As discussed in the chapter introduction, the org.springframework.beans.factory package provides basic functionality for managing and manipulating beans, including in a programmatic way. The org.springframework.context package adds the ApplicationContext interface, which extends the BeanFactory interface, in addition to extending other interfaces to provide additional functionality in a more application framework-oriented style. Many people use the ApplicationContext in a completely declarative fashion, not even creating it programmatically, but instead relying on support classes such as ContextLoader to automatically instantiate an ApplicationContext as part of the normal startup process of a Jakarta EE web application.spring-doc.cn

To enhance BeanFactory functionality in a more framework-oriented style, the context package also provides the following functionality:spring-doc.cn

  • Access to messages in i18n-style, through the MessageSource interface.spring-doc.cn

  • Access to resources, such as URLs and files, through the ResourceLoader interface.spring-doc.cn

  • Event publication, namely to beans that implement the ApplicationListener interface, through the use of the ApplicationEventPublisher interface.spring-doc.cn

  • Loading of multiple (hierarchical) contexts, letting each be focused on one particular layer, such as the web layer of an application, through the HierarchicalBeanFactory interface.spring-doc.cn

Internationalization using MessageSource

The ApplicationContext interface extends an interface called MessageSource and, therefore, provides internationalization (“i18n”) functionality. Spring also provides the HierarchicalMessageSource interface, which can resolve messages hierarchically. Together, these interfaces provide the foundation upon which Spring effects message resolution. The methods defined on these interfaces include:spring-doc.cn

  • String getMessage(String code, Object[] args, String default, Locale loc): The basic method used to retrieve a message from the MessageSource. When no message is found for the specified locale, the default message is used. Any arguments passed in become replacement values, using the MessageFormat functionality provided by the standard library.spring-doc.cn

  • String getMessage(String code, Object[] args, Locale loc): Essentially the same as the previous method but with one difference: No default message can be specified. If the message cannot be found, a NoSuchMessageException is thrown.spring-doc.cn

  • String getMessage(MessageSourceResolvable resolvable, Locale locale): All properties used in the preceding methods are also wrapped in a class named MessageSourceResolvable, which you can use with this method.spring-doc.cn

When an ApplicationContext is loaded, it automatically searches for a MessageSource bean defined in the context. The bean must have the name messageSource. If such a bean is found, all calls to the preceding methods are delegated to the message source. If no message source is found, the ApplicationContext attempts to find a parent containing a bean with the same name. If it does, it uses that bean as the MessageSource. If the ApplicationContext cannot find any source for messages, an empty DelegatingMessageSource is instantiated in order to be able to accept calls to the methods defined above.spring-doc.cn

Spring provides three MessageSource implementations, ResourceBundleMessageSource, ReloadableResourceBundleMessageSource and StaticMessageSource. All of them implement HierarchicalMessageSource in order to do nested messaging. The StaticMessageSource is rarely used but provides programmatic ways to add messages to the source. The following example shows ResourceBundleMessageSource:spring-doc.cn

<beans>
	<bean id="messageSource"
			class="org.springframework.context.support.ResourceBundleMessageSource">
		<property name="basenames">
			<list>
				<value>format</value>
				<value>exceptions</value>
				<value>windows</value>
			</list>
		</property>
	</bean>
</beans>

The example assumes that you have three resource bundles called format, exceptions and windows defined in your classpath. Any request to resolve a message is handled in the JDK-standard way of resolving messages through ResourceBundle objects. For the purposes of the example, assume the contents of two of the above resource bundle files are as follows:spring-doc.cn

# in format.properties
message=Alligators rock!
# in exceptions.properties
argument.required=The {0} argument is required.

The next example shows a program to run the MessageSource functionality. Remember that all ApplicationContext implementations are also MessageSource implementations and so can be cast to the MessageSource interface.spring-doc.cn

public static void main(String[] args) {
	MessageSource resources = new ClassPathXmlApplicationContext("beans.xml");
	String message = resources.getMessage("message", null, "Default", Locale.ENGLISH);
	System.out.println(message);
}
fun main() {
	val resources = ClassPathXmlApplicationContext("beans.xml")
	val message = resources.getMessage("message", null, "Default", Locale.ENGLISH)
	println(message)
}

The resulting output from the above program is as follows:spring-doc.cn

Alligators rock!

To summarize, the MessageSource is defined in a file called beans.xml, which exists at the root of your classpath. The messageSource bean definition refers to a number of resource bundles through its basenames property. The three files that are passed in the list to the basenames property exist as files at the root of your classpath and are called format.properties, exceptions.properties, and windows.properties, respectively.spring-doc.cn

The next example shows arguments passed to the message lookup. These arguments are converted into String objects and inserted into placeholders in the lookup message.spring-doc.cn

<beans>

	<!-- this MessageSource is being used in a web application -->
	<bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource">
		<property name="basename" value="exceptions"/>
	</bean>

	<!-- lets inject the above MessageSource into this POJO -->
	<bean id="example" class="com.something.Example">
		<property name="messages" ref="messageSource"/>
	</bean>

</beans>
public class Example {

	private MessageSource messages;

	public void setMessages(MessageSource messages) {
		this.messages = messages;
	}

	public void execute() {
		String message = this.messages.getMessage("argument.required",
			new Object [] {"userDao"}, "Required", Locale.ENGLISH);
		System.out.println(message);
	}
}
	class Example {

	lateinit var messages: MessageSource

	fun execute() {
		val message = messages.getMessage("argument.required",
				arrayOf("userDao"), "Required", Locale.ENGLISH)
		println(message)
	}
}

The resulting output from the invocation of the execute() method is as follows:spring-doc.cn

The userDao argument is required.

With regard to internationalization (“i18n”), Spring’s various MessageSource implementations follow the same locale resolution and fallback rules as the standard JDK ResourceBundle. In short, and continuing with the example messageSource defined previously, if you want to resolve messages against the British (en-GB) locale, you would create files called format_en_GB.properties, exceptions_en_GB.properties, and windows_en_GB.properties, respectively.spring-doc.cn

Typically, locale resolution is managed by the surrounding environment of the application. In the following example, the locale against which (British) messages are resolved is specified manually:spring-doc.cn

# in exceptions_en_GB.properties
argument.required=Ebagum lad, the ''{0}'' argument is required, I say, required.
public static void main(final String[] args) {
	MessageSource resources = new ClassPathXmlApplicationContext("beans.xml");
	String message = resources.getMessage("argument.required",
		new Object [] {"userDao"}, "Required", Locale.UK);
	System.out.println(message);
}
fun main() {
	val resources = ClassPathXmlApplicationContext("beans.xml")
	val message = resources.getMessage("argument.required",
			arrayOf("userDao"), "Required", Locale.UK)
	println(message)
}

The resulting output from the running of the above program is as follows:spring-doc.cn

Ebagum lad, the 'userDao' argument is required, I say, required.

You can also use the MessageSourceAware interface to acquire a reference to any MessageSource that has been defined. Any bean that is defined in an ApplicationContext that implements the MessageSourceAware interface is injected with the application context’s MessageSource when the bean is created and configured.spring-doc.cn

Because Spring’s MessageSource is based on Java’s ResourceBundle, it does not merge bundles with the same base name, but will only use the first bundle found. Subsequent message bundles with the same base name are ignored.
As an alternative to ResourceBundleMessageSource, Spring provides a ReloadableResourceBundleMessageSource class. This variant supports the same bundle file format but is more flexible than the standard JDK based ResourceBundleMessageSource implementation. In particular, it allows for reading files from any Spring resource location (not only from the classpath) and supports hot reloading of bundle property files (while efficiently caching them in between). See the ReloadableResourceBundleMessageSource javadoc for details.
Because Spring’s MessageSource is based on Java’s ResourceBundle, it does not merge bundles with the same base name, but will only use the first bundle found. Subsequent message bundles with the same base name are ignored.
As an alternative to ResourceBundleMessageSource, Spring provides a ReloadableResourceBundleMessageSource class. This variant supports the same bundle file format but is more flexible than the standard JDK based ResourceBundleMessageSource implementation. In particular, it allows for reading files from any Spring resource location (not only from the classpath) and supports hot reloading of bundle property files (while efficiently caching them in between). See the ReloadableResourceBundleMessageSource javadoc for details.

Standard and Custom Events

Event handling in the ApplicationContext is provided through the ApplicationEvent class and the ApplicationListener interface. If a bean that implements the ApplicationListener interface is deployed into the context, every time an ApplicationEvent gets published to the ApplicationContext, that bean is notified. Essentially, this is the standard Observer design pattern.spring-doc.cn

As of Spring 4.2, the event infrastructure has been significantly improved and offers an annotation-based model as well as the ability to publish any arbitrary event (that is, an object that does not necessarily extend from ApplicationEvent). When such an object is published, we wrap it in an event for you.

The following table describes the standard events that Spring provides:spring-doc.cn

Table 1. Built-in Events
Event Explanation

ContextRefreshedEventspring-doc.cn

Published when the ApplicationContext is initialized or refreshed (for example, by using the refresh() method on the ConfigurableApplicationContext interface). Here, “initialized” means that all beans are loaded, post-processor beans are detected and activated, singletons are pre-instantiated, and the ApplicationContext object is ready for use. As long as the context has not been closed, a refresh can be triggered multiple times, provided that the chosen ApplicationContext actually supports such “hot” refreshes. For example, XmlWebApplicationContext supports hot refreshes, but GenericApplicationContext does not.spring-doc.cn

ContextStartedEventspring-doc.cn

Published when the ApplicationContext is started by using the start() method on the ConfigurableApplicationContext interface. Here, “started” means that all Lifecycle beans receive an explicit start signal. Typically, this signal is used to restart beans after an explicit stop, but it may also be used to start components that have not been configured for autostart (for example, components that have not already started on initialization).spring-doc.cn

ContextStoppedEventspring-doc.cn

Published when the ApplicationContext is stopped by using the stop() method on the ConfigurableApplicationContext interface. Here, “stopped” means that all Lifecycle beans receive an explicit stop signal. A stopped context may be restarted through a start() call.spring-doc.cn

ContextClosedEventspring-doc.cn

Published when the ApplicationContext is being closed by using the close() method on the ConfigurableApplicationContext interface or via a JVM shutdown hook. Here, "closed" means that all singleton beans will be destroyed. Once the context is closed, it reaches its end of life and cannot be refreshed or restarted.spring-doc.cn

RequestHandledEventspring-doc.cn

A web-specific event telling all beans that an HTTP request has been serviced. This event is published after the request is complete. This event is only applicable to web applications that use Spring’s DispatcherServlet.spring-doc.cn

ServletRequestHandledEventspring-doc.cn

A subclass of RequestHandledEvent that adds Servlet-specific context information.spring-doc.cn

You can also create and publish your own custom events. The following example shows a simple class that extends Spring’s ApplicationEvent base class:spring-doc.cn

public class BlockedListEvent extends ApplicationEvent {

	private final String address;
	private final String content;

	public BlockedListEvent(Object source, String address, String content) {
		super(source);
		this.address = address;
		this.content = content;
	}

	// accessor and other methods...
}
class BlockedListEvent(source: Any,
					val address: String,
					val content: String) : ApplicationEvent(source)

To publish a custom ApplicationEvent, call the publishEvent() method on an ApplicationEventPublisher. Typically, this is done by creating a class that implements ApplicationEventPublisherAware and registering it as a Spring bean. The following example shows such a class:spring-doc.cn

public class EmailService implements ApplicationEventPublisherAware {

	private List<String> blockedList;
	private ApplicationEventPublisher publisher;

	public void setBlockedList(List<String> blockedList) {
		this.blockedList = blockedList;
	}

	public void setApplicationEventPublisher(ApplicationEventPublisher publisher) {
		this.publisher = publisher;
	}

	public void sendEmail(String address, String content) {
		if (blockedList.contains(address)) {
			publisher.publishEvent(new BlockedListEvent(this, address, content));
			return;
		}
		// send email...
	}
}
class EmailService : ApplicationEventPublisherAware {

	private lateinit var blockedList: List<String>
	private lateinit var publisher: ApplicationEventPublisher

	fun setBlockedList(blockedList: List<String>) {
		this.blockedList = blockedList
	}

	override fun setApplicationEventPublisher(publisher: ApplicationEventPublisher) {
		this.publisher = publisher
	}

	fun sendEmail(address: String, content: String) {
		if (blockedList!!.contains(address)) {
			publisher!!.publishEvent(BlockedListEvent(this, address, content))
			return
		}
		// send email...
	}
}

At configuration time, the Spring container detects that EmailService implements ApplicationEventPublisherAware and automatically calls setApplicationEventPublisher(). In reality, the parameter passed in is the Spring container itself. You are interacting with the application context through its ApplicationEventPublisher interface.spring-doc.cn

To receive the custom ApplicationEvent, you can create a class that implements ApplicationListener and register it as a Spring bean. The following example shows such a class:spring-doc.cn

public class BlockedListNotifier implements ApplicationListener<BlockedListEvent> {

	private String notificationAddress;

	public void setNotificationAddress(String notificationAddress) {
		this.notificationAddress = notificationAddress;
	}

	public void onApplicationEvent(BlockedListEvent event) {
		// notify appropriate parties via notificationAddress...
	}
}
class BlockedListNotifier : ApplicationListener<BlockedListEvent> {

	lateinit var notificationAddress: String

	override fun onApplicationEvent(event: BlockedListEvent) {
		// notify appropriate parties via notificationAddress...
	}
}

Notice that ApplicationListener is generically parameterized with the type of your custom event (BlockedListEvent in the preceding example). This means that the onApplicationEvent() method can remain type-safe, avoiding any need for downcasting. You can register as many event listeners as you wish, but note that, by default, event listeners receive events synchronously. This means that the publishEvent() method blocks until all listeners have finished processing the event. One advantage of this synchronous and single-threaded approach is that, when a listener receives an event, it operates inside the transaction context of the publisher if a transaction context is available. If another strategy for event publication becomes necessary, e.g. asynchronous event processing by default, see the javadoc for Spring’s ApplicationEventMulticaster interface and SimpleApplicationEventMulticaster implementation for configuration options which can be applied to a custom "applicationEventMulticaster" bean definition. In these cases, ThreadLocals and logging context are not propagated for the event processing. See the @EventListener Observability section for more information on Observability concerns.spring-doc.cn

The following example shows the bean definitions used to register and configure each of the classes above:spring-doc.cn

<bean id="emailService" class="example.EmailService">
	<property name="blockedList">
		<list>
			<value>[email protected]</value>
			<value>[email protected]</value>
			<value>[email protected]</value>
		</list>
	</property>
</bean>

<bean id="blockedListNotifier" class="example.BlockedListNotifier">
	<property name="notificationAddress" value="[email protected]"/>
</bean>

   <!-- optional: a custom ApplicationEventMulticaster definition -->
<bean id="applicationEventMulticaster" class="org.springframework.context.event.SimpleApplicationEventMulticaster">
	<property name="taskExecutor" ref="..."/>
	<property name="errorHandler" ref="..."/>
</bean>

Putting it all together, when the sendEmail() method of the emailService bean is called, if there are any email messages that should be blocked, a custom event of type BlockedListEvent is published. The blockedListNotifier bean is registered as an ApplicationListener and receives the BlockedListEvent, at which point it can notify appropriate parties.spring-doc.cn

Spring’s eventing mechanism is designed for simple communication between Spring beans within the same application context. However, for more sophisticated enterprise integration needs, the separately maintained Spring Integration project provides complete support for building lightweight, pattern-oriented, event-driven architectures that build upon the well-known Spring programming model.

Annotation-based Event Listeners

You can register an event listener on any method of a managed bean by using the @EventListener annotation. The BlockedListNotifier can be rewritten as follows:spring-doc.cn

public class BlockedListNotifier {

	private String notificationAddress;

	public void setNotificationAddress(String notificationAddress) {
		this.notificationAddress = notificationAddress;
	}

	@EventListener
	public void processBlockedListEvent(BlockedListEvent event) {
		// notify appropriate parties via notificationAddress...
	}
}
class BlockedListNotifier {

	lateinit var notificationAddress: String

	@EventListener
	fun processBlockedListEvent(event: BlockedListEvent) {
		// notify appropriate parties via notificationAddress...
	}
}

The method signature once again declares the event type to which it listens, but, this time, with a flexible name and without implementing a specific listener interface. The event type can also be narrowed through generics as long as the actual event type resolves your generic parameter in its implementation hierarchy.spring-doc.cn

If your method should listen to several events or if you want to define it with no parameter at all, the event types can also be specified on the annotation itself. The following example shows how to do so:spring-doc.cn

@EventListener({ContextStartedEvent.class, ContextRefreshedEvent.class})
public void handleContextStart() {
	// ...
}
@EventListener(ContextStartedEvent::class, ContextRefreshedEvent::class)
fun handleContextStart() {
	// ...
}

It is also possible to add additional runtime filtering by using the condition attribute of the annotation that defines a SpEL expression, which should match to actually invoke the method for a particular event.spring-doc.cn

The following example shows how our notifier can be rewritten to be invoked only if the content attribute of the event is equal to my-event:spring-doc.cn

@EventListener(condition = "#blEvent.content == 'my-event'")
public void processBlockedListEvent(BlockedListEvent blEvent) {
	// notify appropriate parties via notificationAddress...
}
@EventListener(condition = "#blEvent.content == 'my-event'")
fun processBlockedListEvent(blEvent: BlockedListEvent) {
	// notify appropriate parties via notificationAddress...
}

Each SpEL expression evaluates against a dedicated context. The following table lists the items made available to the context so that you can use them for conditional event processing:spring-doc.cn

Table 2. Event metadata available in SpEL expressions
Name Location Description Example

Eventspring-doc.cn

root objectspring-doc.cn

The actual ApplicationEvent.spring-doc.cn

#root.event or eventspring-doc.cn

Arguments arrayspring-doc.cn

root objectspring-doc.cn

The arguments (as an object array) used to invoke the method.spring-doc.cn

#root.args or args; args[0] to access the first argument, etc.spring-doc.cn

Argument namespring-doc.cn

evaluation contextspring-doc.cn

The name of a particular method argument. If the names are not available (for example, because the code was compiled without the -parameters flag), individual arguments are also available using the #a<#arg> syntax where <#arg> stands for the argument index (starting from 0).spring-doc.cn

#blEvent or #a0 (you can also use #p0 or #p<#arg> parameter notation as an alias)spring-doc.cn

Note that #root.event gives you access to the underlying event, even if your method signature actually refers to an arbitrary object that was published.spring-doc.cn

If you need to publish an event as the result of processing another event, you can change the method signature to return the event that should be published, as the following example shows:spring-doc.cn

@EventListener
public ListUpdateEvent handleBlockedListEvent(BlockedListEvent event) {
	// notify appropriate parties via notificationAddress and
	// then publish a ListUpdateEvent...
}
@EventListener
fun handleBlockedListEvent(event: BlockedListEvent): ListUpdateEvent {
	// notify appropriate parties via notificationAddress and
	// then publish a ListUpdateEvent...
}
This feature is not supported for asynchronous listeners.

The handleBlockedListEvent() method publishes a new ListUpdateEvent for every BlockedListEvent that it handles. If you need to publish several events, you can return a Collection or an array of events instead.spring-doc.cn

Asynchronous Listeners

If you want a particular listener to process events asynchronously, you can reuse the regular @Async support. The following example shows how to do so:spring-doc.cn

@EventListener
@Async
public void processBlockedListEvent(BlockedListEvent event) {
	// BlockedListEvent is processed in a separate thread
}
@EventListener
@Async
fun processBlockedListEvent(event: BlockedListEvent) {
	// BlockedListEvent is processed in a separate thread
}

Be aware of the following limitations when using asynchronous events:spring-doc.cn

Ordering Listeners

If you need one listener to be invoked before another one, you can add the @Order annotation to the method declaration, as the following example shows:spring-doc.cn

@EventListener
@Order(42)
public void processBlockedListEvent(BlockedListEvent event) {
	// notify appropriate parties via notificationAddress...
}
@EventListener
@Order(42)
fun processBlockedListEvent(event: BlockedListEvent) {
	// notify appropriate parties via notificationAddress...
}

Generic Events

You can also use generics to further define the structure of your event. Consider using an EntityCreatedEvent<T> where T is the type of the actual entity that got created. For example, you can create the following listener definition to receive only EntityCreatedEvent for a Person:spring-doc.cn

@EventListener
public void onPersonCreated(EntityCreatedEvent<Person> event) {
	// ...
}
@EventListener
fun onPersonCreated(event: EntityCreatedEvent<Person>) {
	// ...
}

Due to type erasure, this works only if the event that is fired resolves the generic parameters on which the event listener filters (that is, something like class PersonCreatedEvent extends EntityCreatedEvent<Person> { …​ }).spring-doc.cn

In certain circumstances, this may become quite tedious if all events follow the same structure (as should be the case for the event in the preceding example). In such a case, you can implement ResolvableTypeProvider to guide the framework beyond what the runtime environment provides. The following event shows how to do so:spring-doc.cn

public class EntityCreatedEvent<T> extends ApplicationEvent implements ResolvableTypeProvider {

	public EntityCreatedEvent(T entity) {
		super(entity);
	}

	@Override
	public ResolvableType getResolvableType() {
		return ResolvableType.forClassWithGenerics(getClass(), ResolvableType.forInstance(getSource()));
	}
}
class EntityCreatedEvent<T>(entity: T) : ApplicationEvent(entity), ResolvableTypeProvider {

	override fun getResolvableType(): ResolvableType? {
		return ResolvableType.forClassWithGenerics(javaClass, ResolvableType.forInstance(getSource()))
	}
}
This works not only for ApplicationEvent but any arbitrary object that you send as an event.

Finally, as with classic ApplicationListener implementations, the actual multicasting happens via a context-wide ApplicationEventMulticaster at runtime. By default, this is a SimpleApplicationEventMulticaster with synchronous event publication in the caller thread. This can be replaced/customized through an "applicationEventMulticaster" bean definition, e.g. for processing all events asynchronously and/or for handling listener exceptions:spring-doc.cn

@Bean
ApplicationEventMulticaster applicationEventMulticaster() {
	SimpleApplicationEventMulticaster multicaster = new SimpleApplicationEventMulticaster();
	multicaster.setTaskExecutor(...);
	multicaster.setErrorHandler(...);
	return multicaster;
}
As of Spring 4.2, the event infrastructure has been significantly improved and offers an annotation-based model as well as the ability to publish any arbitrary event (that is, an object that does not necessarily extend from ApplicationEvent). When such an object is published, we wrap it in an event for you.
Table 1. Built-in Events
Event Explanation

ContextRefreshedEventspring-doc.cn

Published when the ApplicationContext is initialized or refreshed (for example, by using the refresh() method on the ConfigurableApplicationContext interface). Here, “initialized” means that all beans are loaded, post-processor beans are detected and activated, singletons are pre-instantiated, and the ApplicationContext object is ready for use. As long as the context has not been closed, a refresh can be triggered multiple times, provided that the chosen ApplicationContext actually supports such “hot” refreshes. For example, XmlWebApplicationContext supports hot refreshes, but GenericApplicationContext does not.spring-doc.cn

ContextStartedEventspring-doc.cn

Published when the ApplicationContext is started by using the start() method on the ConfigurableApplicationContext interface. Here, “started” means that all Lifecycle beans receive an explicit start signal. Typically, this signal is used to restart beans after an explicit stop, but it may also be used to start components that have not been configured for autostart (for example, components that have not already started on initialization).spring-doc.cn

ContextStoppedEventspring-doc.cn

Published when the ApplicationContext is stopped by using the stop() method on the ConfigurableApplicationContext interface. Here, “stopped” means that all Lifecycle beans receive an explicit stop signal. A stopped context may be restarted through a start() call.spring-doc.cn

ContextClosedEventspring-doc.cn

Published when the ApplicationContext is being closed by using the close() method on the ConfigurableApplicationContext interface or via a JVM shutdown hook. Here, "closed" means that all singleton beans will be destroyed. Once the context is closed, it reaches its end of life and cannot be refreshed or restarted.spring-doc.cn

RequestHandledEventspring-doc.cn

A web-specific event telling all beans that an HTTP request has been serviced. This event is published after the request is complete. This event is only applicable to web applications that use Spring’s DispatcherServlet.spring-doc.cn

ServletRequestHandledEventspring-doc.cn

A subclass of RequestHandledEvent that adds Servlet-specific context information.spring-doc.cn
Spring’s eventing mechanism is designed for simple communication between Spring beans within the same application context. However, for more sophisticated enterprise integration needs, the separately maintained Spring Integration project provides complete support for building lightweight, pattern-oriented, event-driven architectures that build upon the well-known Spring programming model.
Table 2. Event metadata available in SpEL expressions
Name Location Description Example

Eventspring-doc.cn

root objectspring-doc.cn

The actual ApplicationEvent.spring-doc.cn

#root.event or eventspring-doc.cn

Arguments arrayspring-doc.cn

root objectspring-doc.cn

The arguments (as an object array) used to invoke the method.spring-doc.cn

#root.args or args; args[0] to access the first argument, etc.spring-doc.cn

Argument namespring-doc.cn

evaluation contextspring-doc.cn

The name of a particular method argument. If the names are not available (for example, because the code was compiled without the -parameters flag), individual arguments are also available using the #a<#arg> syntax where <#arg> stands for the argument index (starting from 0).spring-doc.cn

#blEvent or #a0 (you can also use #p0 or #p<#arg> parameter notation as an alias)spring-doc.cn
This feature is not supported for asynchronous listeners.
This works not only for ApplicationEvent but any arbitrary object that you send as an event.

Convenient Access to Low-level Resources

For optimal usage and understanding of application contexts, you should familiarize yourself with Spring’s Resource abstraction, as described in Resources.spring-doc.cn

An application context is a ResourceLoader, which can be used to load Resource objects. A Resource is essentially a more feature rich version of the JDK java.net.URL class. In fact, the implementations of the Resource wrap an instance of java.net.URL, where appropriate. A Resource can obtain low-level resources from almost any location in a transparent fashion, including from the classpath, a filesystem location, anywhere describable with a standard URL, and some other variations. If the resource location string is a simple path without any special prefixes, where those resources come from is specific and appropriate to the actual application context type.spring-doc.cn

You can configure a bean deployed into the application context to implement the special callback interface, ResourceLoaderAware, to be automatically called back at initialization time with the application context itself passed in as the ResourceLoader. You can also expose properties of type Resource, to be used to access static resources. They are injected into it like any other properties. You can specify those Resource properties as simple String paths and rely on automatic conversion from those text strings to actual Resource objects when the bean is deployed.spring-doc.cn

The location path or paths supplied to an ApplicationContext constructor are actually resource strings and, in simple form, are treated appropriately according to the specific context implementation. For example ClassPathXmlApplicationContext treats a simple location path as a classpath location. You can also use location paths (resource strings) with special prefixes to force loading of definitions from the classpath or a URL, regardless of the actual context type.spring-doc.cn

Application Startup Tracking

The ApplicationContext manages the lifecycle of Spring applications and provides a rich programming model around components. As a result, complex applications can have equally complex component graphs and startup phases.spring-doc.cn

Tracking the application startup steps with specific metrics can help understand where time is being spent during the startup phase, but it can also be used as a way to better understand the context lifecycle as a whole.spring-doc.cn

The AbstractApplicationContext (and its subclasses) is instrumented with an ApplicationStartup, which collects StartupStep data about various startup phases:spring-doc.cn

  • application context lifecycle (base packages scanning, config classes management)spring-doc.cn

  • beans lifecycle (instantiation, smart initialization, post processing)spring-doc.cn

  • application events processingspring-doc.cn

Here is an example of instrumentation in the AnnotationConfigApplicationContext:spring-doc.cn

// create a startup step and start recording
StartupStep scanPackages = getApplicationStartup().start("spring.context.base-packages.scan");
// add tagging information to the current step
scanPackages.tag("packages", () -> Arrays.toString(basePackages));
// perform the actual phase we're instrumenting
this.scanner.scan(basePackages);
// end the current step
scanPackages.end();
// create a startup step and start recording
val scanPackages = getApplicationStartup().start("spring.context.base-packages.scan")
// add tagging information to the current step
scanPackages.tag("packages", () -> Arrays.toString(basePackages))
// perform the actual phase we're instrumenting
this.scanner.scan(basePackages)
// end the current step
scanPackages.end()

The application context is already instrumented with multiple steps. Once recorded, these startup steps can be collected, displayed and analyzed with specific tools. For a complete list of existing startup steps, you can check out the dedicated appendix section.spring-doc.cn

The default ApplicationStartup implementation is a no-op variant, for minimal overhead. This means no metrics will be collected during application startup by default. Spring Framework ships with an implementation for tracking startup steps with Java Flight Recorder: FlightRecorderApplicationStartup. To use this variant, you must configure an instance of it to the ApplicationContext as soon as it’s been created.spring-doc.cn

Developers can also use the ApplicationStartup infrastructure if they’re providing their own AbstractApplicationContext subclass, or if they wish to collect more precise data.spring-doc.cn

ApplicationStartup is meant to be only used during application startup and for the core container; this is by no means a replacement for Java profilers or metrics libraries like Micrometer.

To start collecting custom StartupStep, components can either get the ApplicationStartup instance from the application context directly, make their component implement ApplicationStartupAware, or ask for the ApplicationStartup type on any injection point.spring-doc.cn

Developers should not use the "spring.*" namespace when creating custom startup steps. This namespace is reserved for internal Spring usage and is subject to change.
ApplicationStartup is meant to be only used during application startup and for the core container; this is by no means a replacement for Java profilers or metrics libraries like Micrometer.
Developers should not use the "spring.*" namespace when creating custom startup steps. This namespace is reserved for internal Spring usage and is subject to change.

Convenient ApplicationContext Instantiation for Web Applications

You can create ApplicationContext instances declaratively by using, for example, a ContextLoader. Of course, you can also create ApplicationContext instances programmatically by using one of the ApplicationContext implementations.spring-doc.cn

You can register an ApplicationContext by using the ContextLoaderListener, as the following example shows:spring-doc.cn

<context-param>
	<param-name>contextConfigLocation</param-name>
	<param-value>/WEB-INF/daoContext.xml /WEB-INF/applicationContext.xml</param-value>
</context-param>

<listener>
	<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

The listener inspects the contextConfigLocation parameter. If the parameter does not exist, the listener uses /WEB-INF/applicationContext.xml as a default. When the parameter does exist, the listener separates the String by using predefined delimiters (comma, semicolon, and whitespace) and uses the values as locations where application contexts are searched. Ant-style path patterns are supported as well. Examples are /WEB-INF/*Context.xml (for all files with names that end with Context.xml and that reside in the WEB-INF directory) and /WEB-INF/**/*Context.xml (for all such files in any subdirectory of WEB-INF).spring-doc.cn

Deploying a Spring ApplicationContext as a Jakarta EE RAR File

It is possible to deploy a Spring ApplicationContext as a RAR file, encapsulating the context and all of its required bean classes and library JARs in a Jakarta EE RAR deployment unit. This is the equivalent of bootstrapping a stand-alone ApplicationContext (only hosted in Jakarta EE environment) being able to access the Jakarta EE servers facilities. RAR deployment is a more natural alternative to a scenario of deploying a headless WAR file — in effect, a WAR file without any HTTP entry points that is used only for bootstrapping a Spring ApplicationContext in a Jakarta EE environment.spring-doc.cn

RAR deployment is ideal for application contexts that do not need HTTP entry points but rather consist only of message endpoints and scheduled jobs. Beans in such a context can use application server resources such as the JTA transaction manager and JNDI-bound JDBC DataSource instances and JMS ConnectionFactory instances and can also register with the platform’s JMX server — all through Spring’s standard transaction management and JNDI and JMX support facilities. Application components can also interact with the application server’s JCA WorkManager through Spring’s TaskExecutor abstraction.spring-doc.cn

See the javadoc of the SpringContextResourceAdapter class for the configuration details involved in RAR deployment.spring-doc.cn

For a simple deployment of a Spring ApplicationContext as a Jakarta EE RAR file:spring-doc.cn

  1. Package all application classes into a RAR file (which is a standard JAR file with a different file extension).spring-doc.cn

  2. Add all required library JARs into the root of the RAR archive.spring-doc.cn

  3. Add a META-INF/ra.xml deployment descriptor (as shown in the javadoc for SpringContextResourceAdapter) and the corresponding Spring XML bean definition file(s) (typically META-INF/applicationContext.xml).spring-doc.cn

  4. Drop the resulting RAR file into your application server’s deployment directory.spring-doc.cn

Such RAR deployment units are usually self-contained. They do not expose components to the outside world, not even to other modules of the same application. Interaction with a RAR-based ApplicationContext usually occurs through JMS destinations that it shares with other modules. A RAR-based ApplicationContext may also, for example, schedule some jobs or react to new files in the file system (or the like). If it needs to allow synchronous access from the outside, it could (for example) export RMI endpoints, which may be used by other application modules on the same machine.
Such RAR deployment units are usually self-contained. They do not expose components to the outside world, not even to other modules of the same application. Interaction with a RAR-based ApplicationContext usually occurs through JMS destinations that it shares with other modules. A RAR-based ApplicationContext may also, for example, schedule some jobs or react to new files in the file system (or the like). If it needs to allow synchronous access from the outside, it could (for example) export RMI endpoints, which may be used by other application modules on the same machine.