobInstance` per day.
+For example, there is a January 1st run, a January 2nd run, and so on. If the January 1st
+run fails the first time and is run again the next day, it is still the January 1st run.
+(Usually, this corresponds with the data it is processing as well, meaning the January
+1st run processes data for January 1st). Therefore, each `JobInstance` can have multiple
+executions (`JobExecution` is discussed in more detail later in this chapter), and only
+one `JobInstance` corresponding to a particular `Job` and identifying `JobParameters` can
+run at a given time.
+
+The definition of a `JobInstance` has absolutely no bearing on the data to be loaded.
+It is entirely up to the `ItemReader` implementation to determine how data is loaded. For
+example, in the EndOfDay scenario, there may be a column on the data that indicates the
+'effective date' or 'schedule date' to which the data belongs. So, the January 1st run
+would load only data from the 1st, and the January 2nd run would use only data from the
+2nd. Because this determination is likely to be a business decision, it is left up to the`ItemReader` to decide. However, using the same `JobInstance` determines whether or not
+the 'state' (that is, the `ExecutionContext`, which is discussed later in this chapter)
+from previous executions is used. Using a new `JobInstance` means 'start from the
+beginning', and using an existing instance generally means 'start from where you left
+off'.
+
+#### JobParameters
+
+Having discussed `JobInstance` and how it differs from Job, the natural question to ask
+is: "How is one `JobInstance` distinguished from another?" The answer is:`JobParameters`. A `JobParameters` object holds a set of parameters used to start a batch
+job. They can be used for identification or even as reference data during the run, as
+shown in the following image:
+
+
+
+Figure 3. Job Parameters
+
+In the preceding example, where there are two instances, one for January 1st, and another
+for January 2nd, there is really only one `Job`, but it has two `JobParameter` objects:
+one that was started with a job parameter of 01-01-2017 and another that was started with
+a parameter of 01-02-2017. Thus, the contract can be defined as: `JobInstance` = `Job`+ identifying `JobParameters`. This allows a developer to effectively control how a`JobInstance` is defined, since they control what parameters are passed in.
+
+| |Not all job parameters are required to contribute to the identification of a`JobInstance`. By default, they do so. However, the framework also allows the submission` tag, as shown in the following example:
+
+```
+
+
+
+
+
+
+
+
+
+
+```
+
+As long as the batch namespace has been declared, any of its elements can be used. More
+information on configuring a Job can be found in [Configuring and
+Running a Job](job.html#configureJob). More information on configuring a `Step` can be found in[Configuring a Step](step.html#configureStep).
\ No newline at end of file
diff --git a/docs/en/spring-batch/glossary.md b/docs/en/spring-batch/glossary.md
new file mode 100644
index 0000000000000000000000000000000000000000..6f43da1bc4055539a564f5309dd9fc1d8749f638
--- /dev/null
+++ b/docs/en/spring-batch/glossary.md
@@ -0,0 +1,122 @@
+# Glossary
+
+## Appendix A: Glossary
+
+### Spring Batch Glossary
+
+Batch
+
+An accumulation of business transactions over time.
+
+Batch Application Style
+
+Term used to designate batch as an application style in its own right, similar to
+online, Web, or SOA. It has standard elements of input, validation, transformation of
+information to business model, business processing, and output. In addition, it
+requires monitoring at a macro level.
+
+Batch Processing
+
+The handling of a batch of many business transactions that have accumulated over a
+period of time (such as an hour, a day, a week, a month, or a year). It is the
+application of a process or set of processes to many data entities or objects in a
+repetitive and predictable fashion with either no manual element or a separate manual
+element for error processing.
+
+Batch Window
+
+The time frame within which a batch job must complete. This can be constrained by other
+systems coming online, other dependent jobs needing to execute, or other factors
+specific to the batch environment.
+
+Step
+
+The main batch task or unit of work. It initializes the business logic and controls the
+transaction environment, based on commit interval setting and other factors.
+
+Tasklet
+
+A component created by an application developer to process the business logic for a
+Step.
+
+Batch Job Type
+
+Job types describe application of jobs for particular types of processing. Common areas
+are interface processing (typically flat files), forms processing (either for online
+PDF generation or print formats), and report processing.
+
+Driving Query
+
+A driving query identifies the set of work for a job to do. The job then breaks that
+work into individual units of work. For instance, a driving query might be to identify
+all financial transactions that have a status of "pending transmission" and send them
+to a partner system. The driving query returns a set of record IDs to process. Each
+record ID then becomes a unit of work. A driving query may involve a join (if the
+criteria for selection falls across two or more tables) or it may work with a single
+table.
+
+Item
+
+An item represents the smallest amount of complete data for processing. In the simplest
+terms, this might be a line in a file, a row in a database table, or a particular
+element in an XML file.
+
+Logical Unit of Work (LUW)
+
+A batch job iterates through a driving query (or other input source, such as a file) to
+perform the set of work that the job must accomplish. Each iteration of work performed
+is a unit of work.
+
+Commit Interval
+
+A set of LUWs processed within a single transaction.
+
+Partitioning
+
+Splitting a job into multiple threads where each thread is responsible for a subset of
+the overall data to be processed. The threads of execution may be within the same JVM
+or they may span JVMs in a clustered environment that supports workload balancing.
+
+Staging Table
+
+A table that holds temporary data while it is being processed.
+
+Restartable
+
+A job that can be executed again and assumes the same identity as when run initially.
+In other words, it is has the same job instance ID.
+
+Rerunnable
+
+A job that is restartable and manages its own state in terms of the previous run’s
+record processing. An example of a rerunnable step is one based on a driving query. If
+the driving query can be formed so that it limits the processed rows when the job is
+restarted, then it is re-runnable. This is managed by the application logic. Often, a
+condition is added to the `where` statement to limit the rows returned by the driving
+query with logic resembling "and processedFlag!= true".
+
+Repeat
+
+One of the most basic units of batch processing, it defines by repeatability calling a
+portion of code until it is finished and while there is no error. Typically, a batch
+process would be repeatable as long as there is input.
+
+Retry
+
+Simplifies the execution of operations with retry semantics most frequently associated
+with handling transactional output exceptions. Retry is slightly different from repeat,
+rather than continually calling a block of code, retry is stateful and continually
+calls the same block of code with the same input, until it either succeeds or some type
+of retry limit has been exceeded. It is only generally useful when a subsequent
+invocation of the operation might succeed because something in the environment has
+improved.
+
+Recover
+
+Recover operations handle an exception in such a way that a repeat process is able to
+continue.
+
+Skip
+
+Skip is a recovery strategy often used on file input sources as the strategy for
+ignoring bad input records that failed validation.
\ No newline at end of file
diff --git a/docs/en/spring-batch/job.md b/docs/en/spring-batch/job.md
new file mode 100644
index 0000000000000000000000000000000000000000..ebc75c5b814d7c61153d09f216a370c387888796
--- /dev/null
+++ b/docs/en/spring-batch/job.md
@@ -0,0 +1,1357 @@
+# Configuring and Running a Job
+
+## Configuring and Running a Job
+
+XMLJavaBoth
+
+In the [domain section](domain.html#domainLanguageOfBatch) , the overall
+architecture design was discussed, using the following diagram as a
+guide:
+
+
+
+Figure 1. Batch Stereotypes
+
+While the `Job` object may seem like a simple
+container for steps, there are many configuration options of which a
+developer must be aware. Furthermore, there are many considerations for
+how a `Job` will be run and how its meta-data will be
+stored during that run. This chapter will explain the various configuration
+options and runtime concerns of a `Job`.
+
+### Configuring a Job
+
+There are multiple implementations of the [`Job`](#configureJob) interface. However,
+builders abstract away the difference in configuration.
+
+```
+@Bean
+public Job footballJob() {
+ return this.jobBuilderFactory.get("footballJob")
+ .start(playerLoad())
+ .next(gameLoad())
+ .next(playerSummarization())
+ .build();
+}
+```
+
+A `Job` (and typically any `Step` within it) requires a `JobRepository`. The
+configuration of the `JobRepository` is handled via the [`BatchConfigurer`](#javaConfig).
+
+The above example illustrates a `Job` that consists of three `Step` instances. The job related
+builders can also contain other elements that help with parallelisation (`Split`),
+declarative flow control (`Decision`) and externalization of flow definitions (`Flow`).
+
+Whether you use Java or XML, there are multiple implementations of the [`Job`](#configureJob)interface. However, the namespace abstracts away the differences in configuration. It has
+only three required dependencies: a name, `JobRepository` , and a list of `Step` instances.
+
+```
+
+```
+
+The examples here use a parent bean definition to create the steps.
+See the section on [step configuration](step.html#configureStep)for more options declaring specific step details inline. The XML namespace
+defaults to referencing a repository with an id of 'jobRepository', which
+is a sensible default. However, this can be overridden explicitly:
+
+```
+
+```
+
+In addition to steps a job configuration can contain other elements that help with
+parallelization (``), declarative flow control (``) and externalization
+of flow definitions (`
+
+
+
+
+
+
+
+
+```
+
+Please see the section on [Inheriting from a Parent Step](step.html#inheritingFromParentStep)for more detailed information.
+
+#### JobParametersValidator
+
+A job declared in the XML namespace or using any subclass of`AbstractJob` can optionally declare a validator for the job parameters at
+runtime. This is useful when for instance you need to assert that a job
+is started with all its mandatory parameters. There is a`DefaultJobParametersValidator` that can be used to constrain combinations
+of simple mandatory and optional parameters, and for more complex
+constraints you can implement the interface yourself.
+
+The configuration of a validator is supported through the XML namespace through a child
+element of the job, as shown in the following example:
+
+```
+
+
+```
+
+The validator can be specified as a reference (as shown earlier) or as a nested bean
+definition in the beans namespace.
+
+The configuration of a validator is supported through the java builders, as shown in the
+following example:
+
+```
+@Bean
+public Job job1() {
+ return this.jobBuilderFactory.get("job1")
+ .validator(parametersValidator())
+ ...
+ .build();
+}
+```
+
+### Java Config
+
+Spring 3 brought the ability to configure applications via java instead of XML. As of
+Spring Batch 2.2.0, batch jobs can be configured using the same java config.
+There are two components for the java based configuration: the `@EnableBatchProcessing`annotation and two builders.
+
+The `@EnableBatchProcessing` works similarly to the other @Enable\* annotations in the
+Spring family. In this case, `@EnableBatchProcessing` provides a base configuration for
+building batch jobs. Within this base configuration, an instance of `StepScope` is
+created in addition to a number of beans made available to be autowired:
+
+* `JobRepository`: bean name "jobRepository"
+
+* `JobLauncher`: bean name "jobLauncher"
+
+* `JobRegistry`: bean name "jobRegistry"
+
+* `PlatformTransactionManager`: bean name "transactionManager"
+
+* `JobBuilderFactory`: bean name "jobBuilders"
+
+* `StepBuilderFactory`: bean name "stepBuilders"
+
+The core interface for this configuration is the `BatchConfigurer`. The default
+implementation provides the beans mentioned above and requires a `DataSource` as a bean
+within the context to be provided. This data source is used by the JobRepository.
+You can customize any of these beans
+by creating a custom implementation of the `BatchConfigurer` interface.
+Typically, extending the `DefaultBatchConfigurer` (which is provided if a`BatchConfigurer` is not found) and overriding the required getter is sufficient.
+However, implementing your own from scratch may be required. The following
+example shows how to provide a custom transaction manager:
+
+```
+@Bean
+public BatchConfigurer batchConfigurer(DataSource dataSource) {
+ return new DefaultBatchConfigurer(dataSource) {
+ @Override
+ public PlatformTransactionManager getTransactionManager() {
+ return new MyTransactionManager();
+ }
+ };
+}
+```
+
+| |Only one configuration class needs to have the `@EnableBatchProcessing` annotation. Once reader,
+ ItemProcessor processor,
+ ItemWriter writer) {
+ return steps.get("step1")
+ . chunk(10)
+ .reader(reader)
+ .processor(processor)
+ .writer(writer)
+ .build();
+ }
+
+ @Bean
+ protected Step step2(Tasklet tasklet) {
+ return steps.get("step2")
+ .tasklet(tasklet)
+ .build();
+ }
+}
+```
+
+### Configuring a JobRepository
+
+When using `@EnableBatchProcessing`, a `JobRepository` is provided out of the box for you.
+This section addresses configuring your own.
+
+As described in earlier, the [`JobRepository`](#configureJob) is used for basic CRUD operations of the various persisted
+domain objects within Spring Batch, such as`JobExecution` and`StepExecution`. It is required by many of the major
+framework features, such as the `JobLauncher`,`Job`, and `Step`.
+
+The batch namespace abstracts away many of the implementation details of the`JobRepository` implementations and their collaborators. However, there are still a few
+configuration options available, as shown in the following example:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+```
+
+The preceding fragment can be used nearly as is, with almost no changes. Remember also to
+include the appropriate namespace declarations and to make sure spring-tx and spring-aop
+(or the whole of Spring) are on the classpath.
+
+The following example shows how to configure the transactional behavior of the repository
+in Java:
+
+Java Configuration
+
+```
+@Bean
+public TransactionProxyFactoryBean baseProxy() {
+ TransactionProxyFactoryBean transactionProxyFactoryBean = new TransactionProxyFactoryBean();
+ Properties transactionAttributes = new Properties();
+ transactionAttributes.setProperty("*", "PROPAGATION_REQUIRED");
+ transactionProxyFactoryBean.setTransactionAttributes(transactionAttributes);
+ transactionProxyFactoryBean.setTarget(jobRepository());
+ transactionProxyFactoryBean.setTransactionManager(transactionManager());
+ return transactionProxyFactoryBean;
+}
+```
+
+#### Changing the Table Prefix
+
+Another modifiable property of the `JobRepository` is the table prefix of the meta-data
+tables. By default they are all prefaced with `BATCH_`. `BATCH_JOB_EXECUTION` and`BATCH_STEP_EXECUTION` are two examples. However, there are potential reasons to modify this
+prefix. If the schema names needs to be prepended to the table names, or if more than one
+set of meta data tables is needed within the same schema, then the table prefix needs to
+be changed:
+
+The following example shows how to change the table prefix in XML:
+
+XML Configuration
+
+```
+
+
+```
+
+The following example shows the inclusion of `MapJobRepositoryFactoryBean` in Java:
+
+Java Configuration
+
+```
+// This would reside in your BatchConfigurer implementation
+@Override
+protected JobRepository createJobRepository() throws Exception {
+ MapJobRepositoryFactoryBean factory = new MapJobRepositoryFactoryBean();
+ factory.setTransactionManager(transactionManager);
+ return factory.getObject();
+}
+```
+
+Note that the in-memory repository is volatile and so does not allow restart between JVM
+instances. It also cannot guarantee that two job instances with the same parameters are
+launched simultaneously, and is not suitable for use in a multi-threaded Job, or a locally
+partitioned `Step`. So use the database version of the repository wherever you need those
+features.
+
+However it does require a transaction manager to be defined because there are rollback
+semantics within the repository, and because the business logic might still be
+transactional (such as RDBMS access). For testing purposes many people find the`ResourcelessTransactionManager` useful.
+
+| |The `MapJobRepositoryFactoryBean` and related classes have been deprecated in v4 and are scheduled
+
+```
+
+The following example shows how to use `JobRepositoryFactoryBean` to set the database type
+to the closest match in Java:
+
+Java Configuration
+
+```
+// This would reside in your BatchConfigurer implementation
+@Override
+protected JobRepository createJobRepository() throws Exception {
+ JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
+ factory.setDataSource(dataSource);
+ factory.setDatabaseType("db2");
+ factory.setTransactionManager(transactionManager);
+ return factory.getObject();
+}
+```
+
+(The `JobRepositoryFactoryBean` tries to
+auto-detect the database type from the `DataSource`if it is not specified.) The major differences between platforms are
+mainly accounted for by the strategy for incrementing primary keys, so
+often it might be necessary to override the`incrementerFactory` as well (using one of the standard
+implementations from the Spring Framework).
+
+If even that doesn’t work, or you are not using an RDBMS, then the
+only option may be to implement the various `Dao`interfaces that the `SimpleJobRepository` depends
+on and wire one up manually in the normal Spring way.
+
+### Configuring a JobLauncher
+
+When using `@EnableBatchProcessing`, a `JobRegistry` is provided out of the box for you.
+This section addresses configuring your own.
+
+The most basic implementation of the `JobLauncher` interface is the `SimpleJobLauncher`.
+Its only required dependency is a `JobRepository`, in order to obtain an execution.
+
+The following example shows a `SimpleJobLauncher` in XML:
+
+XML Configuration
+
+```
+
+
+```
+
+The following example shows a `SimpleJobLauncher` in Java:
+
+Java Configuration
+
+```
+...
+// This would reside in your BatchConfigurer implementation
+@Override
+protected JobLauncher createJobLauncher() throws Exception {
+ SimpleJobLauncher jobLauncher = new SimpleJobLauncher();
+ jobLauncher.setJobRepository(jobRepository);
+ jobLauncher.afterPropertiesSet();
+ return jobLauncher;
+}
+...
+```
+
+Once a [JobExecution](domain.html#domainLanguageOfBatch) is obtained, it is passed to the
+execute method of `Job`, ultimately returning the `JobExecution` to the caller, as shown
+in the following image:
+
+
+
+Figure 2. Job Launcher Sequence
+
+The sequence is straightforward and works well when launched from a scheduler. However,
+issues arise when trying to launch from an HTTP request. In this scenario, the launching
+needs to be done asynchronously so that the `SimpleJobLauncher` returns immediately to its
+caller. This is because it is not good practice to keep an HTTP request open for the
+amount of time needed by long running processes such as batch. The following image shows
+an example sequence:
+
+
+
+Figure 3. Asynchronous Job Launcher Sequence
+
+The `SimpleJobLauncher` can be configured to allow for this scenario by configuring a`TaskExecutor`.
+
+The following XML example shows a `SimpleJobLauncher` configured to return immediately:
+
+XML Configuration
+
+```
+
+
+
+
+```
+
+The following Java example shows a `SimpleJobLauncher` configured to return immediately:
+
+Java Configuration
+
+```
+@Bean
+public JobLauncher jobLauncher() {
+ SimpleJobLauncher jobLauncher = new SimpleJobLauncher();
+ jobLauncher.setJobRepository(jobRepository());
+ jobLauncher.setTaskExecutor(new SimpleAsyncTaskExecutor());
+ jobLauncher.afterPropertiesSet();
+ return jobLauncher;
+}
+```
+
+Any implementation of the spring `TaskExecutor`interface can be used to control how jobs are asynchronously
+executed.
+
+### Running a Job
+
+At a minimum, launching a batch job requires two things: the`Job` to be launched and a`JobLauncher`. Both can be contained within the same
+context or different contexts. For example, if launching a job from the
+command line, a new JVM will be instantiated for each Job, and thus every
+job will have its own `JobLauncher`. However, if
+running from within a web container within the scope of an`HttpRequest`, there will usually be one`JobLauncher`, configured for asynchronous job
+launching, that multiple requests will invoke to launch their jobs.
+
+#### Running Jobs from the Command Line
+
+For users that want to run their jobs from an enterprise
+scheduler, the command line is the primary interface. This is because
+most schedulers (with the exception of Quartz unless using the
+NativeJob) work directly with operating system
+processes, primarily kicked off with shell scripts. There are many ways
+to launch a Java process besides a shell script, such as Perl, Ruby, or
+even 'build tools' such as ant or maven. However, because most people
+are familiar with shell scripts, this example will focus on them.
+
+##### The CommandLineJobRunner
+
+Because the script launching the job must kick off a Java
+Virtual Machine, there needs to be a class with a main method to act
+as the primary entry point. Spring Batch provides an implementation
+that serves just this purpose:`CommandLineJobRunner`. It’s important to note
+that this is just one way to bootstrap your application, but there are
+many ways to launch a Java process, and this class should in no way be
+viewed as definitive. The `CommandLineJobRunner`performs four tasks:
+
+* Load the appropriate`ApplicationContext`
+
+* Parse command line arguments into`JobParameters`
+
+* Locate the appropriate job based on arguments
+
+* Use the `JobLauncher` provided in the
+ application context to launch the job.
+
+All of these tasks are accomplished using only the arguments
+passed in. The following are required arguments:
+
+|jobPath|The location of the XML file that will be used to
+
+
+
+ getJobInstances(String jobName, int start, int count);
+
+ JobExecution getJobExecution(Long executionId);
+
+ StepExecution getStepExecution(Long jobExecutionId, Long stepExecutionId);
+
+ JobInstance getJobInstance(Long instanceId);
+
+ List getJobExecutions(JobInstance jobInstance);
+
+ Set findRunningJobExecutions(String jobName);
+}
+```
+
+As is evident from the method signatures above, `JobExplorer` is a read-only version of
+the `JobRepository`, and, like the `JobRepository`, it can be easily configured by using a
+factory bean:
+
+The following example shows how to configure a `JobExplorer` in XML:
+
+XML Configuration
+
+```
+
+
+```
+
+The following example shows how to include the `JobRegistryBeanPostProcessor` for a job
+defined in Java:
+
+Java Configuration
+
+```
+@Bean
+public JobRegistryBeanPostProcessor jobRegistryBeanPostProcessor() {
+ JobRegistryBeanPostProcessor postProcessor = new JobRegistryBeanPostProcessor();
+ postProcessor.setJobRegistry(jobRegistry());
+ return postProcessor;
+}
+```
+
+Although it is not strictly necessary, the post-processor in the
+example has been given an id so that it can be included in child
+contexts (e.g. as a parent bean definition) and cause all jobs created
+there to also be registered automatically.
+
+##### `AutomaticJobRegistrar`
+
+This is a lifecycle component that creates child contexts and registers jobs from those
+contexts as they are created. One advantage of doing this is that, while the job names in
+the child contexts still have to be globally unique in the registry, their dependencies
+can have "natural" names. So for example, you can create a set of XML configuration files
+each having only one Job, but all having different definitions of an `ItemReader` with the
+same bean name, such as "reader". If all those files were imported into the same context,
+the reader definitions would clash and override one another, but with the automatic
+registrar this is avoided. This makes it easier to integrate jobs contributed from
+separate modules of an application.
+
+The following example shows how to include the `AutomaticJobRegistrar` for a job defined
+in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+
+```
+
+The following example shows how to include the `AutomaticJobRegistrar` for a job defined
+in Java:
+
+Java Configuration
+
+```
+@Bean
+public AutomaticJobRegistrar registrar() {
+
+ AutomaticJobRegistrar registrar = new AutomaticJobRegistrar();
+ registrar.setJobLoader(jobLoader());
+ registrar.setApplicationContextFactories(applicationContextFactories());
+ registrar.afterPropertiesSet();
+ return registrar;
+
+}
+```
+
+The registrar has two mandatory properties, one is an array of`ApplicationContextFactory` (here created from a
+convenient factory bean), and the other is a`JobLoader`. The `JobLoader`is responsible for managing the lifecycle of the child contexts and
+registering jobs in the `JobRegistry`.
+
+The `ApplicationContextFactory` is
+responsible for creating the child context and the most common usage
+would be as above using a`ClassPathXmlApplicationContextFactory`. One of
+the features of this factory is that by default it copies some of the
+configuration down from the parent context to the child. So for
+instance you don’t have to re-define the`PropertyPlaceholderConfigurer` or AOP
+configuration in the child, if it should be the same as the
+parent.
+
+The `AutomaticJobRegistrar` can be used in
+conjunction with a `JobRegistryBeanPostProcessor`if desired (as long as the `DefaultJobLoader` is
+used as well). For instance this might be desirable if there are jobs
+defined in the main parent context as well as in the child
+locations.
+
+#### JobOperator
+
+As previously discussed, the `JobRepository`provides CRUD operations on the meta-data, and the`JobExplorer` provides read-only operations on the
+meta-data. However, those operations are most useful when used together
+to perform common monitoring tasks such as stopping, restarting, or
+summarizing a Job, as is commonly done by batch operators. Spring Batch
+provides these types of operations via the`JobOperator` interface:
+
+```
+public interface JobOperator {
+
+ List getExecutions(long instanceId) throws NoSuchJobInstanceException;
+
+ List getJobInstances(String jobName, int start, int count)
+ throws NoSuchJobException;
+
+ Set getRunningExecutions(String jobName) throws NoSuchJobException;
+
+ String getParameters(long executionId) throws NoSuchJobExecutionException;
+
+ Long start(String jobName, String parameters)
+ throws NoSuchJobException, JobInstanceAlreadyExistsException;
+
+ Long restart(long executionId)
+ throws JobInstanceAlreadyCompleteException, NoSuchJobExecutionException,
+ NoSuchJobException, JobRestartException;
+
+ Long startNextInstance(String jobName)
+ throws NoSuchJobException, JobParametersNotFoundException, JobRestartException,
+ JobExecutionAlreadyRunningException, JobInstanceAlreadyCompleteException;
+
+ boolean stop(long executionId)
+ throws NoSuchJobExecutionException, JobExecutionNotRunningException;
+
+ String getSummary(long executionId) throws NoSuchJobExecutionException;
+
+ Map getStepExecutionSummaries(long executionId)
+ throws NoSuchJobExecutionException;
+
+ Set getJobNames();
+
+}
+```
+
+The above operations represent methods from many different interfaces, such as`JobLauncher`, `JobRepository`, `JobExplorer`, and `JobRegistry`. For this reason, the
+provided implementation of `JobOperator`, `SimpleJobOperator`, has many dependencies.
+
+The following example shows a typical bean definition for `SimpleJobOperator` in XML:
+
+```
+
+
+
+
+
+
+```
+
+The following example shows a typical bean definition for `SimpleJobOperator` in Java:
+
+```
+ /**
+ * All injected dependencies for this bean are provided by the @EnableBatchProcessing
+ * infrastructure out of the box.
+ */
+ @Bean
+ public SimpleJobOperator jobOperator(JobExplorer jobExplorer,
+ JobRepository jobRepository,
+ JobRegistry jobRegistry) {
+
+ SimpleJobOperator jobOperator = new SimpleJobOperator();
+
+ jobOperator.setJobExplorer(jobExplorer);
+ jobOperator.setJobRepository(jobRepository);
+ jobOperator.setJobRegistry(jobRegistry);
+ jobOperator.setJobLauncher(jobLauncher);
+
+ return jobOperator;
+ }
+```
+
+| |If you set the table prefix on the job repository, don’t forget to set it on the job explorer as well.|
+|---|------------------------------------------------------------------------------------------------------|
+
+#### JobParametersIncrementer
+
+Most of the methods on `JobOperator` are
+self-explanatory, and more detailed explanations can be found on the[javadoc of the interface](https://docs.spring.io/spring-batch/docs/current/api/org/springframework/batch/core/launch/JobOperator.html). However, the`startNextInstance` method is worth noting. This
+method will always start a new instance of a Job.
+This can be extremely useful if there are serious issues in a`JobExecution` and the Job
+needs to be started over again from the beginning. Unlike`JobLauncher` though, which requires a new`JobParameters` object that will trigger a new`JobInstance` if the parameters are different from
+any previous set of parameters, the`startNextInstance` method will use the`JobParametersIncrementer` tied to the`Job` to force the `Job` to a
+new instance:
+
+```
+public interface JobParametersIncrementer {
+
+ JobParameters getNext(JobParameters parameters);
+
+}
+```
+
+The contract of `JobParametersIncrementer` is
+that, given a [JobParameters](#jobParameters)object, it will return the 'next' JobParameters
+object by incrementing any necessary values it may contain. This
+strategy is useful because the framework has no way of knowing what
+changes to the `JobParameters` make it the 'next'
+instance. For example, if the only value in`JobParameters` is a date, and the next instance
+should be created, should that value be incremented by one day? Or one
+week (if the job is weekly for instance)? The same can be said for any
+numerical values that help to identify the Job,
+as shown below:
+
+```
+public class SampleIncrementer implements JobParametersIncrementer {
+
+ public JobParameters getNext(JobParameters parameters) {
+ if (parameters==null || parameters.isEmpty()) {
+ return new JobParametersBuilder().addLong("run.id", 1L).toJobParameters();
+ }
+ long id = parameters.getLong("run.id",1L) + 1;
+ return new JobParametersBuilder().addLong("run.id", id).toJobParameters();
+ }
+}
+```
+
+In this example, the value with a key of 'run.id' is used to
+discriminate between `JobInstances`. If the`JobParameters` passed in is null, it can be
+assumed that the `Job` has never been run before
+and thus its initial state can be returned. However, if not, the old
+value is obtained, incremented by one, and returned.
+
+For jobs defined in XML, an incrementer can be associated with `Job` through the
+'incrementer' attribute in the namespace, as follows:
+
+```
+
+```
+
+For jobs defined in Java, an incrementer can be associated with a 'Job' through the`incrementer` method provided in the builders, as follows:
+
+```
+@Bean
+public Job footballJob() {
+ return this.jobBuilderFactory.get("footballJob")
+ .incrementer(sampleIncrementer())
+ ...
+ .build();
+}
+```
+
+#### Stopping a Job
+
+One of the most common use cases of`JobOperator` is gracefully stopping a
+Job:
+
+```
+Set executions = jobOperator.getRunningExecutions("sampleJob");
+jobOperator.stop(executions.iterator().next());
+```
+
+The shutdown is not immediate, since there is no way to force
+immediate shutdown, especially if the execution is currently in
+developer code that the framework has no control over, such as a
+business service. However, as soon as control is returned back to the
+framework, it will set the status of the current`StepExecution` to`BatchStatus.STOPPED`, save it, then do the same
+for the `JobExecution` before finishing.
+
+#### Aborting a Job
+
+A job execution which is `FAILED` can be
+restarted (if the `Job` is restartable). A job execution whose status is`ABANDONED` will not be restarted by the framework.
+The `ABANDONED` status is also used in step
+executions to mark them as skippable in a restarted job execution: if a
+job is executing and encounters a step that has been marked`ABANDONED` in the previous failed job execution, it
+will move on to the next step (as determined by the job flow definition
+and the step execution exit status).
+
+If the process died (`"kill -9"` or server
+failure) the job is, of course, not running, but the `JobRepository` has
+no way of knowing because no-one told it before the process died. You
+have to tell it manually that you know that the execution either failed
+or should be considered aborted (change its status to`FAILED` or `ABANDONED`) - it’s
+a business decision and there is no way to automate it. Only change the
+status to `FAILED` if it is not restartable, or if
+you know the restart data is valid. There is a utility in Spring Batch
+Admin `JobService` to abort a job execution.
\ No newline at end of file
diff --git a/docs/en/spring-batch/jsr-352.md b/docs/en/spring-batch/jsr-352.md
new file mode 100644
index 0000000000000000000000000000000000000000..6ccea008257b7304321dab4dc28e5e5192dd9ecc
--- /dev/null
+++ b/docs/en/spring-batch/jsr-352.md
@@ -0,0 +1,415 @@
+# JSR-352 Support
+
+## JSR-352 Support
+
+XMLJavaBoth
+
+As of Spring Batch 3.0 support for JSR-352 has been fully implemented. This section is not a replacement for
+the spec itself and instead, intends to explain how the JSR-352 specific concepts apply to Spring Batch.
+Additional information on JSR-352 can be found via the
+JCP here:
+
+### General Notes about Spring Batch and JSR-352
+
+Spring Batch and JSR-352 are structurally the same. They both have jobs that are made up of steps. They
+both have readers, processors, writers, and listeners. However, their interactions are subtly different.
+For example, the `org.springframework.batch.core.SkipListener#onSkipInWrite(S item, Throwable t)`within Spring Batch receives two parameters: the item that was skipped and the Exception that caused the
+skip. The JSR-352 version of the same method
+(`javax.batch.api.chunk.listener.SkipWriteListener#onSkipWriteItem(List items, Exception ex)`)
+also receives two parameters. However the first one is a `List` of all the items
+within the current chunk with the second being the `Exception` that caused the skip.
+Because of these differences, it is important to note that there are two paths to execute a job within
+Spring Batch: either a traditional Spring Batch job or a JSR-352 based job. While the use of Spring Batch
+artifacts (readers, writers, etc) will work within a job configured with JSR-352’s JSL and executed with the`JsrJobOperator`, they will behave according to the rules of JSR-352. It is also
+important to note that batch artifacts that have been developed against the JSR-352 interfaces will not work
+within a traditional Spring Batch job.
+
+### Setup
+
+#### Application Contexts
+
+All JSR-352 based jobs within Spring Batch consist of two application contexts. A parent context, that
+contains beans related to the infrastructure of Spring Batch such as the `JobRepository`,`PlatformTransactionManager`, etc and a child context that consists of the configuration
+of the job to be run. The parent context is defined via the `jsrBaseContext.xml` provided
+by the framework. This context may be overridden by setting the `JSR-352-BASE-CONTEXT` system
+property.
+
+| |The base context is not processed by the JSR-352 processors for things like property injection so
+
+
+
+
+
+
+
+
+
+
+
+```
+
+The following example shows how to use Spring dependency injection within a JSR-352 based
+batch job in Java:
+
+Java Configuration
+
+```
+@Configuration
+public class BatchConfiguration {
+
+ @Bean
+ public Batchlet fooBatchlet() {
+ FooBatchlet batchlet = new FooBatchlet();
+ batchlet.setProp("bar");
+ return batchlet;
+ }
+}
+
+
+
+
+
+
+```
+
+The assembly of Spring contexts (imports, etc) works with JSR-352 jobs just as it would with any other
+Spring based application. The only difference with a JSR-352 based job is that the entry point for the
+context definition will be the job definition found in /META-INF/batch-jobs/.
+
+To use the thread context class loader approach, all you need to do is provide the fully qualified class
+name as the ref. It is important to note that when using this approach or the `batch.xml` approach, the class
+referenced requires a no argument constructor which will be used to create the bean.
+
+```
+
+
+
+
+
+```
+
+### Batch Properties
+
+#### Property Support
+
+JSR-352 allows for properties to be defined at the Job, Step and batch artifact level by way of
+configuration in the JSL. Batch properties are configured at each level in the following way:
+
+```
+
+
+```
+
+`Properties` may be configured on any batch artifact.
+
+#### @BatchProperty annotation
+
+`Properties` are referenced in batch artifacts by annotating class fields with the`@BatchProperty` and `@Inject` annotations (both annotations
+are required by the spec). As defined by JSR-352, fields for properties must be String typed. Any type
+conversion is up to the implementing developer to perform.
+
+An `javax.batch.api.chunk.ItemReader` artifact could be configured with a
+properties block such as the one described above and accessed as such:
+
+```
+public class MyItemReader extends AbstractItemReader {
+ @Inject
+ @BatchProperty
+ private String propertyName1;
+
+ ...
+}
+```
+
+The value of the field "propertyName1" will be "propertyValue1"
+
+#### Property Substitution
+
+Property substitution is provided by way of operators and simple conditional expressions. The general
+usage is `#{operator['key']}`.
+
+Supported operators:
+
+* `jobParameters`: access job parameter values that the job was started/restarted with.
+
+* `jobProperties`: access properties configured at the job level of the JSL.
+
+* `systemProperties`: access named system properties.
+
+* `partitionPlan`: access named property from the partition plan of a partitioned step.
+
+```
+#{jobParameters['unresolving.prop']}?:#{systemProperties['file.separator']}
+```
+
+The left hand side of the assignment is the expected value, the right hand side is the
+default value. In the preceding
+example, the result will resolve to a value of the system property file.separator as
+#{jobParameters['unresolving.prop']} is assumed to not be resolvable. If neither
+expressions can be resolved, an empty String will be returned. Multiple conditions can be
+used, which are separated by a ';'.
+
+### Processing Models
+
+JSR-352 provides the same two basic processing models that Spring Batch does:
+
+* Item based processing - Using an `javax.batch.api.chunk.ItemReader`, an optional`javax.batch.api.chunk.ItemProcessor`, and an `javax.batch.api.chunk.ItemWriter`.
+
+* Task based processing - Using a `javax.batch.api.Batchlet`implementation. This processing model is the same as the`org.springframework.batch.core.step.tasklet.Tasklet` based processing
+ currently available.
+
+#### Item based processing
+
+Item based processing in this context is a chunk size being set by the number of items read by an`ItemReader`. To configure a step this way, specify the`item-count` (which defaults to 10) and optionally configure the`checkpoint-policy` as item (this is the default).
+
+```
+...
+
+
+
+
+...
+```
+
+If item-based checkpointing is chosen, an additional attribute `time-limit` is supported.
+This sets a time limit for how long the number of items specified has to be processed. If
+the timeout is reached, the chunk will complete with however many items have been read by
+then regardless of what the `item-count` is configured to be.
+
+#### Custom checkpointing
+
+JSR-352 calls the process around the commit interval within a step "checkpointing".
+Item-based checkpointing is one approach as mentioned above. However, this is not robust
+enough in many cases. Because of this, the spec allows for the implementation of a custom
+checkpointing algorithm by implementing the `javax.batch.api.chunk.CheckpointAlgorithm`interface. This functionality is functionally the same as Spring Batch’s custom completion
+policy. To use an implementation of `CheckpointAlgorithm`, configure your step with the
+custom `checkpoint-policy` as shown below where `fooCheckpointer` refers to an
+implementation of `CheckpointAlgorithm`.
+
+```
+...
+
+
+
+
+...
+```
+
+### Running a job
+
+The entrance to executing a JSR-352 based job is through the`javax.batch.operations.JobOperator`. Spring Batch provides its own implementation of
+this interface (`org.springframework.batch.core.jsr.launch.JsrJobOperator`). This
+implementation is loaded via the `javax.batch.runtime.BatchRuntime`. Launching a
+JSR-352 based batch job is implemented as follows:
+
+```
+JobOperator jobOperator = BatchRuntime.getJobOperator();
+long jobExecutionId = jobOperator.start("fooJob", new Properties());
+```
+
+The above code does the following:
+
+* Bootstraps a base `ApplicationContext`: In order to provide batch functionality, the
+ framework needs some infrastructure bootstrapped. This occurs once per JVM. The
+ components that are bootstrapped are similar to those provided by`@EnableBatchProcessing`. Specific details can be found in the javadoc for the`JsrJobOperator`.
+
+* Loads an `ApplicationContext` for the job requested: In the example
+ above, the framework looks in /META-INF/batch-jobs for a file named fooJob.xml and load a
+ context that is a child of the shared context mentioned previously.
+
+* Launch the job: The job defined within the context will be executed asynchronously.
+ The `JobExecution’s` ID will be returned.
+
+| |All JSR-352 based batch jobs are executed asynchronously.|
+|---|---------------------------------------------------------|
+
+When `JobOperator#start` is called using `SimpleJobOperator`, Spring Batch determines if
+the call is an initial run or a retry of a previously executed run. Using the JSR-352
+based `JobOperator#start(String jobXMLName, Properties jobParameters)`, the framework
+will always create a new JobInstance (JSR-352 job parameters are non-identifying). In order to
+restart a job, a call to`JobOperator#restart(long executionId, Properties restartParameters)` is required.
+
+### Contexts
+
+JSR-352 defines two context objects that are used to interact with the meta-data of a job or step from
+within a batch artifact: `javax.batch.runtime.context.JobContext` and`javax.batch.runtime.context.StepContext`. Both of these are available in any step
+level artifact (`Batchlet`, `ItemReader`, etc) with the`JobContext` being available to job level artifacts as well
+(`JobListener` for example).
+
+To obtain a reference to the `JobContext` or `StepContext`within the current scope, simply use the `@Inject` annotation:
+
+```
+@Inject
+JobContext jobContext;
+```
+
+| |@Autowire for JSR-352 contexts implements ItemWriter {
+
+ ItemWriter itemWriter;
+
+ public CompositeItemWriter(ItemWriter itemWriter) {
+ this.itemWriter = itemWriter;
+ }
+
+ public void write(List items) throws Exception {
+ //Add business logic here
+ itemWriter.write(items);
+ }
+
+ public void setDelegate(ItemWriter itemWriter){
+ this.itemWriter = itemWriter;
+ }
+}
+```
+
+The preceding class contains another `ItemWriter` to which it delegates after having
+provided some business logic. This pattern could easily be used for an `ItemReader` as
+well, perhaps to obtain more reference data based upon the input that was provided by the
+main `ItemReader`. It is also useful if you need to control the call to `write` yourself.
+However, if you only want to 'transform' the item passed in for writing before it is
+actually written, you need not `write` yourself. You can just modify the item. For this
+scenario, Spring Batch provides the `ItemProcessor` interface, as shown in the following
+interface definition:
+
+```
+public interface ItemProcessor {
+
+ O process(I item) throws Exception;
+}
+```
+
+An `ItemProcessor` is simple. Given one object, transform it and return another. The
+provided object may or may not be of the same type. The point is that business logic may
+be applied within the process, and it is completely up to the developer to create that
+logic. An `ItemProcessor` can be wired directly into a step. For example, assume an`ItemReader` provides a class of type `Foo` and that it needs to be converted to type `Bar`before being written out. The following example shows an `ItemProcessor` that performs
+the conversion:
+
+```
+public class Foo {}
+
+public class Bar {
+ public Bar(Foo foo) {}
+}
+
+public class FooProcessor implements ItemProcessor {
+ public Bar process(Foo foo) throws Exception {
+ //Perform simple transformation, convert a Foo to a Bar
+ return new Bar(foo);
+ }
+}
+
+public class BarWriter implements ItemWriter {
+ public void write(List bars) throws Exception {
+ //write bars
+ }
+}
+```
+
+In the preceding example, there is a class `Foo`, a class `Bar`, and a class`FooProcessor` that adheres to the `ItemProcessor` interface. The transformation is
+simple, but any type of transformation could be done here. The `BarWriter` writes `Bar`objects, throwing an exception if any other type is provided. Similarly, the`FooProcessor` throws an exception if anything but a `Foo` is provided. The`FooProcessor` can then be injected into a `Step`, as shown in the following example:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+```
+
+Java Configuration
+
+```
+@Bean
+public Job ioSampleJob() {
+ return this.jobBuilderFactory.get("ioSampleJob")
+ .start(step1())
+ .build();
+}
+
+@Bean
+public Step step1() {
+ return this.stepBuilderFactory.get("step1")
+ .chunk(2)
+ .reader(fooReader())
+ .processor(fooProcessor())
+ .writer(barWriter())
+ .build();
+}
+```
+
+A difference between `ItemProcessor` and `ItemReader` or `ItemWriter` is that an `ItemProcessor`is optional for a `Step`.
+
+### Chaining ItemProcessors
+
+Performing a single transformation is useful in many scenarios, but what if you want to
+'chain' together multiple `ItemProcessor` implementations? This can be accomplished using
+the composite pattern mentioned previously. To update the previous, single
+transformation, example, `Foo` is transformed to `Bar`, which is transformed to `Foobar`and written out, as shown in the following example:
+
+```
+public class Foo {}
+
+public class Bar {
+ public Bar(Foo foo) {}
+}
+
+public class Foobar {
+ public Foobar(Bar bar) {}
+}
+
+public class FooProcessor implements ItemProcessor {
+ public Bar process(Foo foo) throws Exception {
+ //Perform simple transformation, convert a Foo to a Bar
+ return new Bar(foo);
+ }
+}
+
+public class BarProcessor implements ItemProcessor {
+ public Foobar process(Bar bar) throws Exception {
+ return new Foobar(bar);
+ }
+}
+
+public class FoobarWriter implements ItemWriter{
+ public void write(List items) throws Exception {
+ //write items
+ }
+}
+```
+
+A `FooProcessor` and a `BarProcessor` can be 'chained' together to give the resultant`Foobar`, as shown in the following example:
+
+```
+CompositeItemProcessor compositeProcessor =
+ new CompositeItemProcessor();
+List itemProcessors = new ArrayList();
+itemProcessors.add(new FooProcessor());
+itemProcessors.add(new BarProcessor());
+compositeProcessor.setDelegates(itemProcessors);
+```
+
+Just as with the previous example, the composite processor can be configured into the`Step`:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+
+
+
+
+```
+
+Java Configuration
+
+```
+@Bean
+public Job ioSampleJob() {
+ return this.jobBuilderFactory.get("ioSampleJob")
+ .start(step1())
+ .build();
+}
+
+@Bean
+public Step step1() {
+ return this.stepBuilderFactory.get("step1")
+ .chunk(2)
+ .reader(fooReader())
+ .processor(compositeProcessor())
+ .writer(foobarWriter())
+ .build();
+}
+
+@Bean
+public CompositeItemProcessor compositeProcessor() {
+ List delegates = new ArrayList<>(2);
+ delegates.add(new FooProcessor());
+ delegates.add(new BarProcessor());
+
+ CompositeItemProcessor processor = new CompositeItemProcessor();
+
+ processor.setDelegates(delegates);
+
+ return processor;
+}
+```
+
+### Filtering Records
+
+One typical use for an item processor is to filter out records before they are passed to
+the `ItemWriter`. Filtering is an action distinct from skipping. Skipping indicates that
+a record is invalid, while filtering simply indicates that a record should not be
+written.
+
+For example, consider a batch job that reads a file containing three different types of
+records: records to insert, records to update, and records to delete. If record deletion
+is not supported by the system, then we would not want to send any "delete" records to
+the `ItemWriter`. But, since these records are not actually bad records, we would want to
+filter them out rather than skip them. As a result, the `ItemWriter` would receive only
+"insert" and "update" records.
+
+To filter a record, you can return `null` from the `ItemProcessor`. The framework detects
+that the result is `null` and avoids adding that item to the list of records delivered to
+the `ItemWriter`. As usual, an exception thrown from the `ItemProcessor` results in a
+skip.
+
+### Validating Input
+
+In the [ItemReaders and ItemWriters](readersAndWriters.html#readersAndWriters) chapter, multiple approaches to parsing input have been
+discussed. Each major implementation throws an exception if it is not 'well-formed'. The`FixedLengthTokenizer` throws an exception if a range of data is missing. Similarly,
+attempting to access an index in a `RowMapper` or `FieldSetMapper` that does not exist or
+is in a different format than the one expected causes an exception to be thrown. All of
+these types of exceptions are thrown before `read` returns. However, they do not address
+the issue of whether or not the returned item is valid. For example, if one of the fields
+is an age, it obviously cannot be negative. It may parse correctly, because it exists and
+is a number, but it does not cause an exception. Since there are already a plethora of
+validation frameworks, Spring Batch does not attempt to provide yet another. Rather, it
+provides a simple interface, called `Validator`, that can be implemented by any number of
+frameworks, as shown in the following interface definition:
+
+```
+public interface Validator {
+
+ void validate(T value) throws ValidationException;
+
+}
+```
+
+The contract is that the `validate` method throws an exception if the object is invalid
+and returns normally if it is valid. Spring Batch provides an out of the box`ValidatingItemProcessor`, as shown in the following bean definition:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+```
+
+Java Configuration
+
+```
+@Bean
+public ValidatingItemProcessor itemProcessor() {
+ ValidatingItemProcessor processor = new ValidatingItemProcessor();
+
+ processor.setValidator(validator());
+
+ return processor;
+}
+
+@Bean
+public SpringValidator validator() {
+ SpringValidator validator = new SpringValidator();
+
+ validator.setValidator(new TradeValidator());
+
+ return validator;
+}
+```
+
+You can also use the `BeanValidatingItemProcessor` to validate items annotated with
+the Bean Validation API (JSR-303) annotations. For example, given the following type `Person`:
+
+```
+class Person {
+
+ @NotEmpty
+ private String name;
+
+ public Person(String name) {
+ this.name = name;
+ }
+
+ public String getName() {
+ return name;
+ }
+
+ public void setName(String name) {
+ this.name = name;
+ }
+
+}
+```
+
+you can validate items by declaring a `BeanValidatingItemProcessor` bean in your
+application context and register it as a processor in your chunk-oriented step:
+
+```
+@Bean
+public BeanValidatingItemProcessor beanValidatingItemProcessor() throws Exception {
+ BeanValidatingItemProcessor beanValidatingItemProcessor = new BeanValidatingItemProcessor<>();
+ beanValidatingItemProcessor.setFilter(true);
+
+ return beanValidatingItemProcessor;
+}
+```
+
+### Fault Tolerance
+
+When a chunk is rolled back, items that have been cached during reading may be
+reprocessed. If a step is configured to be fault tolerant (typically by using skip or
+retry processing), any `ItemProcessor` used should be implemented in a way that is
+idempotent. Typically that would consist of performing no changes on the input item for
+the `ItemProcessor` and only updating the
+instance that is the result.
\ No newline at end of file
diff --git a/docs/en/spring-batch/readersAndWriters.md b/docs/en/spring-batch/readersAndWriters.md
new file mode 100644
index 0000000000000000000000000000000000000000..9d7cea907527e6ba3b545ee92acd63df1e2088aa
--- /dev/null
+++ b/docs/en/spring-batch/readersAndWriters.md
@@ -0,0 +1,2760 @@
+# ItemReaders and ItemWriters
+
+## ItemReaders and ItemWriters
+
+XMLJavaBoth
+
+All batch processing can be described in its most simple form as reading in large amounts
+of data, performing some type of calculation or transformation, and writing the result
+out. Spring Batch provides three key interfaces to help perform bulk reading and writing:`ItemReader`, `ItemProcessor`, and `ItemWriter`.
+
+### `ItemReader`
+
+Although a simple concept, an `ItemReader` is the means for providing data from many
+different types of input. The most general examples include:
+
+* Flat File: Flat-file item readers read lines of data from a flat file that typically
+ describes records with fields of data defined by fixed positions in the file or delimited
+ by some special character (such as a comma).
+
+* XML: XML `ItemReaders` process XML independently of technologies used for parsing,
+ mapping and validating objects. Input data allows for the validation of an XML file
+ against an XSD schema.
+
+* Database: A database resource is accessed to return resultsets which can be mapped to
+ objects for processing. The default SQL `ItemReader` implementations invoke a `RowMapper`to return objects, keep track of the current row if restart is required, store basic
+ statistics, and provide some transaction enhancements that are explained later.
+
+There are many more possibilities, but we focus on the basic ones for this chapter. A
+complete list of all available `ItemReader` implementations can be found in[Appendix A](appendix.html#listOfReadersAndWriters).
+
+`ItemReader` is a basic interface for generic
+input operations, as shown in the following interface definition:
+
+```
+public interface ItemReader {
+
+ T read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException;
+
+}
+```
+
+The `read` method defines the most essential contract of the `ItemReader`. Calling it
+returns one item or `null` if no more items are left. An item might represent a line in a
+file, a row in a database, or an element in an XML file. It is generally expected that
+these are mapped to a usable domain object (such as `Trade`, `Foo`, or others), but there
+is no requirement in the contract to do so.
+
+It is expected that implementations of the `ItemReader` interface are forward only.
+However, if the underlying resource is transactional (such as a JMS queue) then calling`read` may return the same logical item on subsequent calls in a rollback scenario. It is
+also worth noting that a lack of items to process by an `ItemReader` does not cause an
+exception to be thrown. For example, a database `ItemReader` that is configured with a
+query that returns 0 results returns `null` on the first invocation of `read`.
+
+### `ItemWriter`
+
+`ItemWriter` is similar in functionality to an `ItemReader` but with inverse operations.
+Resources still need to be located, opened, and closed but they differ in that an`ItemWriter` writes out, rather than reading in. In the case of databases or queues,
+these operations may be inserts, updates, or sends. The format of the serialization of
+the output is specific to each batch job.
+
+As with `ItemReader`,`ItemWriter` is a fairly generic interface, as shown in the following interface definition:
+
+```
+public interface ItemWriter {
+
+ void write(List items) throws Exception;
+
+}
+```
+
+As with `read` on `ItemReader`, `write` provides the basic contract of `ItemWriter`. It
+attempts to write out the list of items passed in as long as it is open. Because it is
+generally expected that items are 'batched' together into a chunk and then output, the
+interface accepts a list of items, rather than an item by itself. After writing out the
+list, any flushing that may be necessary can be performed before returning from the write
+method. For example, if writing to a Hibernate DAO, multiple calls to write can be made,
+one for each item. The writer can then call `flush` on the hibernate session before
+returning.
+
+### `ItemStream`
+
+Both `ItemReaders` and `ItemWriters` serve their individual purposes well, but there is a
+common concern among both of them that necessitates another interface. In general, as
+part of the scope of a batch job, readers and writers need to be opened, closed, and
+require a mechanism for persisting state. The `ItemStream` interface serves that purpose,
+as shown in the following example:
+
+```
+public interface ItemStream {
+
+ void open(ExecutionContext executionContext) throws ItemStreamException;
+
+ void update(ExecutionContext executionContext) throws ItemStreamException;
+
+ void close() throws ItemStreamException;
+}
+```
+
+Before describing each method, we should mention the `ExecutionContext`. Clients of an`ItemReader` that also implement `ItemStream` should call `open` before any calls to`read`, in order to open any resources such as files or to obtain connections. A similar
+restriction applies to an `ItemWriter` that implements `ItemStream`. As mentioned in
+Chapter 2, if expected data is found in the `ExecutionContext`, it may be used to start
+the `ItemReader` or `ItemWriter` at a location other than its initial state. Conversely,`close` is called to ensure that any resources allocated during open are released safely.`update` is called primarily to ensure that any state currently being held is loaded into
+the provided `ExecutionContext`. This method is called before committing, to ensure that
+the current state is persisted in the database before commit.
+
+In the special case where the client of an `ItemStream` is a `Step` (from the Spring
+Batch Core), an `ExecutionContext` is created for each StepExecution to allow users to
+store the state of a particular execution, with the expectation that it is returned if
+the same `JobInstance` is started again. For those familiar with Quartz, the semantics
+are very similar to a Quartz `JobDataMap`.
+
+### The Delegate Pattern and Registering with the Step
+
+Note that the `CompositeItemWriter` is an example of the delegation pattern, which is
+common in Spring Batch. The delegates themselves might implement callback interfaces,
+such as `StepListener`. If they do and if they are being used in conjunction with Spring
+Batch Core as part of a `Step` in a `Job`, then they almost certainly need to be
+registered manually with the `Step`. A reader, writer, or processor that is directly
+wired into the `Step` gets registered automatically if it implements `ItemStream` or a`StepListener` interface. However, because the delegates are not known to the `Step`,
+they need to be injected as listeners or streams (or both if appropriate).
+
+The following example shows how to inject a delegate as a stream in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+chunk(2)
+ .reader(fooReader())
+ .processor(fooProcessor())
+ .writer(compositeItemWriter())
+ .stream(barWriter())
+ .build();
+}
+
+@Bean
+public CustomCompositeItemWriter compositeItemWriter() {
+
+ CustomCompositeItemWriter writer = new CustomCompositeItemWriter();
+
+ writer.setDelegate(barWriter());
+
+ return writer;
+}
+
+@Bean
+public BarWriter barWriter() {
+ return new BarWriter();
+}
+```
+
+### Flat Files
+
+One of the most common mechanisms for interchanging bulk data has always been the flat
+file. Unlike XML, which has an agreed upon standard for defining how it is structured
+(XSD), anyone reading a flat file must understand ahead of time exactly how the file is
+structured. In general, all flat files fall into two types: delimited and fixed length.
+Delimited files are those in which fields are separated by a delimiter, such as a comma.
+Fixed Length files have fields that are a set length.
+
+#### The `FieldSet`
+
+When working with flat files in Spring Batch, regardless of whether it is for input or
+output, one of the most important classes is the `FieldSet`. Many architectures and
+libraries contain abstractions for helping you read in from a file, but they usually
+return a `String` or an array of `String` objects. This really only gets you halfway
+there. A `FieldSet` is Spring Batch’s abstraction for enabling the binding of fields from
+a file resource. It allows developers to work with file input in much the same way as
+they would work with database input. A `FieldSet` is conceptually similar to a JDBC`ResultSet`. A `FieldSet` requires only one argument: a `String` array of tokens.
+Optionally, you can also configure the names of the fields so that the fields may be
+accessed either by index or name as patterned after `ResultSet`, as shown in the following
+example:
+
+```
+String[] tokens = new String[]{"foo", "1", "true"};
+FieldSet fs = new DefaultFieldSet(tokens);
+String name = fs.readString(0);
+int value = fs.readInt(1);
+boolean booleanValue = fs.readBoolean(2);
+```
+
+There are many more options on the `FieldSet` interface, such as `Date`, long,`BigDecimal`, and so on. The biggest advantage of the `FieldSet` is that it provides
+consistent parsing of flat file input. Rather than each batch job parsing differently in
+potentially unexpected ways, it can be consistent, both when handling errors caused by a
+format exception, or when doing simple data conversions.
+
+#### `FlatFileItemReader`
+
+A flat file is any type of file that contains at most two-dimensional (tabular) data.
+Reading flat files in the Spring Batch framework is facilitated by the class called`FlatFileItemReader`, which provides basic functionality for reading and parsing flat
+files. The two most important required dependencies of `FlatFileItemReader` are`Resource` and `LineMapper`. The `LineMapper` interface is explored more in the next
+sections. The resource property represents a Spring Core `Resource`. Documentation
+explaining how to create beans of this type can be found in[Spring
+Framework, Chapter 5. Resources](https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#resources). Therefore, this guide does not go into the details of
+creating `Resource` objects beyond showing the following simple example:
+
+```
+Resource resource = new FileSystemResource("resources/trades.csv");
+```
+
+In complex batch environments, the directory structures are often managed by the Enterprise Application Integration (EAI)
+infrastructure, where drop zones for external interfaces are established for moving files
+from FTP locations to batch processing locations and vice versa. File moving utilities
+are beyond the scope of the Spring Batch architecture, but it is not unusual for batch
+job streams to include file moving utilities as steps in the job stream. The batch
+architecture only needs to know how to locate the files to be processed. Spring Batch
+begins the process of feeding the data into the pipe from this starting point. However,[Spring Integration](https://projects.spring.io/spring-integration/) provides many
+of these types of services.
+
+The other properties in `FlatFileItemReader` let you further specify how your data is
+interpreted, as described in the following table:
+
+| Property | Type | Description |
+|---------------------|---------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| comments | String[] | Specifies line prefixes that indicate comment rows. |
+| encoding | String | Specifies what text encoding to use. The default is the value of `Charset.defaultCharset()`. |
+| lineMapper | `LineMapper` | Converts a `String` to an `Object` representing the item. |
+| linesToSkip | int | Number of lines to ignore at the top of the file. |
+|recordSeparatorPolicy|RecordSeparatorPolicy| Used to determine where the line endings are {
+
+ T mapLine(String line, int lineNumber) throws Exception;
+
+}
+```
+
+The basic contract is that, given the current line and the line number with which it is
+associated, the mapper should return a resulting domain object. This is similar to`RowMapper`, in that each line is associated with its line number, just as each row in a`ResultSet` is tied to its row number. This allows the line number to be tied to the
+resulting domain object for identity comparison or for more informative logging. However,
+unlike `RowMapper`, the `LineMapper` is given a raw line which, as discussed above, only
+gets you halfway there. The line must be tokenized into a `FieldSet`, which can then be
+mapped to an object, as described later in this document.
+
+##### `LineTokenizer`
+
+An abstraction for turning a line of input into a `FieldSet` is necessary because there
+can be many formats of flat file data that need to be converted to a `FieldSet`. In
+Spring Batch, this interface is the `LineTokenizer`:
+
+```
+public interface LineTokenizer {
+
+ FieldSet tokenize(String line);
+
+}
+```
+
+The contract of a `LineTokenizer` is such that, given a line of input (in theory the`String` could encompass more than one line), a `FieldSet` representing the line is
+returned. This `FieldSet` can then be passed to a `FieldSetMapper`. Spring Batch contains
+the following `LineTokenizer` implementations:
+
+* `DelimitedLineTokenizer`: Used for files where fields in a record are separated by a
+ delimiter. The most common delimiter is a comma, but pipes or semicolons are often used
+ as well.
+
+* `FixedLengthTokenizer`: Used for files where fields in a record are each a "fixed
+ width". The width of each field must be defined for each record type.
+
+* `PatternMatchingCompositeLineTokenizer`: Determines which `LineTokenizer` among a list of
+ tokenizers should be used on a particular line by checking against a pattern.
+
+##### `FieldSetMapper`
+
+The `FieldSetMapper` interface defines a single method, `mapFieldSet`, which takes a`FieldSet` object and maps its contents to an object. This object may be a custom DTO, a
+domain object, or an array, depending on the needs of the job. The `FieldSetMapper` is
+used in conjunction with the `LineTokenizer` to translate a line of data from a resource
+into an object of the desired type, as shown in the following interface definition:
+
+```
+public interface FieldSetMapper {
+
+ T mapFieldSet(FieldSet fieldSet) throws BindException;
+
+}
+```
+
+The pattern used is the same as the `RowMapper` used by `JdbcTemplate`.
+
+##### `DefaultLineMapper`
+
+Now that the basic interfaces for reading in flat files have been defined, it becomes
+clear that three basic steps are required:
+
+1. Read one line from the file.
+
+2. Pass the `String` line into the `LineTokenizer#tokenize()` method to retrieve a`FieldSet`.
+
+3. Pass the `FieldSet` returned from tokenizing to a `FieldSetMapper`, returning the
+ result from the `ItemReader#read()` method.
+
+The two interfaces described above represent two separate tasks: converting a line into a`FieldSet` and mapping a `FieldSet` to a domain object. Because the input of a`LineTokenizer` matches the input of the `LineMapper` (a line), and the output of a`FieldSetMapper` matches the output of the `LineMapper`, a default implementation that
+uses both a `LineTokenizer` and a `FieldSetMapper` is provided. The `DefaultLineMapper`,
+shown in the following class definition, represents the behavior most users need:
+
+```
+public class DefaultLineMapper implements LineMapper<>, InitializingBean {
+
+ private LineTokenizer tokenizer;
+
+ private FieldSetMapper fieldSetMapper;
+
+ public T mapLine(String line, int lineNumber) throws Exception {
+ return fieldSetMapper.mapFieldSet(tokenizer.tokenize(line));
+ }
+
+ public void setLineTokenizer(LineTokenizer tokenizer) {
+ this.tokenizer = tokenizer;
+ }
+
+ public void setFieldSetMapper(FieldSetMapper fieldSetMapper) {
+ this.fieldSetMapper = fieldSetMapper;
+ }
+}
+```
+
+The above functionality is provided in a default implementation, rather than being built
+into the reader itself (as was done in previous versions of the framework) to allow users
+greater flexibility in controlling the parsing process, especially if access to the raw
+line is needed.
+
+##### Simple Delimited File Reading Example
+
+The following example illustrates how to read a flat file with an actual domain scenario.
+This particular batch job reads in football players from the following file:
+
+```
+ID,lastName,firstName,position,birthYear,debutYear
+"AbduKa00,Abdul-Jabbar,Karim,rb,1974,1996",
+"AbduRa00,Abdullah,Rabih,rb,1975,1999",
+"AberWa00,Abercrombie,Walter,rb,1959,1982",
+"AbraDa00,Abramowicz,Danny,wr,1945,1967",
+"AdamBo00,Adams,Bob,te,1946,1969",
+"AdamCh00,Adams,Charlie,wr,1979,2003"
+```
+
+The contents of this file are mapped to the following`Player` domain object:
+
+```
+public class Player implements Serializable {
+
+ private String ID;
+ private String lastName;
+ private String firstName;
+ private String position;
+ private int birthYear;
+ private int debutYear;
+
+ public String toString() {
+ return "PLAYER:ID=" + ID + ",Last Name=" + lastName +
+ ",First Name=" + firstName + ",Position=" + position +
+ ",Birth Year=" + birthYear + ",DebutYear=" +
+ debutYear;
+ }
+
+ // setters and getters...
+}
+```
+
+To map a `FieldSet` into a `Player` object, a `FieldSetMapper` that returns players needs
+to be defined, as shown in the following example:
+
+```
+protected static class PlayerFieldSetMapper implements FieldSetMapper {
+ public Player mapFieldSet(FieldSet fieldSet) {
+ Player player = new Player();
+
+ player.setID(fieldSet.readString(0));
+ player.setLastName(fieldSet.readString(1));
+ player.setFirstName(fieldSet.readString(2));
+ player.setPosition(fieldSet.readString(3));
+ player.setBirthYear(fieldSet.readInt(4));
+ player.setDebutYear(fieldSet.readInt(5));
+
+ return player;
+ }
+}
+```
+
+The file can then be read by correctly constructing a `FlatFileItemReader` and calling`read`, as shown in the following example:
+
+```
+FlatFileItemReader itemReader = new FlatFileItemReader<>();
+itemReader.setResource(new FileSystemResource("resources/players.csv"));
+DefaultLineMapper lineMapper = new DefaultLineMapper<>();
+//DelimitedLineTokenizer defaults to comma as its delimiter
+lineMapper.setLineTokenizer(new DelimitedLineTokenizer());
+lineMapper.setFieldSetMapper(new PlayerFieldSetMapper());
+itemReader.setLineMapper(lineMapper);
+itemReader.open(new ExecutionContext());
+Player player = itemReader.read();
+```
+
+Each call to `read` returns a new`Player` object from each line in the file. When the end of the file is
+reached, `null` is returned.
+
+##### Mapping Fields by Name
+
+There is one additional piece of functionality that is allowed by both`DelimitedLineTokenizer` and `FixedLengthTokenizer` and that is similar in function to a
+JDBC `ResultSet`. The names of the fields can be injected into either of these`LineTokenizer` implementations to increase the readability of the mapping function.
+First, the column names of all fields in the flat file are injected into the tokenizer,
+as shown in the following example:
+
+```
+tokenizer.setNames(new String[] {"ID", "lastName", "firstName", "position", "birthYear", "debutYear"});
+```
+
+A `FieldSetMapper` can use this information as follows:
+
+```
+public class PlayerMapper implements FieldSetMapper {
+ public Player mapFieldSet(FieldSet fs) {
+
+ if (fs == null) {
+ return null;
+ }
+
+ Player player = new Player();
+ player.setID(fs.readString("ID"));
+ player.setLastName(fs.readString("lastName"));
+ player.setFirstName(fs.readString("firstName"));
+ player.setPosition(fs.readString("position"));
+ player.setDebutYear(fs.readInt("debutYear"));
+ player.setBirthYear(fs.readInt("birthYear"));
+
+ return player;
+ }
+}
+```
+
+##### Automapping FieldSets to Domain Objects
+
+For many, having to write a specific `FieldSetMapper` is equally as cumbersome as writing
+a specific `RowMapper` for a `JdbcTemplate`. Spring Batch makes this easier by providing
+a `FieldSetMapper` that automatically maps fields by matching a field name with a setter
+on the object using the JavaBean specification.
+
+Again using the football example, the `BeanWrapperFieldSetMapper` configuration looks like
+the following snippet in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+```
+
+Because the `FixedLengthLineTokenizer` uses the same `LineTokenizer` interface as
+discussed earlier, it returns the same `FieldSet` as if a delimiter had been used. This
+allows the same approaches to be used in handling its output, such as using the`BeanWrapperFieldSetMapper`.
+
+| |Supporting the preceding syntax for ranges requires that a specialized property editor,`RangeArrayPropertyEditor`, be configured in the `ApplicationContext`. However, this bean
+
+
+
+
+
+
+
+
+
+```
+
+Java Configuration
+
+```
+@Bean
+public PatternMatchingCompositeLineMapper orderFileLineMapper() {
+ PatternMatchingCompositeLineMapper lineMapper =
+ new PatternMatchingCompositeLineMapper();
+
+ Map tokenizers = new HashMap<>(3);
+ tokenizers.put("USER*", userTokenizer());
+ tokenizers.put("LINEA*", lineATokenizer());
+ tokenizers.put("LINEB*", lineBTokenizer());
+
+ lineMapper.setTokenizers(tokenizers);
+
+ Map mappers = new HashMap<>(2);
+ mappers.put("USER*", userFieldSetMapper());
+ mappers.put("LINE*", lineFieldSetMapper());
+
+ lineMapper.setFieldSetMappers(mappers);
+
+ return lineMapper;
+}
+```
+
+In this example, "LINEA" and "LINEB" have separate `LineTokenizer` instances, but they both use
+the same `FieldSetMapper`.
+
+The `PatternMatchingCompositeLineMapper` uses the `PatternMatcher#match` method
+in order to select the correct delegate for each line. The `PatternMatcher` allows for
+two wildcard characters with special meaning: the question mark ("?") matches exactly one
+character, while the asterisk ("\*") matches zero or more characters. Note that, in the
+preceding configuration, all patterns end with an asterisk, making them effectively
+prefixes to lines. The `PatternMatcher` always matches the most specific pattern
+possible, regardless of the order in the configuration. So if "LINE\*" and "LINEA\*" were
+both listed as patterns, "LINEA" would match pattern "LINEA\*", while "LINEB" would match
+pattern "LINE\*". Additionally, a single asterisk ("\*") can serve as a default by matching
+any line not matched by any other pattern.
+
+The following example shows how to match a line not matched by any other pattern in XML:
+
+XML Configuration
+
+```
+ {
+
+ public String aggregate(T item);
+
+}
+```
+
+The `LineAggregator` is the logical opposite of `LineTokenizer`. `LineTokenizer` takes a`String` and returns a `FieldSet`, whereas `LineAggregator` takes an `item` and returns a`String`.
+
+###### `PassThroughLineAggregator`
+
+The most basic implementation of the `LineAggregator` interface is the`PassThroughLineAggregator`, which assumes that the object is already a string or that
+its string representation is acceptable for writing, as shown in the following code:
+
+```
+public class PassThroughLineAggregator implements LineAggregator {
+
+ public String aggregate(T item) {
+ return item.toString();
+ }
+}
+```
+
+The preceding implementation is useful if direct control of creating the string is
+required but the advantages of a `FlatFileItemWriter`, such as transaction and restart
+support, are necessary.
+
+##### Simplified File Writing Example
+
+Now that the `LineAggregator` interface and its most basic implementation,`PassThroughLineAggregator`, have been defined, the basic flow of writing can be
+explained:
+
+1. The object to be written is passed to the `LineAggregator` in order to obtain a`String`.
+
+2. The returned `String` is written to the configured file.
+
+The following excerpt from the `FlatFileItemWriter` expresses this in code:
+
+```
+public void write(T item) throws Exception {
+ write(lineAggregator.aggregate(item) + LINE_SEPARATOR);
+}
+```
+
+In XML, a simple example of configuration might look like the following:
+
+XML Configuration
+
+```
+
+
+
+
+```
+
+In Java, a simple example of configuration might look like the following:
+
+Java Configuration
+
+```
+@Bean
+public FlatFileItemWriter itemWriter() {
+ return new FlatFileItemWriterBuilder()
+ .name("itemWriter")
+ .resource(new FileSystemResource("target/test-outputs/output.txt"))
+ .lineAggregator(new PassThroughLineAggregator<>())
+ .build();
+}
+```
+
+##### `FieldExtractor`
+
+The preceding example may be useful for the most basic uses of a writing to a file.
+However, most users of the `FlatFileItemWriter` have a domain object that needs to be
+written out and, thus, must be converted into a line. In file reading, the following was
+required:
+
+1. Read one line from the file.
+
+2. Pass the line into the `LineTokenizer#tokenize()` method, in order to retrieve a`FieldSet`.
+
+3. Pass the `FieldSet` returned from tokenizing to a `FieldSetMapper`, returning the
+ result from the `ItemReader#read()` method.
+
+File writing has similar but inverse steps:
+
+1. Pass the item to be written to the writer.
+
+2. Convert the fields on the item into an array.
+
+3. Aggregate the resulting array into a line.
+
+Because there is no way for the framework to know which fields from the object need to
+be written out, a `FieldExtractor` must be written to accomplish the task of turning the
+item into an array, as shown in the following interface definition:
+
+```
+public interface FieldExtractor {
+
+ Object[] extract(T item);
+
+}
+```
+
+Implementations of the `FieldExtractor` interface should create an array from the fields
+of the provided object, which can then be written out with a delimiter between the
+elements or as part of a fixed-width line.
+
+###### `PassThroughFieldExtractor`
+
+There are many cases where a collection, such as an array, `Collection`, or `FieldSet`,
+needs to be written out. "Extracting" an array from one of these collection types is very
+straightforward. To do so, convert the collection to an array. Therefore, the`PassThroughFieldExtractor` should be used in this scenario. It should be noted that, if
+the object passed in is not a type of collection, then the `PassThroughFieldExtractor`returns an array containing solely the item to be extracted.
+
+###### `BeanWrapperFieldExtractor`
+
+As with the `BeanWrapperFieldSetMapper` described in the file reading section, it is
+often preferable to configure how to convert a domain object to an object array, rather
+than writing the conversion yourself. The `BeanWrapperFieldExtractor` provides this
+functionality, as shown in the following example:
+
+```
+BeanWrapperFieldExtractor extractor = new BeanWrapperFieldExtractor<>();
+extractor.setNames(new String[] { "first", "last", "born" });
+
+String first = "Alan";
+String last = "Turing";
+int born = 1912;
+
+Name n = new Name(first, last, born);
+Object[] values = extractor.extract(n);
+
+assertEquals(first, values[0]);
+assertEquals(last, values[1]);
+assertEquals(born, values[2]);
+```
+
+This extractor implementation has only one required property: the names of the fields to
+map. Just as the `BeanWrapperFieldSetMapper` needs field names to map fields on the`FieldSet` to setters on the provided object, the `BeanWrapperFieldExtractor` needs names
+to map to getters for creating an object array. It is worth noting that the order of the
+names determines the order of the fields within the array.
+
+##### Delimited File Writing Example
+
+The most basic flat file format is one in which all fields are separated by a delimiter.
+This can be accomplished using a `DelimitedLineAggregator`. The following example writes
+out a simple domain object that represents a credit to a customer account:
+
+```
+public class CustomerCredit {
+
+ private int id;
+ private String name;
+ private BigDecimal credit;
+
+ //getters and setters removed for clarity
+}
+```
+
+Because a domain object is being used, an implementation of the `FieldExtractor`interface must be provided, along with the delimiter to use.
+
+The following example shows how to use the `FieldExtractor` with a delimiter in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+```
+
+The following example shows how to use the `FieldExtractor` with a delimiter in Java:
+
+Java Configuration
+
+```
+@Bean
+public FlatFileItemWriter itemWriter(Resource outputResource) throws Exception {
+ BeanWrapperFieldExtractor fieldExtractor = new BeanWrapperFieldExtractor<>();
+ fieldExtractor.setNames(new String[] {"name", "credit"});
+ fieldExtractor.afterPropertiesSet();
+
+ DelimitedLineAggregator lineAggregator = new DelimitedLineAggregator<>();
+ lineAggregator.setDelimiter(",");
+ lineAggregator.setFieldExtractor(fieldExtractor);
+
+ return new FlatFileItemWriterBuilder()
+ .name("customerCreditWriter")
+ .resource(outputResource)
+ .lineAggregator(lineAggregator)
+ .build();
+}
+```
+
+In the previous example, the `BeanWrapperFieldExtractor` described earlier in this
+chapter is used to turn the name and credit fields within `CustomerCredit` into an object
+array, which is then written out with commas between each field.
+
+It is also possible to use the `FlatFileItemWriterBuilder.DelimitedBuilder` to
+automatically create the `BeanWrapperFieldExtractor` and `DelimitedLineAggregator`as shown in the following example:
+
+Java Configuration
+
+```
+@Bean
+public FlatFileItemWriter itemWriter(Resource outputResource) throws Exception {
+ return new FlatFileItemWriterBuilder()
+ .name("customerCreditWriter")
+ .resource(outputResource)
+ .delimited()
+ .delimiter("|")
+ .names(new String[] {"name", "credit"})
+ .build();
+}
+```
+
+##### Fixed Width File Writing Example
+
+Delimited is not the only type of flat file format. Many prefer to use a set width for
+each column to delineate between fields, which is usually referred to as 'fixed width'.
+Spring Batch supports this in file writing with the `FormatterLineAggregator`.
+
+Using the same `CustomerCredit` domain object described above, it can be configured as
+follows in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+```
+
+Using the same `CustomerCredit` domain object described above, it can be configured as
+follows in Java:
+
+Java Configuration
+
+```
+@Bean
+public FlatFileItemWriter itemWriter(Resource outputResource) throws Exception {
+ BeanWrapperFieldExtractor fieldExtractor = new BeanWrapperFieldExtractor<>();
+ fieldExtractor.setNames(new String[] {"name", "credit"});
+ fieldExtractor.afterPropertiesSet();
+
+ FormatterLineAggregator lineAggregator = new FormatterLineAggregator<>();
+ lineAggregator.setFormat("%-9s%-2.0f");
+ lineAggregator.setFieldExtractor(fieldExtractor);
+
+ return new FlatFileItemWriterBuilder()
+ .name("customerCreditWriter")
+ .resource(outputResource)
+ .lineAggregator(lineAggregator)
+ .build();
+}
+```
+
+Most of the preceding example should look familiar. However, the value of the format
+property is new.
+
+The following example shows the format property in XML:
+
+```
+ lineAggregator = new FormatterLineAggregator<>();
+lineAggregator.setFormat("%-9s%-2.0f");
+...
+```
+
+The underlying implementation is built using the same`Formatter` added as part of Java 5. The Java`Formatter` is based on the`printf` functionality of the C programming
+language. Most details on how to configure a formatter can be found in
+the Javadoc of [Formatter](https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html).
+
+It is also possible to use the `FlatFileItemWriterBuilder.FormattedBuilder` to
+automatically create the `BeanWrapperFieldExtractor` and `FormatterLineAggregator`as shown in following example:
+
+Java Configuration
+
+```
+@Bean
+public FlatFileItemWriter itemWriter(Resource outputResource) throws Exception {
+ return new FlatFileItemWriterBuilder()
+ .name("customerCreditWriter")
+ .resource(outputResource)
+ .formatted()
+ .format("%-9s%-2.0f")
+ .names(new String[] {"name", "credit"})
+ .build();
+}
+```
+
+##### Handling File Creation
+
+`FlatFileItemReader` has a very simple relationship with file resources. When the reader
+is initialized, it opens the file (if it exists), and throws an exception if it does not.
+File writing isn’t quite so simple. At first glance, it seems like a similar
+straightforward contract should exist for `FlatFileItemWriter`: If the file already
+exists, throw an exception, and, if it does not, create it and start writing. However,
+potentially restarting a `Job` can cause issues. In normal restart scenarios, the
+contract is reversed: If the file exists, start writing to it from the last known good
+position, and, if it does not, throw an exception. However, what happens if the file name
+for this job is always the same? In this case, you would want to delete the file if it
+exists, unless it’s a restart. Because of this possibility, the `FlatFileItemWriter`contains the property, `shouldDeleteIfExists`. Setting this property to true causes an
+existing file with the same name to be deleted when the writer is opened.
+
+### XML Item Readers and Writers
+
+Spring Batch provides transactional infrastructure for both reading XML records and
+mapping them to Java objects as well as writing Java objects as XML records.
+
+| |Constraints on streaming XML' and '\ ' is considered one 'fragment'. Spring Batch
+uses Object/XML Mapping (OXM) to bind fragments to objects. However, Spring Batch is not
+tied to any particular XML binding technology. Typical use is to delegate to[Spring OXM](https://docs.spring.io/spring/docs/current/spring-framework-reference/data-access.html#oxm), which
+provides uniform abstraction for the most popular OXM technologies. The dependency on
+Spring OXM is optional and you can choose to implement Spring Batch specific interfaces
+if desired. The relationship to the technologies that OXM supports is shown in the
+following image:
+
+
+
+Figure 2. OXM Binding
+
+With an introduction to OXM and how one can use XML fragments to represent records, we
+can now more closely examine readers and writers.
+
+#### `StaxEventItemReader`
+
+The `StaxEventItemReader` configuration provides a typical setup for the processing of
+records from an XML input stream. First, consider the following set of XML records that
+the `StaxEventItemReader` can process:
+
+```
+
+
+
+ XYZ0001
+ 5
+ 11.39
+ Customer1
+
+
+ XYZ0002
+ 2
+ 72.99
+ Customer2c
+
+
+ XYZ0003
+ 9
+ 99.99
+ Customer3
+
+
+```
+
+To be able to process the XML records, the following is needed:
+
+* Root Element Name: The name of the root element of the fragment that constitutes the
+ object to be mapped. The example configuration demonstrates this with the value of trade.
+
+* Resource: A Spring Resource that represents the file to read.
+
+* `Unmarshaller`: An unmarshalling facility provided by Spring OXM for mapping the XML
+ fragment to an object.
+
+The following example shows how to define a `StaxEventItemReader` that works with a root
+element named `trade`, a resource of `data/iosample/input/input.xml`, and an unmarshaller
+called `tradeMarshaller` in XML:
+
+XML Configuration
+
+```
+
+
+```
+
+The following example shows how to define a `StaxEventItemReader` that works with a root
+element named `trade`, a resource of `data/iosample/input/input.xml`, and an unmarshaller
+called `tradeMarshaller` in Java:
+
+Java Configuration
+
+```
+@Bean
+public StaxEventItemReader itemReader() {
+ return new StaxEventItemReaderBuilder()
+ .name("itemReader")
+ .resource(new FileSystemResource("org/springframework/batch/item/xml/domain/trades.xml"))
+ .addFragmentRootElements("trade")
+ .unmarshaller(tradeMarshaller())
+ .build();
+
+}
+```
+
+Note that, in this example, we have chosen to use an `XStreamMarshaller`, which accepts
+an alias passed in as a map with the first key and value being the name of the fragment
+(that is, a root element) and the object type to bind. Then, similar to a `FieldSet`, the
+names of the other elements that map to fields within the object type are described as
+key/value pairs in the map. In the configuration file, we can use a Spring configuration
+utility to describe the required alias.
+
+The following example shows how to describe the alias in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+```
+
+The following example shows how to describe the alias in Java:
+
+Java Configuration
+
+```
+@Bean
+public XStreamMarshaller tradeMarshaller() {
+ Map aliases = new HashMap<>();
+ aliases.put("trade", Trade.class);
+ aliases.put("price", BigDecimal.class);
+ aliases.put("isin", String.class);
+ aliases.put("customer", String.class);
+ aliases.put("quantity", Long.class);
+
+ XStreamMarshaller marshaller = new XStreamMarshaller();
+
+ marshaller.setAliases(aliases);
+
+ return marshaller;
+}
+```
+
+On input, the reader reads the XML resource until it recognizes that a new fragment is
+about to start. By default, the reader matches the element name to recognize that a new
+fragment is about to start. The reader creates a standalone XML document from the
+fragment and passes the document to a deserializer (typically a wrapper around a Spring
+OXM `Unmarshaller`) to map the XML to a Java object.
+
+In summary, this procedure is analogous to the following Java code, which uses the
+injection provided by the Spring configuration:
+
+```
+StaxEventItemReader xmlStaxEventItemReader = new StaxEventItemReader<>();
+Resource resource = new ByteArrayResource(xmlResource.getBytes());
+
+Map aliases = new HashMap();
+aliases.put("trade","org.springframework.batch.sample.domain.trade.Trade");
+aliases.put("price","java.math.BigDecimal");
+aliases.put("customer","java.lang.String");
+aliases.put("isin","java.lang.String");
+aliases.put("quantity","java.lang.Long");
+XStreamMarshaller unmarshaller = new XStreamMarshaller();
+unmarshaller.setAliases(aliases);
+xmlStaxEventItemReader.setUnmarshaller(unmarshaller);
+xmlStaxEventItemReader.setResource(resource);
+xmlStaxEventItemReader.setFragmentRootElementName("trade");
+xmlStaxEventItemReader.open(new ExecutionContext());
+
+boolean hasNext = true;
+
+Trade trade = null;
+
+while (hasNext) {
+ trade = xmlStaxEventItemReader.read();
+ if (trade == null) {
+ hasNext = false;
+ }
+ else {
+ System.out.println(trade);
+ }
+}
+```
+
+#### `StaxEventItemWriter`
+
+Output works symmetrically to input. The `StaxEventItemWriter` needs a `Resource`, a
+marshaller, and a `rootTagName`. A Java object is passed to a marshaller (typically a
+standard Spring OXM Marshaller) which writes to a `Resource` by using a custom event
+writer that filters the `StartDocument` and `EndDocument` events produced for each
+fragment by the OXM tools.
+
+The following XML example uses the `MarshallingEventWriterSerializer`:
+
+XML Configuration
+
+```
+
+
+```
+
+The following Java example uses the `MarshallingEventWriterSerializer`:
+
+Java Configuration
+
+```
+@Bean
+public StaxEventItemWriter itemWriter(Resource outputResource) {
+ return new StaxEventItemWriterBuilder()
+ .name("tradesWriter")
+ .marshaller(tradeMarshaller())
+ .resource(outputResource)
+ .rootTagName("trade")
+ .overwriteOutput(true)
+ .build();
+
+}
+```
+
+The preceding configuration sets up the three required properties and sets the optional`overwriteOutput=true` attrbute, mentioned earlier in this chapter for specifying whether
+an existing file can be overwritten.
+
+The following XML example uses the same marshaller as the one used in the reading example
+shown earlier in the chapter:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+```
+
+The following Java example uses the same marshaller as the one used in the reading example
+shown earlier in the chapter:
+
+Java Configuration
+
+```
+@Bean
+public XStreamMarshaller customerCreditMarshaller() {
+ XStreamMarshaller marshaller = new XStreamMarshaller();
+
+ Map aliases = new HashMap<>();
+ aliases.put("trade", Trade.class);
+ aliases.put("price", BigDecimal.class);
+ aliases.put("isin", String.class);
+ aliases.put("customer", String.class);
+ aliases.put("quantity", Long.class);
+
+ marshaller.setAliases(aliases);
+
+ return marshaller;
+}
+```
+
+To summarize with a Java example, the following code illustrates all of the points
+discussed, demonstrating the programmatic setup of the required properties:
+
+```
+FileSystemResource resource = new FileSystemResource("data/outputFile.xml")
+
+Map aliases = new HashMap();
+aliases.put("trade","org.springframework.batch.sample.domain.trade.Trade");
+aliases.put("price","java.math.BigDecimal");
+aliases.put("customer","java.lang.String");
+aliases.put("isin","java.lang.String");
+aliases.put("quantity","java.lang.Long");
+Marshaller marshaller = new XStreamMarshaller();
+marshaller.setAliases(aliases);
+
+StaxEventItemWriter staxItemWriter =
+ new StaxEventItemWriterBuilder()
+ .name("tradesWriter")
+ .marshaller(marshaller)
+ .resource(resource)
+ .rootTagName("trade")
+ .overwriteOutput(true)
+ .build();
+
+staxItemWriter.afterPropertiesSet();
+
+ExecutionContext executionContext = new ExecutionContext();
+staxItemWriter.open(executionContext);
+Trade trade = new Trade();
+trade.setPrice(11.39);
+trade.setIsin("XYZ0001");
+trade.setQuantity(5L);
+trade.setCustomer("Customer1");
+staxItemWriter.write(trade);
+```
+
+### JSON Item Readers And Writers
+
+Spring Batch provides support for reading and Writing JSON resources in the following format:
+
+```
+[
+ {
+ "isin": "123",
+ "quantity": 1,
+ "price": 1.2,
+ "customer": "foo"
+ },
+ {
+ "isin": "456",
+ "quantity": 2,
+ "price": 1.4,
+ "customer": "bar"
+ }
+]
+```
+
+It is assumed that the JSON resource is an array of JSON objects corresponding to
+individual items. Spring Batch is not tied to any particular JSON library.
+
+#### `JsonItemReader`
+
+The `JsonItemReader` delegates JSON parsing and binding to implementations of the`org.springframework.batch.item.json.JsonObjectReader` interface. This interface
+is intended to be implemented by using a streaming API to read JSON objects
+in chunks. Two implementations are currently provided:
+
+* [Jackson](https://github.com/FasterXML/jackson) through the `org.springframework.batch.item.json.JacksonJsonObjectReader`
+
+* [Gson](https://github.com/google/gson) through the `org.springframework.batch.item.json.GsonJsonObjectReader`
+
+To be able to process JSON records, the following is needed:
+
+* `Resource`: A Spring Resource that represents the JSON file to read.
+
+* `JsonObjectReader`: A JSON object reader to parse and bind JSON objects to items
+
+The following example shows how to define a `JsonItemReader` that works with the
+previous JSON resource `org/springframework/batch/item/json/trades.json` and a`JsonObjectReader` based on Jackson:
+
+```
+@Bean
+public JsonItemReader jsonItemReader() {
+ return new JsonItemReaderBuilder()
+ .jsonObjectReader(new JacksonJsonObjectReader<>(Trade.class))
+ .resource(new ClassPathResource("trades.json"))
+ .name("tradeJsonItemReader")
+ .build();
+}
+```
+
+#### `JsonFileItemWriter`
+
+The `JsonFileItemWriter` delegates the marshalling of items to the`org.springframework.batch.item.json.JsonObjectMarshaller` interface. The contract
+of this interface is to take an object and marshall it to a JSON `String`.
+Two implementations are currently provided:
+
+* [Jackson](https://github.com/FasterXML/jackson) through the `org.springframework.batch.item.json.JacksonJsonObjectMarshaller`
+
+* [Gson](https://github.com/google/gson) through the `org.springframework.batch.item.json.GsonJsonObjectMarshaller`
+
+To be able to write JSON records, the following is needed:
+
+* `Resource`: A Spring `Resource` that represents the JSON file to write
+
+* `JsonObjectMarshaller`: A JSON object marshaller to marshall objects to JSON format
+
+The following example shows how to define a `JsonFileItemWriter`:
+
+```
+@Bean
+public JsonFileItemWriter jsonFileItemWriter() {
+ return new JsonFileItemWriterBuilder()
+ .jsonObjectMarshaller(new JacksonJsonObjectMarshaller<>())
+ .resource(new ClassPathResource("trades.json"))
+ .name("tradeJsonFileItemWriter")
+ .build();
+}
+```
+
+### Multi-File Input
+
+It is a common requirement to process multiple files within a single `Step`. Assuming the
+files all have the same formatting, the `MultiResourceItemReader` supports this type of
+input for both XML and flat file processing. Consider the following files in a directory:
+
+```
+file-1.txt file-2.txt ignored.txt
+```
+
+file-1.txt and file-2.txt are formatted the same and, for business reasons, should be
+processed together. The `MultiResourceItemReader` can be used to read in both files by
+using wildcards.
+
+The following example shows how to read files with wildcards in XML:
+
+XML Configuration
+
+```
+
+
+```
+
+The following example shows how to read files with wildcards in Java:
+
+Java Configuration
+
+```
+@Bean
+public MultiResourceItemReader multiResourceReader() {
+ return new MultiResourceItemReaderBuilder()
+ .delegate(flatFileItemReader())
+ .resources(resources())
+ .build();
+}
+```
+
+The referenced delegate is a simple `FlatFileItemReader`. The above configuration reads
+input from both files, handling rollback and restart scenarios. It should be noted that,
+as with any `ItemReader`, adding extra input (in this case a file) could cause potential
+issues when restarting. It is recommended that batch jobs work with their own individual
+directories until completed successfully.
+
+| |Input resources are ordered by using `MultiResourceItemReader#setComparator(Comparator)`to make sure resource ordering is preserved between job runs in restart scenario.|
+|---|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+
+### Database
+
+Like most enterprise application styles, a database is the central storage mechanism for
+batch. However, batch differs from other application styles due to the sheer size of the
+datasets with which the system must work. If a SQL statement returns 1 million rows, the
+result set probably holds all returned results in memory until all rows have been read.
+Spring Batch provides two types of solutions for this problem:
+
+* [Cursor-based `ItemReader` Implementations](#cursorBasedItemReaders)
+
+* [Paging `ItemReader` Implementations](#pagingItemReaders)
+
+#### Cursor-based `ItemReader` Implementations
+
+Using a database cursor is generally the default approach of most batch developers,
+because it is the database’s solution to the problem of 'streaming' relational data. The
+Java `ResultSet` class is essentially an object oriented mechanism for manipulating a
+cursor. A `ResultSet` maintains a cursor to the current row of data. Calling `next` on a`ResultSet` moves this cursor to the next row. The Spring Batch cursor-based `ItemReader`implementation opens a cursor on initialization and moves the cursor forward one row for
+every call to `read`, returning a mapped object that can be used for processing. The`close` method is then called to ensure all resources are freed up. The Spring core`JdbcTemplate` gets around this problem by using the callback pattern to completely map
+all rows in a `ResultSet` and close before returning control back to the method caller.
+However, in batch, this must wait until the step is complete. The following image shows a
+generic diagram of how a cursor-based `ItemReader` works. Note that, while the example
+uses SQL (because SQL is so widely known), any technology could implement the basic
+approach.
+
+
+
+Figure 3. Cursor Example
+
+This example illustrates the basic pattern. Given a 'FOO' table, which has three columns:`ID`, `NAME`, and `BAR`, select all rows with an ID greater than 1 but less than 7. This
+puts the beginning of the cursor (row 1) on ID 2. The result of this row should be a
+completely mapped `Foo` object. Calling `read()` again moves the cursor to the next row,
+which is the `Foo` with an ID of 3. The results of these reads are written out after each`read`, allowing the objects to be garbage collected (assuming no instance variables are
+maintaining references to them).
+
+##### `JdbcCursorItemReader`
+
+`JdbcCursorItemReader` is the JDBC implementation of the cursor-based technique. It works
+directly with a `ResultSet` and requires an SQL statement to run against a connection
+obtained from a `DataSource`. The following database schema is used as an example:
+
+```
+CREATE TABLE CUSTOMER (
+ ID BIGINT IDENTITY PRIMARY KEY,
+ NAME VARCHAR(45),
+ CREDIT FLOAT
+);
+```
+
+Many people prefer to use a domain object for each row, so the following example uses an
+implementation of the `RowMapper` interface to map a `CustomerCredit` object:
+
+```
+public class CustomerCreditRowMapper implements RowMapper {
+
+ public static final String ID_COLUMN = "id";
+ public static final String NAME_COLUMN = "name";
+ public static final String CREDIT_COLUMN = "credit";
+
+ public CustomerCredit mapRow(ResultSet rs, int rowNum) throws SQLException {
+ CustomerCredit customerCredit = new CustomerCredit();
+
+ customerCredit.setId(rs.getInt(ID_COLUMN));
+ customerCredit.setName(rs.getString(NAME_COLUMN));
+ customerCredit.setCredit(rs.getBigDecimal(CREDIT_COLUMN));
+
+ return customerCredit;
+ }
+}
+```
+
+Because `JdbcCursorItemReader` shares key interfaces with `JdbcTemplate`, it is useful to
+see an example of how to read in this data with `JdbcTemplate`, in order to contrast it
+with the `ItemReader`. For the purposes of this example, assume there are 1,000 rows in
+the `CUSTOMER` database. The first example uses `JdbcTemplate`:
+
+```
+//For simplicity sake, assume a dataSource has already been obtained
+JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
+List customerCredits = jdbcTemplate.query("SELECT ID, NAME, CREDIT from CUSTOMER",
+ new CustomerCreditRowMapper());
+```
+
+After running the preceding code snippet, the `customerCredits` list contains 1,000`CustomerCredit` objects. In the query method, a connection is obtained from the`DataSource`, the provided SQL is run against it, and the `mapRow` method is called for
+each row in the `ResultSet`. Contrast this with the approach of the`JdbcCursorItemReader`, shown in the following example:
+
+```
+JdbcCursorItemReader itemReader = new JdbcCursorItemReader();
+itemReader.setDataSource(dataSource);
+itemReader.setSql("SELECT ID, NAME, CREDIT from CUSTOMER");
+itemReader.setRowMapper(new CustomerCreditRowMapper());
+int counter = 0;
+ExecutionContext executionContext = new ExecutionContext();
+itemReader.open(executionContext);
+Object customerCredit = new Object();
+while(customerCredit != null){
+ customerCredit = itemReader.read();
+ counter++;
+}
+itemReader.close();
+```
+
+After running the preceding code snippet, the counter equals 1,000. If the code above had
+put the returned `customerCredit` into a list, the result would have been exactly the
+same as with the `JdbcTemplate` example. However, the big advantage of the `ItemReader`is that it allows items to be 'streamed'. The `read` method can be called once, the item
+can be written out by an `ItemWriter`, and then the next item can be obtained with`read`. This allows item reading and writing to be done in 'chunks' and committed
+periodically, which is the essence of high performance batch processing. Furthermore, it
+is easily configured for injection into a Spring Batch `Step`.
+
+The following example shows how to inject an `ItemReader` into a `Step` in XML:
+
+XML Configuration
+
+```
+
+
+
+
+```
+
+The following example shows how to inject an `ItemReader` into a `Step` in Java:
+
+Java Configuration
+
+```
+@Bean
+public JdbcCursorItemReader itemReader() {
+ return new JdbcCursorItemReaderBuilder()
+ .dataSource(this.dataSource)
+ .name("creditReader")
+ .sql("select ID, NAME, CREDIT from CUSTOMER")
+ .rowMapper(new CustomerCreditRowMapper())
+ .build();
+
+}
+```
+
+###### Additional Properties
+
+Because there are so many varying options for opening a cursor in Java, there are many
+properties on the `JdbcCursorItemReader` that can be set, as described in the following
+table:
+
+| ignoreWarnings | Determines whether or not SQLWarnings are logged or cause an exception.
+
+```
+
+The following example shows how to inject a Hibernate `ItemReader` in Java:
+
+Java Configuration
+
+```
+@Bean
+public HibernateCursorItemReader itemReader(SessionFactory sessionFactory) {
+ return new HibernateCursorItemReaderBuilder()
+ .name("creditReader")
+ .sessionFactory(sessionFactory)
+ .queryString("from CustomerCredit")
+ .build();
+}
+```
+
+##### `StoredProcedureItemReader`
+
+Sometimes it is necessary to obtain the cursor data by using a stored procedure. The`StoredProcedureItemReader` works like the `JdbcCursorItemReader`, except that, instead
+of running a query to obtain a cursor, it runs a stored procedure that returns a cursor.
+The stored procedure can return the cursor in three different ways:
+
+* As a returned `ResultSet` (used by SQL Server, Sybase, DB2, Derby, and MySQL).
+
+* As a ref-cursor returned as an out parameter (used by Oracle and PostgreSQL).
+
+* As the return value of a stored function call.
+
+The following XML example configuration uses the same 'customer credit' example as earlier
+examples:
+
+XML Configuration
+
+```
+
+
+
+
+```
+
+The following Java example configuration uses the same 'customer credit' example as
+earlier examples:
+
+Java Configuration
+
+```
+@Bean
+public StoredProcedureItemReader reader(DataSource dataSource) {
+ StoredProcedureItemReader reader = new StoredProcedureItemReader();
+
+ reader.setDataSource(dataSource);
+ reader.setProcedureName("sp_customer_credit");
+ reader.setRowMapper(new CustomerCreditRowMapper());
+
+ return reader;
+}
+```
+
+The preceding example relies on the stored procedure to provide a `ResultSet` as a
+returned result (option 1 from earlier).
+
+If the stored procedure returned a `ref-cursor` (option 2), then we would need to provide
+the position of the out parameter that is the returned `ref-cursor`.
+
+The following example shows how to work with the first parameter being a ref-cursor in
+XML:
+
+XML Configuration
+
+```
+
+
+
+
+```
+
+The following example shows how to work with the first parameter being a ref-cursor in
+Java:
+
+Java Configuration
+
+```
+@Bean
+public StoredProcedureItemReader reader(DataSource dataSource) {
+ StoredProcedureItemReader reader = new StoredProcedureItemReader();
+
+ reader.setDataSource(dataSource);
+ reader.setProcedureName("sp_customer_credit");
+ reader.setRowMapper(new CustomerCreditRowMapper());
+ reader.setRefCursorPosition(1);
+
+ return reader;
+}
+```
+
+If the cursor was returned from a stored function (option 3), we would need to set the
+property "function" to `true`. It defaults to `false`.
+
+The following example shows property to `true` in XML:
+
+XML Configuration
+
+```
+
+
+
+
+```
+
+The following example shows property to `true` in Java:
+
+Java Configuration
+
+```
+@Bean
+public StoredProcedureItemReader reader(DataSource dataSource) {
+ StoredProcedureItemReader reader = new StoredProcedureItemReader();
+
+ reader.setDataSource(dataSource);
+ reader.setProcedureName("sp_customer_credit");
+ reader.setRowMapper(new CustomerCreditRowMapper());
+ reader.setFunction(true);
+
+ return reader;
+}
+```
+
+In all of these cases, we need to define a `RowMapper` as well as a `DataSource` and the
+actual procedure name.
+
+If the stored procedure or function takes in parameters, then they must be declared and
+set by using the `parameters` property. The following example, for Oracle, declares three
+parameters. The first one is the `out` parameter that returns the ref-cursor, and the
+second and third are in parameters that takes a value of type `INTEGER`.
+
+The following example shows how to work with parameters in XML:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+```
+
+The following example shows how to work with parameters in Java:
+
+Java Configuration
+
+```
+@Bean
+public StoredProcedureItemReader reader(DataSource dataSource) {
+ List parameters = new ArrayList<>();
+ parameters.add(new SqlOutParameter("newId", OracleTypes.CURSOR));
+ parameters.add(new SqlParameter("amount", Types.INTEGER);
+ parameters.add(new SqlParameter("custId", Types.INTEGER);
+
+ StoredProcedureItemReader reader = new StoredProcedureItemReader();
+
+ reader.setDataSource(dataSource);
+ reader.setProcedureName("spring.cursor_func");
+ reader.setParameters(parameters);
+ reader.setRefCursorPosition(1);
+ reader.setRowMapper(rowMapper());
+ reader.setPreparedStatementSetter(parameterSetter());
+
+ return reader;
+}
+```
+
+In addition to the parameter declarations, we need to specify a `PreparedStatementSetter`implementation that sets the parameter values for the call. This works the same as for
+the `JdbcCursorItemReader` above. All the additional properties listed in[Additional Properties](#JdbcCursorItemReaderProperties) apply to the `StoredProcedureItemReader` as well.
+
+#### Paging `ItemReader` Implementations
+
+An alternative to using a database cursor is running multiple queries where each query
+fetches a portion of the results. We refer to this portion as a page. Each query must
+specify the starting row number and the number of rows that we want returned in the page.
+
+##### `JdbcPagingItemReader`
+
+One implementation of a paging `ItemReader` is the `JdbcPagingItemReader`. The`JdbcPagingItemReader` needs a `PagingQueryProvider` responsible for providing the SQL
+queries used to retrieve the rows making up a page. Since each database has its own
+strategy for providing paging support, we need to use a different `PagingQueryProvider`for each supported database type. There is also the `SqlPagingQueryProviderFactoryBean`that auto-detects the database that is being used and determine the appropriate`PagingQueryProvider` implementation. This simplifies the configuration and is the
+recommended best practice.
+
+The `SqlPagingQueryProviderFactoryBean` requires that you specify a `select` clause and a`from` clause. You can also provide an optional `where` clause. These clauses and the
+required `sortKey` are used to build an SQL statement.
+
+| |It is important to have a unique key constraint on the `sortKey` to guarantee that
+
+
+
+
+
+
+
+
+
+```
+
+The following Java example configuration uses a similar 'customer credit' example as the
+cursor-based `ItemReaders` shown previously:
+
+Java Configuration
+
+```
+@Bean
+public JdbcPagingItemReader itemReader(DataSource dataSource, PagingQueryProvider queryProvider) {
+ Map parameterValues = new HashMap<>();
+ parameterValues.put("status", "NEW");
+
+ return new JdbcPagingItemReaderBuilder()
+ .name("creditReader")
+ .dataSource(dataSource)
+ .queryProvider(queryProvider)
+ .parameterValues(parameterValues)
+ .rowMapper(customerCreditMapper())
+ .pageSize(1000)
+ .build();
+}
+
+@Bean
+public SqlPagingQueryProviderFactoryBean queryProvider() {
+ SqlPagingQueryProviderFactoryBean provider = new SqlPagingQueryProviderFactoryBean();
+
+ provider.setSelectClause("select id, name, credit");
+ provider.setFromClause("from customer");
+ provider.setWhereClause("where status=:status");
+ provider.setSortKey("id");
+
+ return provider;
+}
+```
+
+This configured `ItemReader` returns `CustomerCredit` objects using the `RowMapper`,
+which must be specified. The 'pageSize' property determines the number of entities read
+from the database for each query run.
+
+The 'parameterValues' property can be used to specify a `Map` of parameter values for the
+query. If you use named parameters in the `where` clause, the key for each entry should
+match the name of the named parameter. If you use a traditional '?' placeholder, then the
+key for each entry should be the number of the placeholder, starting with 1.
+
+##### `JpaPagingItemReader`
+
+Another implementation of a paging `ItemReader` is the `JpaPagingItemReader`. JPA does
+not have a concept similar to the Hibernate `StatelessSession`, so we have to use other
+features provided by the JPA specification. Since JPA supports paging, this is a natural
+choice when it comes to using JPA for batch processing. After each page is read, the
+entities become detached and the persistence context is cleared, to allow the entities to
+be garbage collected once the page is processed.
+
+The `JpaPagingItemReader` lets you declare a JPQL statement and pass in a`EntityManagerFactory`. It then passes back one item per call to read in the same basic
+fashion as any other `ItemReader`. The paging happens behind the scenes when additional
+entities are needed.
+
+The following XML example configuration uses the same 'customer credit' example as the
+JDBC reader shown previously:
+
+XML Configuration
+
+```
+
+
+```
+
+The following Java example configuration uses the same 'customer credit' example as the
+JDBC reader shown previously:
+
+Java Configuration
+
+```
+@Bean
+public JpaPagingItemReader itemReader() {
+ return new JpaPagingItemReaderBuilder()
+ .name("creditReader")
+ .entityManagerFactory(entityManagerFactory())
+ .queryString("select c from CustomerCredit c")
+ .pageSize(1000)
+ .build();
+}
+```
+
+This configured `ItemReader` returns `CustomerCredit` objects in the exact same manner as
+described for the `JdbcPagingItemReader` above, assuming the `CustomerCredit` object has the
+correct JPA annotations or ORM mapping file. The 'pageSize' property determines the
+number of entities read from the database for each query execution.
+
+#### Database ItemWriters
+
+While both flat files and XML files have a specific `ItemWriter` instance, there is no exact equivalent
+in the database world. This is because transactions provide all the needed functionality.`ItemWriter` implementations are necessary for files because they must act as if they’re transactional,
+keeping track of written items and flushing or clearing at the appropriate times.
+Databases have no need for this functionality, since the write is already contained in a
+transaction. Users can create their own DAOs that implement the `ItemWriter` interface or
+use one from a custom `ItemWriter` that’s written for generic processing concerns. Either
+way, they should work without any issues. One thing to look out for is the performance
+and error handling capabilities that are provided by batching the outputs. This is most
+common when using hibernate as an `ItemWriter` but could have the same issues when using
+JDBC batch mode. Batching database output does not have any inherent flaws, assuming we
+are careful to flush and there are no errors in the data. However, any errors while
+writing can cause confusion, because there is no way to know which individual item caused
+an exception or even if any individual item was responsible, as illustrated in the
+following image:
+
+
+
+Figure 4. Error On Flush
+
+If items are buffered before being written, any errors are not thrown until the buffer is
+flushed just before a commit. For example, assume that 20 items are written per chunk,
+and the 15th item throws a `DataIntegrityViolationException`. As far as the `Step`is concerned, all 20 item are written successfully, since there is no way to know that an
+error occurs until they are actually written. Once `Session#flush()` is called, the
+buffer is emptied and the exception is hit. At this point, there is nothing the `Step`can do. The transaction must be rolled back. Normally, this exception might cause the
+item to be skipped (depending upon the skip/retry policies), and then it is not written
+again. However, in the batched scenario, there is no way to know which item caused the
+issue. The whole buffer was being written when the failure happened. The only way to
+solve this issue is to flush after each item, as shown in the following image:
+
+
+
+Figure 5. Error On Write
+
+This is a common use case, especially when using Hibernate, and the simple guideline for
+implementations of `ItemWriter` is to flush on each call to `write()`. Doing so allows
+for items to be skipped reliably, with Spring Batch internally taking care of the
+granularity of the calls to `ItemWriter` after an error.
+
+### Reusing Existing Services
+
+Batch systems are often used in conjunction with other application styles. The most
+common is an online system, but it may also support integration or even a thick client
+application by moving necessary bulk data that each application style uses. For this
+reason, it is common that many users want to reuse existing DAOs or other services within
+their batch jobs. The Spring container itself makes this fairly easy by allowing any
+necessary class to be injected. However, there may be cases where the existing service
+needs to act as an `ItemReader` or `ItemWriter`, either to satisfy the dependency of
+another Spring Batch class or because it truly is the main `ItemReader` for a step. It is
+fairly trivial to write an adapter class for each service that needs wrapping, but
+because it is such a common concern, Spring Batch provides implementations:`ItemReaderAdapter` and `ItemWriterAdapter`. Both classes implement the standard Spring
+method by invoking the delegate pattern and are fairly simple to set up.
+
+The following XML example uses the `ItemReaderAdapter`:
+
+XML Configuration
+
+```
+
+
+
+
+
+
+
+
+
+
+
+ SELECT games.player_id, games.year_no, SUM(COMPLETES),
+ SUM(ATTEMPTS), SUM(PASSING_YARDS), SUM(PASSING_TD),
+ SUM(INTERCEPTIONS), SUM(RUSHES), SUM(RUSH_YARDS),
+ SUM(RECEPTIONS), SUM(RECEPTIONS_YARDS), SUM(TOTAL_TD)
+ from games, players where players.player_id =
+ games.player_id group by games.player_id, games.year_no
+
+
+
+```
+
+The following bean definition shows how to prevent state persistence in Java:
+
+Java Configuration
+
+```
+@Bean
+public JdbcCursorItemReader playerSummarizationSource(DataSource dataSource) {
+ return new JdbcCursorItemReaderBuilder()
+ .dataSource(dataSource)
+ .rowMapper(new PlayerSummaryMapper())
+ .saveState(false)
+ .sql("SELECT games.player_id, games.year_no, SUM(COMPLETES),"
+ + "SUM(ATTEMPTS), SUM(PASSING_YARDS), SUM(PASSING_TD),"
+ + "SUM(INTERCEPTIONS), SUM(RUSHES), SUM(RUSH_YARDS),"
+ + "SUM(RECEPTIONS), SUM(RECEPTIONS_YARDS), SUM(TOTAL_TD)"
+ + "from games, players where players.player_id ="
+ + "games.player_id group by games.player_id, games.year_no")
+ .build();
+
+}
+```
+
+The `ItemReader` configured above does not make any entries in the `ExecutionContext` for
+any executions in which it participates.
+
+### Creating Custom ItemReaders and ItemWriters
+
+So far, this chapter has discussed the basic contracts of reading and writing in Spring
+Batch and some common implementations for doing so. However, these are all fairly
+generic, and there are many potential scenarios that may not be covered by out-of-the-box
+implementations. This section shows, by using a simple example, how to create a custom`ItemReader` and `ItemWriter` implementation and implement their contracts correctly. The`ItemReader` also implements `ItemStream`, in order to illustrate how to make a reader or
+writer restartable.
+
+#### Custom `ItemReader` Example
+
+For the purpose of this example, we create a simple `ItemReader` implementation that
+reads from a provided list. We start by implementing the most basic contract of`ItemReader`, the `read` method, as shown in the following code:
+
+```
+public class CustomItemReader implements ItemReader {
+
+ List items;
+
+ public CustomItemReader(List items) {
+ this.items = items;
+ }
+
+ public T read() throws Exception, UnexpectedInputException,
+ NonTransientResourceException, ParseException {
+
+ if (!items.isEmpty()) {
+ return items.remove(0);
+ }
+ return null;
+ }
+}
+```
+
+The preceding class takes a list of items and returns them one at a time, removing each
+from the list. When the list is empty, it returns `null`, thus satisfying the most basic
+requirements of an `ItemReader`, as illustrated in the following test code:
+
+```
+List items = new ArrayList<>();
+items.add("1");
+items.add("2");
+items.add("3");
+
+ItemReader itemReader = new CustomItemReader<>(items);
+assertEquals("1", itemReader.read());
+assertEquals("2", itemReader.read());
+assertEquals("3", itemReader.read());
+assertNull(itemReader.read());
+```
+
+##### Making the `ItemReader` Restartable
+
+The final challenge is to make the `ItemReader` restartable. Currently, if processing is
+interrupted and begins again, the `ItemReader` must start at the beginning. This is
+actually valid in many scenarios, but it is sometimes preferable that a batch job
+restarts where it left off. The key discriminant is often whether the reader is stateful
+or stateless. A stateless reader does not need to worry about restartability, but a
+stateful one has to try to reconstitute its last known state on restart. For this reason,
+we recommend that you keep custom readers stateless if possible, so you need not worry
+about restartability.
+
+If you do need to store state, then the `ItemStream` interface should be used:
+
+```
+public class CustomItemReader implements ItemReader, ItemStream {
+
+ List items;
+ int currentIndex = 0;
+ private static final String CURRENT_INDEX = "current.index";
+
+ public CustomItemReader(List items) {
+ this.items = items;
+ }
+
+ public T read() throws Exception, UnexpectedInputException,
+ ParseException, NonTransientResourceException {
+
+ if (currentIndex < items.size()) {
+ return items.get(currentIndex++);
+ }
+
+ return null;
+ }
+
+ public void open(ExecutionContext executionContext) throws ItemStreamException {
+ if (executionContext.containsKey(CURRENT_INDEX)) {
+ currentIndex = new Long(executionContext.getLong(CURRENT_INDEX)).intValue();
+ }
+ else {
+ currentIndex = 0;
+ }
+ }
+
+ public void update(ExecutionContext executionContext) throws ItemStreamException {
+ executionContext.putLong(CURRENT_INDEX, new Long(currentIndex).longValue());
+ }
+
+ public void close() throws ItemStreamException {}
+}
+```
+
+On each call to the `ItemStream` `update` method, the current index of the `ItemReader`is stored in the provided `ExecutionContext` with a key of 'current.index'. When the`ItemStream` `open` method is called, the `ExecutionContext` is checked to see if it
+contains an entry with that key. If the key is found, then the current index is moved to
+that location. This is a fairly trivial example, but it still meets the general contract:
+
+```
+ExecutionContext executionContext = new ExecutionContext();
+((ItemStream)itemReader).open(executionContext);
+assertEquals("1", itemReader.read());
+((ItemStream)itemReader).update(executionContext);
+
+List items = new ArrayList<>();
+items.add("1");
+items.add("2");
+items.add("3");
+itemReader = new CustomItemReader<>(items);
+
+((ItemStream)itemReader).open(executionContext);
+assertEquals("2", itemReader.read());
+```
+
+Most `ItemReaders` have much more sophisticated restart logic. The`JdbcCursorItemReader`, for example, stores the row ID of the last processed row in the
+cursor.
+
+It is also worth noting that the key used within the `ExecutionContext` should not be
+trivial. That is because the same `ExecutionContext` is used for all `ItemStreams` within
+a `Step`. In most cases, simply prepending the key with the class name should be enough
+to guarantee uniqueness. However, in the rare cases where two of the same type of`ItemStream` are used in the same step (which can happen if two files are needed for
+output), a more unique name is needed. For this reason, many of the Spring Batch`ItemReader` and `ItemWriter` implementations have a `setName()` property that lets this
+key name be overridden.
+
+#### Custom `ItemWriter` Example
+
+Implementing a Custom `ItemWriter` is similar in many ways to the `ItemReader` example
+above but differs in enough ways as to warrant its own example. However, adding
+restartability is essentially the same, so it is not covered in this example. As with the`ItemReader` example, a `List` is used in order to keep the example as simple as
+possible:
+
+```
+public class CustomItemWriter implements ItemWriter {
+
+ List output = TransactionAwareProxyFactory.createTransactionalList();
+
+ public void write(List items) throws Exception {
+ output.addAll(items);
+ }
+
+ public List getOutput() {
+ return output;
+ }
+}
+```
+
+##### Making the `ItemWriter` Restartable
+
+To make the `ItemWriter` restartable, we would follow the same process as for the`ItemReader`, adding and implementing the `ItemStream` interface to synchronize the
+execution context. In the example, we might have to count the number of items processed
+and add that as a footer record. If we needed to do that, we could implement`ItemStream` in our `ItemWriter` so that the counter was reconstituted from the execution
+context if the stream was re-opened.
+
+In many realistic cases, custom `ItemWriters` also delegate to another writer that itself
+is restartable (for example, when writing to a file), or else it writes to a
+transactional resource and so does not need to be restartable, because it is stateless.
+When you have a stateful writer you should probably be sure to implement `ItemStream` as
+well as `ItemWriter`. Remember also that the client of the writer needs to be aware of
+the `ItemStream`, so you may need to register it as a stream in the configuration.
+
+### Item Reader and Writer Implementations
+
+In this section, we will introduce you to readers and writers that have not already been
+discussed in the previous sections.
+
+#### Decorators
+
+In some cases, a user needs specialized behavior to be appended to a pre-existing`ItemReader`. Spring Batch offers some out of the box decorators that can add
+additional behavior to to your `ItemReader` and `ItemWriter` implementations.
+
+Spring Batch includes the following decorators:
+
+* [`SynchronizedItemStreamReader`](#synchronizedItemStreamReader)
+
+* [`SingleItemPeekableItemReader`](#singleItemPeekableItemReader)
+
+* [`SynchronizedItemStreamWriter`](#synchronizedItemStreamWriter)
+
+* [`MultiResourceItemWriter`](#multiResourceItemWriter)
+
+* [`ClassifierCompositeItemWriter`](#classifierCompositeItemWriter)
+
+* [`ClassifierCompositeItemProcessor`](#classifierCompositeItemProcessor)
+
+##### `SynchronizedItemStreamReader`
+
+When using an `ItemReader` that is not thread safe, Spring Batch offers the`SynchronizedItemStreamReader` decorator, which can be used to make the `ItemReader`thread safe. Spring Batch provides a `SynchronizedItemStreamReaderBuilder` to construct
+an instance of the `SynchronizedItemStreamReader`.
+
+##### `SingleItemPeekableItemReader`
+
+Spring Batch includes a decorator that adds a peek method to an `ItemReader`. This peek
+method lets the user peek one item ahead. Repeated calls to the peek returns the same
+item, and this is the next item returned from the `read` method. Spring Batch provides a`SingleItemPeekableItemReaderBuilder` to construct an instance of the`SingleItemPeekableItemReader`.
+
+| |SingleItemPeekableItemReader’s peek method is not thread-safe, because it would not
+
+
+ T execute(RetryCallback retryCallback) throws E;
+
+ T execute(RetryCallback retryCallback, RecoveryCallback recoveryCallback)
+ throws E;
+
+ T execute(RetryCallback retryCallback, RetryState retryState)
+ throws E, ExhaustedRetryException;
+
+ T execute(RetryCallback retryCallback, RecoveryCallback recoveryCallback,
+ RetryState retryState) throws E;
+
+}
+```
+
+The basic callback is a simple interface that lets you insert some business logic to be
+retried, as shown in the following interface definition:
+
+```
+public interface RetryCallback {
+
+ T doWithRetry(RetryContext context) throws E;
+
+}
+```
+
+The callback runs and, if it fails (by throwing an `Exception`), it is retried until
+either it is successful or the implementation aborts. There are a number of overloaded`execute` methods in the `RetryOperations` interface. Those methods deal with various use
+cases for recovery when all retry attempts are exhausted and deal with retry state, which
+lets clients and implementations store information between calls (we cover this in more
+detail later in the chapter).
+
+The simplest general purpose implementation of `RetryOperations` is `RetryTemplate`. It
+can be used as follows:
+
+```
+RetryTemplate template = new RetryTemplate();
+
+TimeoutRetryPolicy policy = new TimeoutRetryPolicy();
+policy.setTimeout(30000L);
+
+template.setRetryPolicy(policy);
+
+Foo result = template.execute(new RetryCallback() {
+
+ public Foo doWithRetry(RetryContext context) {
+ // Do stuff that might fail, e.g. webservice operation
+ return result;
+ }
+
+});
+```
+
+In the preceding example, we make a web service call and return the result to the user. If
+that call fails, then it is retried until a timeout is reached.
+
+#### `RetryContext`
+
+The method parameter for the `RetryCallback` is a `RetryContext`. Many callbacks ignore
+the context, but, if necessary, it can be used as an attribute bag to store data for the
+duration of the iteration.
+
+A `RetryContext` has a parent context if there is a nested retry in progress in the same
+thread. The parent context is occasionally useful for storing data that need to be shared
+between calls to `execute`.
+
+#### `RecoveryCallback`
+
+When a retry is exhausted, the `RetryOperations` can pass control to a different callback,
+called the `RecoveryCallback`. To use this feature, clients pass in the callbacks together
+to the same method, as shown in the following example:
+
+```
+Foo foo = template.execute(new RetryCallback() {
+ public Foo doWithRetry(RetryContext context) {
+ // business logic here
+ },
+ new RecoveryCallback() {
+ Foo recover(RetryContext context) throws Exception {
+ // recover logic here
+ }
+});
+```
+
+If the business logic does not succeed before the template decides to abort, then the
+client is given the chance to do some alternate processing through the recovery callback.
+
+#### Stateless Retry
+
+In the simplest case, a retry is just a while loop. The `RetryTemplate` can just keep
+trying until it either succeeds or fails. The `RetryContext` contains some state to
+determine whether to retry or abort, but this state is on the stack and there is no need
+to store it anywhere globally, so we call this stateless retry. The distinction between
+stateless and stateful retry is contained in the implementation of the `RetryPolicy` (the`RetryTemplate` can handle both). In a stateless retry, the retry callback is always
+executed in the same thread it was on when it failed.
+
+#### Stateful Retry
+
+Where the failure has caused a transactional resource to become invalid, there are some
+special considerations. This does not apply to a simple remote call because there is no
+transactional resource (usually), but it does sometimes apply to a database update,
+especially when using Hibernate. In this case it only makes sense to re-throw the
+exception that called the failure immediately, so that the transaction can roll back and
+we can start a new, valid transaction.
+
+In cases involving transactions, a stateless retry is not good enough, because the
+re-throw and roll back necessarily involve leaving the `RetryOperations.execute()` method
+and potentially losing the context that was on the stack. To avoid losing it we have to
+introduce a storage strategy to lift it off the stack and put it (at a minimum) in heap
+storage. For this purpose, Spring Batch provides a storage strategy called`RetryContextCache`, which can be injected into the `RetryTemplate`. The default
+implementation of the `RetryContextCache` is in memory, using a simple `Map`. Advanced
+usage with multiple processes in a clustered environment might also consider implementing
+the `RetryContextCache` with a cluster cache of some sort (however, even in a clustered
+environment, this might be overkill).
+
+Part of the responsibility of the `RetryOperations` is to recognize the failed operations
+when they come back in a new execution (and usually wrapped in a new transaction). To
+facilitate this, Spring Batch provides the `RetryState` abstraction. This works in
+conjunction with a special `execute` methods in the `RetryOperations` interface.
+
+The way the failed operations are recognized is by identifying the state across multiple
+invocations of the retry. To identify the state, the user can provide a `RetryState`object that is responsible for returning a unique key identifying the item. The identifier
+is used as a key in the `RetryContextCache` interface.
+
+| |Be very careful with the implementation of `Object.equals()` and `Object.hashCode()` in() {
+ public Foo doWithRetry(RetryContext context) {
+ // business logic here
+ }
+});
+```
+
+There is also a more flexible implementation called `ExceptionClassifierRetryPolicy`,
+which lets the user configure different retry behavior for an arbitrary set of exception
+types though the `ExceptionClassifier` abstraction. The policy works by calling on the
+classifier to convert an exception into a delegate `RetryPolicy`. For example, one
+exception type can be retried more times before failure than another by mapping it to a
+different policy.
+
+Users might need to implement their own retry policies for more customized decisions. For
+instance, a custom retry policy makes sense when there is a well-known, solution-specific
+classification of exceptions into retryable and not retryable.
+
+### Backoff Policies
+
+When retrying after a transient failure, it often helps to wait a bit before trying again,
+because usually the failure is caused by some problem that can only be resolved by
+waiting. If a `RetryCallback` fails, the `RetryTemplate` can pause execution according to
+the `BackoffPolicy`.
+
+The following code shows the interface definition for the `BackOffPolicy` interface:
+
+```
+public interface BackoffPolicy {
+
+ BackOffContext start(RetryContext context);
+
+ void backOff(BackOffContext backOffContext)
+ throws BackOffInterruptedException;
+
+}
+```
+
+A `BackoffPolicy` is free to implement the backOff in any way it chooses. The policies
+provided by Spring Batch out of the box all use `Object.wait()`. A common use case is to
+backoff with an exponentially increasing wait period, to avoid two retries getting into
+lock step and both failing (this is a lesson learned from ethernet). For this purpose,
+Spring Batch provides the `ExponentialBackoffPolicy`.
+
+### Listeners
+
+Often, it is useful to be able to receive additional callbacks for cross cutting concerns
+across a number of different retries. For this purpose, Spring Batch provides the`RetryListener` interface. The `RetryTemplate` lets users register `RetryListeners`, and
+they are given callbacks with `RetryContext` and `Throwable` where available during the
+iteration.
+
+The following code shows the interface definition for `RetryListener`:
+
+```
+public interface RetryListener {
+
+ boolean open(RetryContext context, RetryCallback callback);
+
+ void onError(RetryContext context, RetryCallback callback, Throwable throwable);
+
+ void close(RetryContext context, RetryCallback callback, Throwable throwable);
+}
+```
+
+The `open` and `close` callbacks come before and after the entire retry in the simplest
+case, and `onError` applies to the individual `RetryCallback` calls. The `close` method
+might also receive a `Throwable`. If there has been an error, it is the last one thrown by
+the `RetryCallback`.
+
+Note that, when there is more than one listener, they are in a list, so there is an order.
+In this case, `open` is called in the same order while `onError` and `close` are called in
+reverse order.
+
+### Declarative Retry
+
+Sometimes, there is some business processing that you know you want to retry every time it
+happens. The classic example of this is the remote service call. Spring Batch provides an
+AOP interceptor that wraps a method call in a `RetryOperations` implementation for just
+this purpose. The `RetryOperationsInterceptor` executes the intercepted method and retries
+on failure according to the `RetryPolicy` in the provided `RepeatTemplate`.
+
+The following example shows a declarative retry that uses the Spring AOP namespace to
+retry a service call to a method called `remoteCall` (for more detail on how to configure
+AOP interceptors, see the Spring User Guide):
+
+```
+
+
+
+
+ ...
+
+```
+
+When using java configuration, a `TaskExecutor` can be added to the step,
+as shown in the following example:
+
+Java Configuration
+
+```
+@Bean
+public TaskExecutor taskExecutor() {
+ return new SimpleAsyncTaskExecutor("spring_batch");
+}
+
+@Bean
+public Step sampleStep(TaskExecutor taskExecutor) {
+ return this.stepBuilderFactory.get("sampleStep")
+ .chunk(10)
+ .reader(itemReader())
+ .writer(itemWriter())
+ .taskExecutor(taskExecutor)
+ .build();
+}
+```
+
+In this example, the `taskExecutor` is a reference to another bean definition that
+implements the `TaskExecutor` interface.[`TaskExecutor`](https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/core/task/TaskExecutor.html)is a standard Spring interface, so consult the Spring User Guide for details of available
+implementations. The simplest multi-threaded `TaskExecutor` is a`SimpleAsyncTaskExecutor`.
+
+The result of the above configuration is that the `Step` executes by reading, processing,
+and writing each chunk of items (each commit interval) in a separate thread of execution.
+Note that this means there is no fixed order for the items to be processed, and a chunk
+might contain items that are non-consecutive compared to the single-threaded case. In
+addition to any limits placed by the task executor (such as whether it is backed by a
+thread pool), there is a throttle limit in the tasklet configuration which defaults to 4.
+You may need to increase this to ensure that a thread pool is fully utilized.
+
+For example you might increase the throttle-limit, as shown in the following example:
+
+```
+ ...
+
+```
+
+When using Java configuration, the builders provide access to the throttle limit, as shown
+in the following example:
+
+Java Configuration
+
+```
+@Bean
+public Step sampleStep(TaskExecutor taskExecutor) {
+ return this.stepBuilderFactory.get("sampleStep")
+ .chunk(10)
+ .reader(itemReader())
+ .writer(itemWriter())
+ .taskExecutor(taskExecutor)
+ .throttleLimit(20)
+ .build();
+}
+```
+
+Note also that there may be limits placed on concurrency by any pooled resources used in
+your step, such as a `DataSource`. Be sure to make the pool in those resources at least
+as large as the desired number of concurrent threads in the step.
+
+There are some practical limitations of using multi-threaded `Step` implementations for
+some common batch use cases. Many participants in a `Step` (such as readers and writers)
+are stateful. If the state is not segregated by thread, then those components are not
+usable in a multi-threaded `Step`. In particular, most of the off-the-shelf readers and
+writers from Spring Batch are not designed for multi-threaded use. It is, however,
+possible to work with stateless or thread safe readers and writers, and there is a sample
+(called `parallelJob`) in the[Spring
+Batch Samples](https://github.com/spring-projects/spring-batch/tree/master/spring-batch-samples) that shows the use of a process indicator (see[Preventing State Persistence](readersAndWriters.html#process-indicator)) to keep track
+of items that have been processed in a database input table.
+
+Spring Batch provides some implementations of `ItemWriter` and `ItemReader`. Usually,
+they say in the Javadoc if they are thread safe or not or what you have to do to avoid
+problems in a concurrent environment. If there is no information in the Javadoc, you can
+check the implementation to see if there is any state. If a reader is not thread safe,
+you can decorate it with the provided `SynchronizedItemStreamReader` or use it in your own
+synchronizing delegator. You can synchronize the call to `read()` and as long as the
+processing and writing is the most expensive part of the chunk, your step may still
+complete much faster than it would in a single threaded configuration.
+
+### Parallel Steps
+
+As long as the application logic that needs to be parallelized can be split into distinct
+responsibilities and assigned to individual steps, then it can be parallelized in a
+single process. Parallel Step execution is easy to configure and use.
+
+For example, executing steps `(step1,step2)` in parallel with `step3` is straightforward,
+as shown in the following example:
+
+```
+
+
+
+
+
+
+
+
+
+("splitFlow")
+ .split(taskExecutor())
+ .add(flow1(), flow2())
+ .build();
+}
+
+@Bean
+public Flow flow1() {
+ return new FlowBuilder("flow1")
+ .start(step1())
+ .next(step2())
+ .build();
+}
+
+@Bean
+public Flow flow2() {
+ return new FlowBuilder("flow2")
+ .start(step3())
+ .build();
+}
+
+@Bean
+public TaskExecutor taskExecutor() {
+ return new SimpleAsyncTaskExecutor("spring_batch");
+}
+```
+
+The configurable task executor is used to specify which `TaskExecutor`implementation should be used to execute the individual flows. The default is`SyncTaskExecutor`, but an asynchronous `TaskExecutor` is required to run the steps in
+parallel. Note that the job ensures that every flow in the split completes before
+aggregating the exit statuses and transitioning.
+
+See the section on [Split Flows](step.html#split-flows) for more detail.
+
+### Remote Chunking
+
+In remote chunking, the `Step` processing is split across multiple processes,
+communicating with each other through some middleware. The following image shows the
+pattern:
+
+
+
+Figure 1. Remote Chunking
+
+The manager component is a single process, and the workers are multiple remote processes.
+This pattern works best if the manager is not a bottleneck, so the processing must be more
+expensive than the reading of items (as is often the case in practice).
+
+The manager is an implementation of a Spring Batch `Step` with the `ItemWriter` replaced
+by a generic version that knows how to send chunks of items to the middleware as
+messages. The workers are standard listeners for whatever middleware is being used (for
+example, with JMS, they would be `MessageListener` implementations), and their role is
+to process the chunks of items using a standard `ItemWriter` or `ItemProcessor` plus`ItemWriter`, through the `ChunkProcessor` interface. One of the advantages of using this
+pattern is that the reader, processor, and writer components are off-the-shelf (the same
+as would be used for a local execution of the step). The items are divided up dynamically
+and work is shared through the middleware, so that, if the listeners are all eager
+consumers, then load balancing is automatic.
+
+The middleware has to be durable, with guaranteed delivery and a single consumer for each
+message. JMS is the obvious candidate, but other options (such as JavaSpaces) exist in
+the grid computing and shared memory product space.
+
+See the section on[Spring Batch Integration - Remote Chunking](spring-batch-integration.html#remote-chunking)for more detail.
+
+### Partitioning
+
+Spring Batch also provides an SPI for partitioning a `Step` execution and executing it
+remotely. In this case, the remote participants are `Step` instances that could just as
+easily have been configured and used for local processing. The following image shows the
+pattern:
+
+
+
+Figure 2. Partitioning
+
+The `Job` runs on the left-hand side as a sequence of `Step` instances, and one of the`Step` instances is labeled as a manager. The workers in this picture are all identical
+instances of a `Step`, which could in fact take the place of the manager, resulting in the
+same outcome for the `Job`. The workers are typically going to be remote services but
+could also be local threads of execution. The messages sent by the manager to the workers
+in this pattern do not need to be durable or have guaranteed delivery. Spring Batch
+metadata in the `JobRepository` ensures that each worker is executed once and only once for
+each `Job` execution.
+
+The SPI in Spring Batch consists of a special implementation of `Step` (called the`PartitionStep`) and two strategy interfaces that need to be implemented for the specific
+environment. The strategy interfaces are `PartitionHandler` and `StepExecutionSplitter`,
+and their role is shown in the following sequence diagram:
+
+
+
+Figure 3. Partitioning SPI
+
+The `Step` on the right in this case is the “remote” worker, so, potentially, there are
+many objects and or processes playing this role, and the `PartitionStep` is shown driving
+the execution.
+
+The following example shows the `PartitionStep` configuration when using XML
+configuration:
+
+```
+
+