# 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 (``).
#### Restartability
One key issue when executing a batch job concerns the behavior of a `Job` when it is
restarted. The launching of a `Job` is considered to be a 'restart' if a `JobExecution`already exists for the particular `JobInstance`. Ideally, all jobs should be able to start
up where they left off, but there are scenarios where this is not possible. *It is
entirely up to the developer to ensure that a new `JobInstance` is created in this
scenario.* However, Spring Batch does provide some help. If a `Job` should never be
restarted, but should always be run as part of a new `JobInstance`, then the
restartable property may be set to 'false'.
The following example shows how to set the `restartable` field to `false` in XML:
XML Configuration
```
```
The following example shows how to set the `restartable` field to `false` in Java:
Java Configuration
```
@Bean
public Job footballJob() {
return this.jobBuilderFactory.get("footballJob")
.preventRestart()
...
.build();
}
```
To phrase it another way, setting restartable to false means “this`Job` does not support being started again”. Restarting a `Job` that is not
restartable causes a `JobRestartException` to
be thrown.
```
Job job = new SimpleJob();
job.setRestartable(false);
JobParameters jobParameters = new JobParameters();
JobExecution firstExecution = jobRepository.createJobExecution(job, jobParameters);
jobRepository.saveOrUpdate(firstExecution);
try {
jobRepository.createJobExecution(job, jobParameters);
fail();
}
catch (JobRestartException e) {
// expected
}
```
This snippet of JUnit code shows how attempting to create a`JobExecution` the first time for a non restartable
job will cause no issues. However, the second
attempt will throw a `JobRestartException`.
#### Intercepting Job Execution
During the course of the execution of a
Job, it may be useful to be notified of various
events in its lifecycle so that custom code may be executed. The`SimpleJob` allows for this by calling a`JobListener` at the appropriate time:
```
public interface JobExecutionListener {
void beforeJob(JobExecution jobExecution);
void afterJob(JobExecution jobExecution);
}
```
`JobListeners` can be added to a `SimpleJob` by setting listeners on the job.
The following example shows how to add a listener element to an XML job definition:
XML Configuration
```
```
The following example shows how to add a listener method to a Java job definition:
Java Configuration
```
@Bean
public Job footballJob() {
return this.jobBuilderFactory.get("footballJob")
.listener(sampleListener())
...
.build();
}
```
It should be noted that the `afterJob` method is called regardless of the success or
failure of the `Job`. If success or failure needs to be determined, it can be obtained
from the `JobExecution`, as follows:
```
public void afterJob(JobExecution jobExecution){
if (jobExecution.getStatus() == BatchStatus.COMPLETED ) {
//job success
}
else if (jobExecution.getStatus() == BatchStatus.FAILED) {
//job failure
}
}
```
The annotations corresponding to this interface are:
* `@BeforeJob`
* `@AfterJob`
#### Inheriting from a Parent Job
If a group of Jobs share similar, but not
identical, configurations, then it may be helpful to define a "parent"`Job` from which the concrete
Jobs may inherit properties. Similar to class
inheritance in Java, the "child" `Job` will combine
its elements and attributes with the parent’s.
In the following example, "baseJob" is an abstract`Job` definition that defines only a list of
listeners. The `Job` "job1" is a concrete
definition that inherits the list of listeners from "baseJob" and merges
it with its own list of listeners to produce a`Job` with two listeners and one`Step`, "step1".
```
```
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
you have a class annotated with it, you will have all of the above available.|
|---|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
With the base configuration in place, a user can use the provided builder factories to
configure a job. The following example shows a two step job configured with the`JobBuilderFactory` and the `StepBuilderFactory`:
```
@Configuration
@EnableBatchProcessing
@Import(DataSourceConfiguration.class)
public class AppConfig {
@Autowired
private JobBuilderFactory jobs;
@Autowired
private StepBuilderFactory steps;
@Bean
public Job job(@Qualifier("step1") Step step1, @Qualifier("step2") Step step2) {
return jobs.get("myJob").start(step1).next(step2).build();
}
@Bean
protected Step step1(ItemReader 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
```
```
None of the configuration options listed above are required except the `id`. If they are
not set, the defaults shown above will be used. They are shown above for awareness
purposes. The `max-varchar-length` defaults to 2500, which is the length of the long`VARCHAR` columns in the [sample schema
scripts](schema-appendix.html#metaDataSchemaOverview).
When using java configuration, a `JobRepository` is provided for you. A JDBC based one is
provided out of the box if a `DataSource` is provided, the `Map` based one if not. However,
you can customize the configuration of the `JobRepository` through an implementation of the`BatchConfigurer` interface.
Java Configuration
```
...
// This would reside in your BatchConfigurer implementation
@Override
protected JobRepository createJobRepository() throws Exception {
JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
factory.setDataSource(dataSource);
factory.setTransactionManager(transactionManager);
factory.setIsolationLevelForCreate("ISOLATION_SERIALIZABLE");
factory.setTablePrefix("BATCH_");
factory.setMaxVarCharLength(1000);
return factory.getObject();
}
...
```
None of the configuration options listed above are required except
the dataSource and transactionManager. If they are not set, the defaults shown above
will be used. They are shown above for awareness purposes. The
max varchar length defaults to 2500, which is the
length of the long `VARCHAR` columns in the[sample schema scripts](schema-appendix.html#metaDataSchemaOverview)
#### Transaction Configuration for the JobRepository
If the namespace or the provided `FactoryBean` is used, transactional advice is
automatically created around the repository. This is to ensure that the batch meta-data,
including state that is necessary for restarts after a failure, is persisted correctly.
The behavior of the framework is not well defined if the repository methods are not
transactional. The isolation level in the `create*` method attributes is specified
separately to ensure that, when jobs are launched, if two processes try to launch
the same job at the same time, only one succeeds. The default isolation level for that
method is `SERIALIZABLE`, which is quite aggressive. `READ_COMMITTED` would work just as
well. `READ_UNCOMMITTED` would be fine if two processes are not likely to collide in this
way. However, since a call to the `create*` method is quite short, it is unlikely that`SERIALIZED` causes problems, as long as the database platform supports it. However, this
can be overridden.
The following example shows how to override the isolation level in XML:
XML Configuration
```
```
The following example shows how to override the isolation level 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.setTransactionManager(transactionManager);
factory.setIsolationLevelForCreate("ISOLATION_REPEATABLE_READ");
return factory.getObject();
}
```
If the namespace or factory beans are not used, then it is also essential to configure the
transactional behavior of the repository using AOP.
The following example shows how to configure the transactional behavior of the repository
in XML:
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 how to change the table prefix 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.setTransactionManager(transactionManager);
factory.setTablePrefix("SYSTEM.TEST_");
return factory.getObject();
}
```
Given the preceding changes, every query to the meta-data tables is prefixed with`SYSTEM.TEST_`. `BATCH_JOB_EXECUTION` is referred to as SYSTEM.`TEST_JOB_EXECUTION`.
| |Only the table prefix is configurable. The table and column names are not.|
|---|--------------------------------------------------------------------------|
#### In-Memory Repository
There are scenarios in which you may not want to persist your domain objects to the
database. One reason may be speed; storing domain objects at each commit point takes extra
time. Another reason may be that you just don’t need to persist status for a particular
job. For this reason, Spring batch provides an in-memory `Map` version of the job
repository.
The following example shows the inclusion of `MapJobRepositoryFactoryBean` 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
for removal in v5. If you want to use an in-memory job repository, you can use an embedded database
like H2, Apache Derby or HSQLDB. There are several ways to create an embedded database and use it in
your Spring Batch application. One way to do that is by using the APIs from [Spring JDBC](https://docs.spring.io/spring-framework/docs/current/reference/html/data-access.html#jdbc-embedded-database-support):
```
@Bean
public DataSource dataSource() {
return new EmbeddedDatabaseBuilder()
.setType(EmbeddedDatabaseType.H2)
.addScript("/org/springframework/batch/core/schema-drop-h2.sql")
.addScript("/org/springframework/batch/core/schema-h2.sql")
.build();
}
```
Once you have defined your embedded datasource as a bean in your application context, it should be picked
up automatically if you use `@EnableBatchProcessing`. Otherwise you can configure it manually using the
JDBC based `JobRepositoryFactoryBean` as shown in the [Configuring a JobRepository section](#configuringJobRepository).|
|---|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
#### Non-standard Database Types in a Repository
If you are using a database platform that is not in the list of supported platforms, you
may be able to use one of the supported types, if the SQL variant is close enough. To do
this, you can use the raw `JobRepositoryFactoryBean` instead of the namespace shortcut and
use it to set the database type to the closest match.
The following example shows how to use `JobRepositoryFactoryBean` to set the database type
to the closest match in XML:
XML Configuration
```
```
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
create an `ApplicationContext`. This file
should contain everything needed to run the complete
Job|
|-------|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
|jobName| The name of the job to be run. |
These arguments must be passed in with the path first and the name second. All arguments
after these are considered to be job parameters, are turned into a JobParameters object,
and must be in the format of 'name=value'.
The following example shows a date passed as a job parameter to a job defied in XML:
```
key/value pairs to identifying job parameters. However, it is possible to explicitly specify
which job parameters are identifying and which are not by prefixing them with `+` or `-` respectively.
In the following example, `schedule.date` is an identifying job parameter while `vendor.id` is not:
```
+schedule.date(date)=2007/05/05 -vendor.id=123
```
```
+schedule.date(date)=2007/05/05 -vendor.id=123
```
This behaviour can be overridden by using a custom `JobParametersConverter`.|
|---|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
In most cases, you would want to use a manifest to declare your main class in a jar, but,
for simplicity, the class was used directly. This example is using the same 'EndOfDay'
example from the [domainLanguageOfBatch](domain.html#domainLanguageOfBatch). The first
argument is 'endOfDayJob.xml', which is the Spring ApplicationContext containing the`Job`. The second argument, 'endOfDay' represents the job name. The final argument,
'schedule.date(date)=2007/05/05', is converted into a JobParameters object.
The following example shows a sample configuration for `endOfDay` in XML:
```
```
In most cases you would want to use a manifest to declare your main class in a jar, but,
for simplicity, the class was used directly. This example is using the same 'EndOfDay'
example from the [domainLanguageOfBatch](domain.html#domainLanguageOfBatch). The first
argument is 'io.spring.EndOfDayJobConfiguration', which is the fully qualified class name
to the configuration class containing the Job. The second argument, 'endOfDay' represents
the job name. The final argument, 'schedule.date(date)=2007/05/05' is converted into a`JobParameters` object. An example of the java configuration follows:
The following example shows a sample configuration for `endOfDay` in Java:
```
@Configuration
@EnableBatchProcessing
public class EndOfDayJobConfiguration {
@Autowired
private JobBuilderFactory jobBuilderFactory;
@Autowired
private StepBuilderFactory stepBuilderFactory;
@Bean
public Job endOfDay() {
return this.jobBuilderFactory.get("endOfDay")
.start(step1())
.build();
}
@Bean
public Step step1() {
return this.stepBuilderFactory.get("step1")
.tasklet((contribution, chunkContext) -> null)
.build();
}
}
```
The preceding example is overly simplistic, since there are many more requirements to a
run a batch job in Spring Batch in general, but it serves to show the two main
requirements of the `CommandLineJobRunner`: `Job` and `JobLauncher`.
##### ExitCodes
When launching a batch job from the command-line, an enterprise
scheduler is often used. Most schedulers are fairly dumb and work only
at the process level. This means that they only know about some
operating system process such as a shell script that they’re invoking.
In this scenario, the only way to communicate back to the scheduler
about the success or failure of a job is through return codes. A
return code is a number that is returned to a scheduler by the process
that indicates the result of the run. In the simplest case: 0 is
success and 1 is failure. However, there may be more complex
scenarios: If job A returns 4 kick off job B, and if it returns 5 kick
off job C. This type of behavior is configured at the scheduler level,
but it is important that a processing framework such as Spring Batch
provide a way to return a numeric representation of the 'Exit Code'
for a particular batch job. In Spring Batch this is encapsulated
within an `ExitStatus`, which is covered in more
detail in Chapter 5. For the purposes of discussing exit codes, the
only important thing to know is that an`ExitStatus` has an exit code property that is
set by the framework (or the developer) and is returned as part of the`JobExecution` returned from the`JobLauncher`. The`CommandLineJobRunner` converts this string value
to a number using the `ExitCodeMapper`interface:
```
public interface ExitCodeMapper {
public int intValue(String exitCode);
}
```
The essential contract of an`ExitCodeMapper` is that, given a string exit
code, a number representation will be returned. The default implementation used by the job runner is the `SimpleJvmExitCodeMapper`that returns 0 for completion, 1 for generic errors, and 2 for any job
runner errors such as not being able to find a`Job` in the provided context. If anything more
complex than the 3 values above is needed, then a custom
implementation of the `ExitCodeMapper` interface
must be supplied. Because the`CommandLineJobRunner` is the class that creates
an `ApplicationContext`, and thus cannot be
'wired together', any values that need to be overwritten must be
autowired. This means that if an implementation of`ExitCodeMapper` is found within the `BeanFactory`,
it will be injected into the runner after the context is created. All
that needs to be done to provide your own`ExitCodeMapper` is to declare the implementation
as a root level bean and ensure that it is part of the`ApplicationContext` that is loaded by the
runner.
#### Running Jobs from within a Web Container
Historically, offline processing such as batch jobs have been
launched from the command-line, as described above. However, there are
many cases where launching from an `HttpRequest` is
a better option. Many such use cases include reporting, ad-hoc job
running, and web application support. Because a batch job by definition
is long running, the most important concern is ensuring to launch the
job asynchronously:
Figure 4. Asynchronous Job Launcher Sequence From Web Container
The controller in this case is a Spring MVC controller. More
information on Spring MVC can be found here: .
The controller launches a `Job` using a`JobLauncher` that has been configured to launch[asynchronously](#runningJobsFromWebContainer), which
immediately returns a `JobExecution`. The`Job` will likely still be running, however, this
nonblocking behaviour allows the controller to return immediately, which
is required when handling an `HttpRequest`. An
example is below:
```
@Controller
public class JobLauncherController {
@Autowired
JobLauncher jobLauncher;
@Autowired
Job job;
@RequestMapping("/jobLauncher.html")
public void handle() throws Exception{
jobLauncher.run(job, new JobParameters());
}
}
```
### Advanced Meta-Data Usage
So far, both the `JobLauncher` and `JobRepository` interfaces have been
discussed. Together, they represent simple launching of a job, and basic
CRUD operations of batch domain objects:
Figure 5. Job Repository
A `JobLauncher` uses the`JobRepository` to create new`JobExecution` objects and run them.`Job` and `Step` implementations
later use the same `JobRepository` for basic updates
of the same executions during the running of a Job.
The basic operations suffice for simple scenarios, but in a large batch
environment with hundreds of batch jobs and complex scheduling
requirements, more advanced access of the meta data is required:
Figure 6. Advanced Job Repository Access
The `JobExplorer` and`JobOperator` interfaces, which will be discussed
below, add additional functionality for querying and controlling the meta
data.
#### Querying the Repository
The most basic need before any advanced features is the ability to
query the repository for existing executions. This functionality is
provided by the `JobExplorer` interface:
```
public interface JobExplorer {
List 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 configure a `JobExplorer` in Java:
Java Configuration
```
...
// This would reside in your BatchConfigurer implementation
@Override
public JobExplorer getJobExplorer() throws Exception {
JobExplorerFactoryBean factoryBean = new JobExplorerFactoryBean();
factoryBean.setDataSource(this.dataSource);
return factoryBean.getObject();
}
...
```
[Earlier in this chapter](#repositoryTablePrefix), we noted that the table prefix
of the `JobRepository` can be modified to allow for different versions or schemas. Because
the `JobExplorer` works with the same tables, it too needs the ability to set a prefix.
The following example shows how to set the table prefix for a `JobExplorer` in XML:
XML Configuration
```
```
The following example shows how to set the table prefix for a `JobExplorer` in Java:
Java Configuration
```
...
// This would reside in your BatchConfigurer implementation
@Override
public JobExplorer getJobExplorer() throws Exception {
JobExplorerFactoryBean factoryBean = new JobExplorerFactoryBean();
factoryBean.setDataSource(this.dataSource);
factoryBean.setTablePrefix("SYSTEM.");
return factoryBean.getObject();
}
...
```
#### JobRegistry
A `JobRegistry` (and its parent interface `JobLocator`) is not mandatory, but it can be
useful if you want to keep track of which jobs are available in the context. It is also
useful for collecting jobs centrally in an application context when they have been created
elsewhere (for example, in child contexts). Custom `JobRegistry` implementations can also
be used to manipulate the names and other properties of the jobs that are registered.
There is only one implementation provided by the framework and this is based on a simple
map from job name to job instance.
The following example shows how to include a `JobRegistry` for a job defined in XML:
```
```
The following example shows how to include a `JobRegistry` for a job defined in Java:
When using `@EnableBatchProcessing`, a `JobRegistry` is provided out of the box for you.
If you want to configure your own:
```
...
// This is already provided via the @EnableBatchProcessing but can be customized via
// overriding the getter in the SimpleBatchConfiguration
@Override
@Bean
public JobRegistry jobRegistry() throws Exception {
return new MapJobRegistry();
}
...
```
There are two ways to populate a `JobRegistry` automatically: using
a bean post processor and using a registrar lifecycle component. These
two mechanisms are described in the following sections.
##### JobRegistryBeanPostProcessor
This is a bean post-processor that can register all jobs as they are created.
The following example shows how to include the `JobRegistryBeanPostProcessor` for a job
defined 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.