whats-new.adoc

[[spring-whats-new]]
= What's New in Spring Framework 4.x


[[new-in-4.0]]
== New Features and Enhancements in Spring Framework 4.0
The Spring Framework was first released in 2004; since then there have been significant
major revisions: Spring 2.0 provided XML namespaces and AspectJ support; Spring 2.5
embraced annotation-driven configuration; Spring 3.0 introduced a strong Java 5+ foundation
across the framework codebase, and features such as the Java-based `@Configuration` model.

Version 4.0 is the latest major release of the Spring Framework and the first to fully
support Java 8 features. You can still use Spring with older versions of Java, however,
the minimum requirement has now been raised to Java SE 6. We have also taken the
opportunity of a major release to remove many deprecated classes and methods.

A https://github.com/spring-projects/spring-framework/wiki/Migrating-from-earlier-versions-of-the-spring-framework[migration guide for upgrading to Spring 4.0]
is available on the https://github.com/spring-projects/spring-framework/wiki[Spring Framework GitHub Wiki].




=== Improved Getting Started Experience
The new https://spring.io[spring.io] website provides a whole series of
https://spring.io/guides["Getting Started"] guides to help you learn Spring. You
can read more about the guides in the <<overview-getting-started-with-spring>> section
in this document. The new website also provides a comprehensive overview of the many
additional projects that are released under the Spring umbrella.

If you are a Maven user you may also be interested in the helpful
<<overview-maven-bom,bill of materials>> POM file that is now published with each Spring
Framework release.




=== Removed Deprecated Packages and Methods
All deprecated packages, and many deprecated classes and methods have been removed with
version 4.0. If you are upgrading from a previous release of Spring, you should ensure
that you have fixed any deprecated calls that you were making to outdated APIs.

For a complete set of changes, check out the
http://docs.spring.io/spring-framework/docs/3.2.4.RELEASE_to_4.0.0.RELEASE/[API
Differences Report].

Note that optional third-party dependencies have been raised to a 2010/2011 minimum
(i.e. Spring 4 generally only supports versions released in late 2010 or later now):
notably, Hibernate 3.6+, EhCache 2.1+, Quartz 1.8+, Groovy 1.8+, and Joda-Time 2.0+.
As an exception to the rule, Spring 4 requires the recent Hibernate Validator 4.3+,
and support for Jackson has been focused on 2.0+ now (with Jackson 1.8/1.9 support
retained for the time being where Spring 3.2 had it; now just in deprecated form).




=== Java 8 (as well as 6 and 7)
Spring Framework 4.0 provides support for several Java 8 features. You can make use of
__lambda expressions__ and __method references__ with Spring's callback interfaces. There
is first-class support for `java.time` (http://jcp.org/en/jsr/detail?id=310[JSR-310]),
and several existing annotations have been retrofitted as `@Repeatable`. You can also
use Java 8's parameter name discovery (based on the `-parameters` compiler flag) as an
alternative to compiling your code with debug information enabled.

Spring remains compatible with older versions of Java and the JDK: concretely, Java SE 6
(specifically, a minimum level equivalent to JDK 6 update 18, as released in January 2010)
and above are still fully supported. However, for newly started development projects
based on Spring 4, we recommend the use of Java 7 or 8.




=== Java EE 6 and 7
Java EE version 6 or above is now considered the baseline for Spring Framework 4, with
the JPA 2.0 and Servlet 3.0 specifications being of particular relevance. In order to
remain compatible with Google App Engine and older application servers, it is possible
to deploy a Spring 4 application into a Servlet 2.5 environment. However, Servlet 3.0+
is strongly recommended and a prerequisite in Spring's test and mock packages for test
setups in development environments.

[NOTE]
====
If you are a WebSphere 7 user, be sure to install the JPA 2.0 feature pack. On
WebLogic 10.3.4 or higher, install the JPA 2.0 patch that comes with it. This turns
both of those server generations into Spring 4 compatible deployment environments.
====

On a more forward-looking note, Spring Framework 4.0 supports the Java EE 7 level of
applicable specifications now: in particular, JMS 2.0, JTA 1.2, JPA 2.1, Bean Validation
1.1, and JSR-236 Concurrency Utilities. As usual, this support focuses on individual
use of those specifications, e.g. on Tomcat or in standalone environments. However,
it works equally well when a Spring application is deployed to a Java EE 7 server.

Note that Hibernate 4.3 is a JPA 2.1 provider and therefore only supported as of
Spring Framework 4.0. The same applies to Hibernate Validator 5.0 as a Bean Validation
1.1 provider. Neither of the two are officially supported with Spring Framework 3.2.



[[groovy-bean-definition-dsl]]
=== Groovy Bean Definition DSL
Beginning with Spring Framework 4.0, it is possible to define external bean configuration
using a Groovy DSL. This is similar in concept to using XML bean definitions but allows
for a more concise syntax. Using Groovy also allows you to easily embed bean definitions
directly in your bootstrap code. For example:

[source,groovy,indent=0]
[subs="verbatim,quotes"]
----
	def reader = new GroovyBeanDefinitionReader(myApplicationContext)
	reader.beans {
		dataSource(BasicDataSource) {
			driverClassName = "org.hsqldb.jdbcDriver"
			url = "jdbc:hsqldb:mem:grailsDB"
			username = "sa"
			password = ""
			settings = [mynew:"setting"]
		}
		sessionFactory(SessionFactory) {
			dataSource = dataSource
		}
		myService(MyService) {
			nestedBean = { AnotherBean bean ->
				dataSource = dataSource
			}
		}
	}
----

For more information consult the `GroovyBeanDefinitionReader`
{javadoc-baseurl}/org/springframework/beans/factory/groovy/GroovyBeanDefinitionReader.html[javadocs].




=== Core Container Improvements
There have been several general improvements to the core container:

* Spring now treats <<beans-generics-as-qualifiers,__generic types__ as a form of
  __qualifier__>> when injecting Beans. For example, if you are using a Spring Data
  `Repository` you can now easily inject a specific implementation:
  `@Autowired Repository<Customer> customerRepository`.
* If you use Spring's meta-annotation support, you can now develop custom annotations that
  <<beans-meta-annotations,expose specific attributes from the source annotation>>.
* Beans can now be __ordered__ when they are <<beans-autowired-annotation,autowired into
  lists and arrays>>. Both the `@Order` annotation and `Ordered` interface are
  supported.
* The `@Lazy` annotation can now be used on injection points, as well as on `@Bean`
  definitions.
* The <<beans-java-bean-description,`@Description` annotation has been introduced>> for
  developers using Java-based configuration.
* A generalized model for <<beans-java-conditional,conditionally filtering beans>> has
  been added via the `@Conditional` annotation. This is similar to `@Profile` support but
  allows for user-defined strategies to be developed programmatically.
* <<aop-pfb-proxy-types,CGLIB-based proxy classes>> no longer require a default
  constructor. Support is provided via the http://code.google.com/p/objenesis/[objenesis]
  library which is repackaged __inline__ and distributed as part of the Spring Framework.
  With this strategy, no constructor at all is being invoked for proxy instances anymore.
* There is managed time zone support across the framework now, e.g. on `LocaleContext`.




=== General Web Improvements
Deployment to Servlet 2.5 servers remains an option, but Spring Framework 4.0 is now
focused primarily on Servlet 3.0+ environments. If you are using the
<<spring-mvc-test-framework,Spring MVC Test Framework>> you
will need to ensure that a Servlet 3.0 compatible JAR is in your __test classpath__.

In addition to the WebSocket support mentioned later, the following general improvements
have been made to Spring's Web modules:

* You can use the <<mvc-ann-restcontroller,new `@RestController` annotation>> with Spring
  MVC applications, removing the need to add `@ResponseBody` to each of your
  `@RequestMapping` methods.
* The `AsyncRestTemplate` class has been added, <<rest-async-resttemplate,allowing
  non-blocking asynchronous support>> when developing REST clients.
* Spring now offers <<mvc-timezone,comprehensive timezone support>> when developing
  Spring MVC applications.




=== WebSocket, SockJS, and STOMP Messaging
A new `spring-websocket` module provides comprehensive support for WebSocket-based,
two-way communication between client and server in web applications. It is compatible with
http://jcp.org/en/jsr/detail?id=356[JSR-356], the Java WebSocket API, and in addition
provides SockJS-based fallback options (i.e. WebSocket emulation) for use in browsers
that don't yet support the WebSocket protocol (e.g. Internet Explorer < 10).

A new `spring-messaging` module adds support for STOMP as the WebSocket sub-protocol
to use in applications along with an annotation programming model for routing and
processing STOMP messages from WebSocket clients. As a result an `@Controller`
can now contain both `@RequestMapping` and `@MessageMapping` methods for handling
HTTP requests and messages from WebSocket-connected clients. The new `spring-messaging`
module also contains key abstractions formerly from the
http://projects.spring.io/spring-integration/[Spring Integration] project such as
`Message`, `MessageChannel`, `MessageHandler`, and others to serve as a foundation
for messaging-based applications.

For further details, including a more thorough introduction, see the <<websocket>> section.




=== Testing Improvements
In addition to pruning of deprecated code within the `spring-test` module, Spring
Framework 4.0 introduces several new features for use in unit and integration testing.

* Almost all annotations in the `spring-test` module (e.g., `@ContextConfiguration`,
  `@WebAppConfiguration`, `@ContextHierarchy`, `@ActiveProfiles`, etc.) can now be used
  as <<integration-testing-annotations-meta,meta-annotations>> to create custom
  _composed annotations_ and reduce configuration duplication across a test suite.
* Active bean definition profiles can now be resolved programmatically, simply by
  implementing a custom <<testcontext-ctx-management-env-profiles-ActiveProfilesResolver,`ActiveProfilesResolver`>>
  and registering it via the `resolver` attribute of `@ActiveProfiles`.
* A new `SocketUtils` class has been introduced in the `spring-core` module
  which enables you to scan for free TCP and UDP server ports on localhost. This
  functionality is not specific to testing but can prove very useful when writing
  integration tests that require the use of sockets, for example tests that start
  an in-memory SMTP server, FTP server, Servlet container, etc.
* As of Spring 4.0, the set of mocks in the `org.springframework.mock.web` package is
  now based on the Servlet 3.0 API. Furthermore, several of the Servlet API mocks
  (e.g., `MockHttpServletRequest`, `MockServletContext`, etc.) have been updated with
  minor enhancements and improved configurability.




[[new-in-4.1]]
== New Features and Enhancements in Spring Framework 4.1

=== JMS Improvements
Spring 4.1 introduces a much simpler infrastructure <<jms-annotated,to register JMS
listener endpoints>> by annotating bean methods with
{javadoc-baseurl}/org/springframework/jms/annotation/JmsListener.html[`@JmsListener`].
The XML namespace has been enhanced to support this new style (`jms:annotation-driven`),
and it is also possible to fully configure the infrastructure using Java config
({javadoc-baseurl}/org/springframework/jms/annotation/EnableJms.html[`@EnableJms`],
`JmsListenerContainerFactory`). It is also possible to register listener endpoints
programmatically using
{javadoc-baseurl}/org/springframework/jms/annotation/JmsListenerConfigurer.html[`JmsListenerConfigurer`].

Spring 4.1 also aligns its JMS support to allow you to benefit from the `spring-messaging`
abstraction introduced in 4.0, that is:

* Message listener endpoints can have a more flexible signature and benefit from
  standard messaging annotations such as `@Payload`, `@Header`, `@Headers`, and `@SendTo`. It
  is also possible to use a standard `Message` in lieu of `javax.jms.Message` as method
  argument.
* A new {javadoc-baseurl}/org/springframework/jms/core/JmsMessageOperations.html[`JmsMessageOperations`]
  interface is available and permits `JmsTemplate` like operations using the `Message`
  abstraction.

Finally, Spring 4.1 provides additional miscellaneous improvements:

* Synchronous request-reply operations support in `JmsTemplate`
* Listener priority can be specified per `<jms:listener/>` element
* Recovery options for the message listener container are configurable using a
  {javadoc-baseurl}/org/springframework/util/backoff/BackOff.html[`BackOff`] implementation
* JMS 2.0 shared consumers are supported

=== Caching Improvements

Spring 4.1 supports <<cache-jsr-107,JCache (JSR-107) annotations>> using Spring's
existing cache configuration and infrastructure abstraction; no changes are required
to use the standard annotations.

Spring 4.1 also improves its own caching abstraction significantly:

* Caches can be resolved at runtime using a
  <<cache-annotations-cacheable-cache-resolver,`CacheResolver`>>. As a result the
  `value` argument defining the cache name(s) to use is no longer mandatory.
* More operation-level customizations: cache resolver, cache manager, key
  generator
* A new <<cache-annotations-config,`@CacheConfig` class-level annotation>> allows
  common settings to be shared at the class level **without** enabling any cache operation.
* Better exception handling of cached methods using `CacheErrorHandler`

Spring 4.1 also has a breaking change in the `CacheInterface` as a new `putIfAbsent`
method has been added.

=== Web Improvements

* The existing support for resource handling based on the `ResourceHttpRequestHandler`
  has been expanded with new abstractions `ResourceResolver`, `ResourceTransformer`,
  and `ResourceUrlProvider`. A number of built-in implementations provide support
  for versioned resource URLs (for effective HTTP caching), locating gzipped resources,
  generating an HTML 5 AppCache manifests, and more. See <<mvc-config-static-resources>>.
* JDK 1.8's `java.util.Optional` is now supported for `@RequestParam`, `@RequestHeader`,
  and `@MatrixVariable` controller method arguments.
* `ListenableFuture` is supported as a return value alternative to `DeferredResult`
  where an underlying service (or perhaps a call to `AsyncRestTemplate`) already
  returns `ListenableFuture`.
* `@ModelAttribute` methods are now invoked in an order that respects inter-dependencies.
  See https://jira.spring.io/browse/SPR-6299[SPR-6299].
* Jackson's `@JsonView` is supported directly on `@ResponseBody` and `ResponseEntity`
  controller methods for serializing different amounts of detail for the same POJO (e.g.
  summary vs. detail page). This is also supported with View-based rendering by
  adding the serialization view type as a model attribute under a special key.
  See <<mvc-ann-jsonview>> for details.
* JSONP is now supported with Jackson. See <<mvc-ann-jsonp>>.
* A new lifecycle option is available for intercepting `@ResponseBody` and `ResponseEntity`
  methods just after the controller method returns and before the response is written.
  To take advantage declare an `@ControllerAdvice` bean that implements `ResponseBodyAdvice`.
  The built-in support for `@JsonView` and JSONP take advantage of this.
  See <<mvc-handlermapping-interceptor>>.
* There are three new `HttpMessageConverter` options:
** Gson -- lighter footprint than Jackson; has already been in use in Spring Android.
** Google Protocol Buffers -- efficient and effective as an inter-service communication
   data protocol within an enterprise but can also be exposed as JSON and XML for browsers.
** Jackson based XML serialization is now supported through the
  https://github.com/FasterXML/jackson-dataformat-xml[jackson-dataformat-xml] extension.
  When using `@EnableWebMvc` or `<mvc:annotation-driven/>`, this is used by default
  instead of JAXB2 if `jackson-dataformat-xml` is in the classpath.
* Views such as JSPs can now build links to controllers by referring to controller mappings
  by name. A default name is assigned to every `@RequestMapping`. For example `FooController`
  with method `handleFoo` is named "FC#handleFoo". The naming strategy is pluggable.
  It is also possible to name an `@RequestMapping` explicitly through its name attribute.
  A new `mvcUrl` function in the Spring JSP tag library makes this easy to use in JSP pages.
  See <<mvc-links-to-controllers-from-views>>.
* `ResponseEntity` provides a builder-style API to guide controller methods
  towards the preparation of server-side responses, e.g. `ResponseEntity.ok()`.
* `RequestEntity` is a new type that provides a builder-style API to guide client-side REST
  code towards the preparation of HTTP requests.
* MVC Java config and XML namespace:
** View resolvers can now be configured including support for content
   negotiation, see <<mvc-config-view-resolvers>>.
** View controllers now have built-in support for redirects and for setting the response
   status. An application can use this to configure redirect URLs, render 404 responses
   with a view, send "no content" responses, etc.
   Some use cases are
   https://jira.spring.io/browse/SPR-11543?focusedCommentId=100308&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-100308[listed here].
** Path matching customizations are frequently used and now built-in.
   See <<mvc-config-path-matching>>.
* http://groovy-lang.org/docs/groovy-2.3.6/html/documentation/markup-template-engine.html[Groovy markup template]
  support (based on Groovy 2.3). See the `GroovyMarkupConfigurer` and respecitve
  `ViewResolver` and `View' implementations.

=== WebSocket Messaging Improvements

* SockJS (Java) client-side support. See `SockJsClient` and classes in same package.
* New application context events `SessionSubscribeEvent` and `SessionUnsubscribeEvent` published
  when STOMP clients subscribe and unsubscribe.
* New "websocket" scope. See <<websocket-stomp-websocket-scope>>.
* `@SendToUser` can target only a single session and does not require an authenticated user.
* `@MessageMapping` methods can use dot "." instead of slash "/" as path separator.
  See https://jira.spring.io/browse/SPR-11660[SPR-11660].
* STOMP/WebSocket monitoring info collected and logged. See <<websocket-stomp-stats>>.
* Significantly optimized and improved logging that should remain very readable
  and compact even at DEBUG level.
* Optimized message creation including support for temporary message mutability
  and avoiding automatic message id and timestamp creation. See Javadoc of
  `MessageHeaderAccessor`.
* Close STOMP/WebSocket connections that have no activity within 60 seconds after the
  WebSocket session is established. See https://jira.spring.io/browse/SPR-11884[SPR-11884].

=== Testing Improvements

* Groovy scripts can now be used to configure the `ApplicationContext` loaded for
  integration tests in the TestContext framework.
** See <<testcontext-ctx-management-groovy>> for details.
* Test-managed transactions can now be programmatically started and ended within
  transactional test methods via the new `TestTransaction` API.
** See <<testcontext-tx-programmatic-tx-mgt>> for details.
* SQL script execution can now be configured declaratively via the new `@Sql` and
  `@SqlConfig` annotations on a per-class or per-method basis.
** See <<testcontext-executing-sql>> for details.
* Test property sources which automatically override system and application property
  sources can be configured via the new `@TestPropertySource` annotation.
** See <<testcontext-ctx-management-property-sources>> for details.
* Default ++TestExecutionListener++s can now be automatically discovered.
** See <<testcontext-tel-config-automatic-discovery>> for details.
* Custom ++TestExecutionListener++s can now be automatically merged with the default
  listeners.
** See <<testcontext-tel-config-merging>> for details.
* The documentation for transactional testing support in the TestContext framework has
  been improved with more thorough explanations and additional examples.
** See <<testcontext-tx>> for details.
* Various improvements to `MockServletContext`, `MockHttpServletRequest`, and other
  Servlet API mocks.
* `AssertThrows` has been refactored to support `Throwable` instead of `Exception`.
* In Spring MVC Test, JSON responses can be asserted with https://github.com/skyscreamer/JSONassert[JSON Assert]
  as an extra option to using JSONPath much like it has been possible to do for XML with
  XMLUnit.
* `MockMvcBuilder` _recipes_ can now be created with the help of `MockMvcConfigurer`. This
  was added to make it easy to apply Spring Security setup but can be used to encapsulate
  common setup for any 3rd party framework or within a project.
* `MockRestServiceServer` now supports the `AsyncRestTemplate` for client-side testing.



[[new-in-4.2]]
== New Features and Enhancements in Spring Framework 4.2

=== Core Container Improvements

* The application event infrastructure now offers an <<context-functionality-events-annotation,
  annotation-based model>> as well as the ability to publish any arbitrary event.
** Any public method in a managed bean can be annotated with `@EventListener` to consume events.
** `@TransactionalEventListener` provides transaction-bound event support.
* Spring Framework 4.2 introduces first-class support for declaring and
  looking up aliases for annotation attributes. The new `@AliasFor`
  annotation can be used to declare a pair of aliased attributes within
  a single annotation or to declare an alias from one attribute in a
  custom composed annotation to an attribute in a meta-annotation.
** The following annotations have been retrofitted with `@AliasFor`
   support: `@ManagedResource`, `@ContextConfiguration`,
   `@ActiveProfiles`, `@TestExecutionListeners`, `@TestPropertySource`,
   `@Sql`, `@ControllerAdvice`, `@RequestMapping`.
** For example, `@ContextConfiguration` from the `spring-test` module
   is now declared as follows:
[source,java,indent=0]
[subs="verbatim,quotes"]
----
public @interface ContextConfiguration {
 
    @AliasFor(attribute = "locations")
    String[] value() default {};
 
    @AliasFor(attribute = "value")
    String[] locations() default {};
 
    // ...
}
----
** Similarly, _composed annotations_ that override attributes from
   meta-annotations can now use `@AliasFor` for fine-grained control
   over exactly which attributes are overridden within an annotation
   hierarchy. In fact, it is now possible to declare an alias for the
   `value` attribute of a meta-annotation.
** For example, one can now develop a composed annotation with a custom 
   attribute override as follows.
[source,java,indent=0]
[subs="verbatim,quotes"]
----
@ContextConfiguration
public @interface MyTestConfig {
 
    @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")
    String[] xmlFiles();
 
    // ...
}
----
* Numerous improvements to Spring's search algorithms used for finding
  meta-annotations. For example, locally declared _composed annotations_
  are now favored over inherited annotations.
* _Composed annotations_ that override attributes from meta-annotations
  can now be discovered on interfaces and on abstract, bridge, & interface
  methods as well as on classes, standard methods, constructors, and 
  fields.
* The features of field-based data binding (`DirectFieldAccessor`) have been aligned with the current
  property-based data binding (`BeanWrapper`). In particular, field-based binding now supports
  navigation for Collections, Arrays, and Maps.
* `DefaultConversionService` now provides out-of-the-box converters for `Stream`, `Charset`,
  `Currency`, and `TimeZone`. Such converters can be added individually to any arbitrary
  `ConversionService` as well.
* `JavaMailSenderImpl` has a new `testConnection()` method for checking connectivity to the server.
* `ScheduledTaskRegistrar` exposes scheduled tasks.
* Apache `commons-pool2` is now supported.
* `@NumberFormat` can now be used as a meta-annotation.

=== Data Access Improvements

* Embedded databases can now be automatically assigned unique names, and
  `<jdbc:embedded-database>` supports a new `database-name` attribute.
  See "Testing Improvements" below for further details.
* `SimpleJdbcCallOperations` now supports named binding.
* `javax.transaction.Transactional` is now supported via AspectJ.

=== JMS Improvements

* The `autoStartup` attribute can be controlled via `JmsListenerContainerFactory`.
* The type of the reply `Destination` can now be configured per listener container.
* The value of the `@SendTo` annotation can now use a SpEL expression.

=== Web Improvements

* HTTP Streaming and Server-Sent Events support, see <<mvc-ann-async-http-streaming>>.
* Built-in support for CORS including global (MVC Java config) and local (e.g. `@CrossOrigin`) configuration.
* HTTP caching updates:
** new `CacheControl` builder; plug into `WebContentGenerator`, `ResourceHttpRequestHandler`, `ResponseEntity`.
** improved ETag/Last-Modified support in `WebRequest`.
* JavaScript view templating built on Nashorn and JDK 1.8, see `ScriptTemplateViewResolver`.
* Custom `@RequestMapping` annotations.
* Public methods in `AbstractHandlerMethodMapping` to register and unregister request mappings at runtime.
* New `RequestBodyAdvice` extension point and a built-in implementation to support Jackson's `@JsonView`
  on`@RequestBody` method arguments.
* `HandlerMethod` as a method argument on `@ExceptionHandler` methods, especially
  handy in `@ControllerAdvice` components.
* `java.util.concurrent.CompletableFuture` as an `@Controller` method return value type.
* Byte-range request support in `HttpHeaders` and for serving static resources.
* `@ResponseStatus` detected on nested exceptions.
* `UriTemplateHandler` extension point in the `RestTemplate`.
** `DefaultUriTemplateHandler` exposes `baseUrl` property and path segment encoding options.
** the extension point can also be used to plug in any URI template library.
* http://square.github.io/okhttp/[OkHTTP] integration with the `RestTemplate`.
* Custom `baseUrl" alternative for methods in `MvcUriComponentsBuilder`.

=== WebSocket Messaging Improvements

* Expose presence information about connected users and subscriptions:
** new `SimpUserRegistry` exposed as a bean named "userRegistry".
** sharing of presence information across cluster of servers (see broker relay config options).
* Resolve user destinations across cluster of servers (see broker relay config options).
* `StompSubProtocolErrorHandler` extension point to customize and control STOMP ERROR frames to clients.
* Global `@MessageExceptionHandler` methods via `@ControllerAdvice` components.
* Heart-beats and a SpEL expression 'selector' header for subscriptions with `SimpleBrokerMessageHandler`.
* STOMP client for use over TCP and WebSocket; see <<websocket-stomp-client>>.
* `@SendTo` and `@SendToUser` can contain destination variable placeholders.
* Jackson's `@JsonView` supported for return values on `@MessageMapping` and `@SubscribeMapping` methods.
* `ListenableFuture` and `CompletableFuture` as return value types from
  `@MessageMapping` and `@SubscribeMapping` methods.
* `MarshallingMessageConverter` for XML payloads.

=== Testing Improvements

* JUnit-based integration tests can now be executed with JUnit rules
  instead of the `SpringJUnit4ClassRunner`. This allows Spring-based
  integration tests to be run with alternative runners like JUnit's
  `Parameterized` or third-party runners such as the 
  `MockitoJUnitRunner`.
** Spring JUnit rule configuration requires the following two rules.
[source,java,indent=0]
[subs="verbatim,quotes"]
----
    @ClassRule
    public static final SpringClassRule SPRING_CLASS_RULE = new SpringClassRule();

    @Rule
    public final SpringMethodRule springMethodRule = new SpringMethodRule();
----
* The `ContextCache` that is used for caching ++ApplicationContext++s
  between tests is now a public API with a default implementation that
  can be replaced for custom caching needs.
* `DefaultTestContext`, `DefaultBootstrapContext`, and
  `DefaultCacheAwareContextLoaderDelegate` are now public classes in the
  `support` subpackage, allowing for custom extensions.
* ++TestContextBootstrapper++s are now responsible for building the
  `TestContext`.
* `ReflectionTestUtils` now supports setting and getting `static` fields,
  including constants.
* `@DirtiesContext` supports new `BEFORE_METHOD`, `BEFORE_CLASS`, and
  `BEFORE_EACH_TEST_METHOD` modes for closing the `ApplicationContext`
  _before_ a test -- for example, if some rogue (i.e., yet to be
  determined) test within a large test suite has corrupted the original
  configuration for the `ApplicationContext`.
* The JDBC XML namespace supports a new `database-name` attribute in
  `<jdbc:embedded-database>`, allowing developers to set unique names
  for embedded databases –- for example, via a SpEL expression or a
  property placeholder that is influenced by the current active bean
  definition profiles.
* Embedded databases can now be automatically assigned a unique name,
  allowing common test database configuration to be reused in different
  ++ApplicationContext++s within a test suite. This support can be enabled
  via:
** `EmbeddedDatabaseFactory.setGenerateUniqueDatabaseName()`
** `EmbeddedDatabaseBuilder.generateUniqueName()`
** `<jdbc:embedded-database generate-name="true" ... >`
* `AopTestUtils` is a new testing utility that allows developers to
  obtain a reference to the underlying target object hidden behind one
  or more Spring proxies.