5. New Features and Enhancements in Spring Framework 4.2

5. New Features and Enhancements in Spring Framework 4.2
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5.1 Core Container Improvements

Annotations such as @Bean get detected and processed on Java 8 default methods as well, allowing for composing a configuration class from interfaces with default @Bean methods.
Configuration classes may declare @Import with regular component classes now, allowing for a mix of imported configuration classes and component classes.
Configuration classes may declare an @Order value, getting processed in a corresponding order (e.g. for overriding beans by name) even when detected through classpath scanning.
@Resource injection points support an @Lazy declaration, analogous to @Autowired, receiving a lazy-initializing proxy for the requested target bean.
The application event infrastructure now offers an 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 in order to provide meaningful aliases for their value attributes: @Cacheable, @CacheEvict, @CachePut, @ComponentScan, @ComponentScan.Filter, @ImportResource, @Scope, @ManagedResource, @Header, @Payload, @SendToUser, @ActiveProfiles, @ContextConfiguration, @Sql, @TestExecutionListeners, @TestPropertySource, @Transactional, @ControllerAdvice, @CookieValue, @CrossOrigin, @MatrixVariable, @RequestHeader, @RequestMapping, @RequestParam, @RequestPart, @ResponseStatus, @SessionAttributes, @ActionMapping, @RenderMapping, @EventListener, @TransactionalEventListener.
- For example, @ContextConfiguration from the spring-test module is now declared as follows:
```
public @interface ContextConfiguration {

    @AliasFor("locations")
    String[] value() default {};

    @AliasFor("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.
```
@ContextConfiguration
public @interface MyTestConfig {

    @AliasFor(annotation = ContextConfiguration.class, attribute = "value")
    String[] xmlFiles();

    // ...
}
```
- See Spring Annotation Programming Model.
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.
Maps representing annotation attributes (and AnnotationAttributes instances) can be synthesized (i.e., converted) into an annotation.
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.
DefaultFormattingConversionService comes with out-of-the-box support for the value types in JSR-354 Money & Currency (if the 'javax.money' API is present on the classpath): namely, MonetaryAmount and CurrencyUnit. This includes support for applying @NumberFormat.
@NumberFormat can now be used as a meta-annotation.
JavaMailSenderImpl has a new testConnection() method for checking connectivity to the server.
ScheduledTaskRegistrar exposes scheduled tasks.
Apache commons-pool2 is now supported for a pooling AOP CommonsPool2TargetSource.
Introduced StandardScriptFactory as a JSR-223 based mechanism for scripted beans, exposed through the lang:std element in XML. Supports e.g. JavaScript and JRuby. (Note: JRubyScriptFactory and lang:jruby are deprecated now, in favor of using JSR-223.)

5.2 Data Access Improvements

javax.transaction.Transactional is now supported via AspectJ.
SimpleJdbcCallOperations now supports named binding.
Full support for Hibernate ORM 5.0: as a JPA provider (automatically adapted) as well as through its native API (covered by the new org.springframework.orm.hibernate5 package).
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.

5.3 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.
The response destination can be computed at runtime using JmsResponse
@JmsListener is now a repeatable annotation to declare several JMS containers on the same method (use the newly introduced @JmsListeners if you’re not using Java8 yet).

5.4 Web Improvements

HTTP Streaming and Server-Sent Events support, see the section called “HTTP Streaming”.
Built-in support for CORS including global (MVC Java config and XML namespace) and local (e.g. @CrossOrigin) configuration. See Chapter 27, CORS Support for details.
HTTP caching updates:
- new CacheControl builder; plugged into ResponseEntity, WebContentGenerator, ResourceHttpRequestHandler.
- improved ETag/Last-Modified support in WebRequest.
Custom mapping annotations, using @RequestMapping as a meta-annotation.
Public methods in AbstractHandlerMethodMapping to register and unregister request mappings at runtime.
Protected createDispatcherServlet method in AbstractDispatcherServletInitializer to further customize the DispatcherServlet instance to use.
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.
OkHTTP integration with the RestTemplate.
Custom baseUrl alternative for methods in MvcUriComponentsBuilder.
Serialization/deserialization exception messages are now logged at WARN level.
Default JSON prefix has been changed from "{} && " to the safer ")]}', " one.
New RequestBodyAdvice extension point and built-in implementation to support Jackson’s @JsonView on @RequestBody method arguments.
When using GSON or Jackson 2.6+, the handler method return type is used to improve serialization of parameterized types like List<Foo>.
Introduced ScriptTemplateView as a JSR-223 based mechanism for scripted web views, with a focus on JavaScript view templating on Nashorn (JDK 8).

5.5 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 Section 26.4.13, “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.

5.6 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.
- See the section called “Spring JUnit 4 Rules” for details.
The Spring MVC Test framework now provides first-class support for HtmlUnit, including integration with Selenium’s WebDriver, allowing for page-based web application testing without the need to deploy to a Servlet container.
- See Section 15.6.2, “HtmlUnit Integration” for details.
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.
- See Section 14.2.1, “General testing utilities” for details.
ReflectionTestUtils now supports setting and getting static fields, including constants.
The original ordering of bean definition profiles declared via @ActiveProfiles is now retained in order to support use cases such as Spring Boot’s ConfigFileApplicationListener which loads configuration files based on the names of active profiles.
@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.
@Commit is a new annotation that may be used as a direct replacement for @Rollback(false).
@Rollback may now be used to configure class-level default rollback semantics.
- Consequently, @TransactionConfiguration is now deprecated and will be removed in a subsequent release.
@Sql now supports execution of inlined SQL statements via a new statements attribute.
The ContextCache that is used for caching ApplicationContexts 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.
TestContextBootstrappers are now responsible for building the TestContext.
In the Spring MVC Test framework, MvcResult details can now be logged at DEBUG level or written to a custom OutputStream or Writer. See the new log(), print(OutputStream), and print(Writer) methods in MockMvcResultHandlers for details.
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 ApplicationContexts within a test suite.
- See Section 19.8.6, “Generating unique names for embedded databases” for details.
MockHttpServletRequest and MockHttpServletResponse now provide better support for date header formatting via the getDateHeader and setDateHeader methods.

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