Improve @EventListener documentation

spring-context/src/main/java/org/springframework/context/event/EventListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,18 +48,39 @@ import org.springframework.core.annotation.AliasFor;
  * return type is either an array or a collection, each element is sent
  * as a new individual event.
  *
+ * <p>This annotation may be used as a <em>meta-annotation</em> to create custom
+ * <em>composed annotations</em>.
+ *
+ * <h3>Exception Handling</h3>
+ * <p>While it is possible for an event listener to declare that it
+ * throws arbitrary exception types, any checked exceptions thrown
+ * from an event listener will be wrapped in an
+ * {@link java.lang.reflect.UndeclaredThrowableException UndeclaredThrowableException}
+ * since the event publisher can only handle runtime exceptions.
+ *
+ * <h3>Asynchronous Listeners</h3>
+ * <p>If you want a particular listener to process events asynchronously, you
+ * can use Spring's {@link org.springframework.scheduling.annotation.Async @Async}
+ * support, but be aware of the following limitations when using asynchronous events.
+ *
+ * <ul>
+ * <li>If an asynchronous event listener throws an exception, it is not propagated
+ * to the caller. See {@link org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler
+ * AsyncUncaughtExceptionHandler} for more details.</li>
+ * <li>Asynchronous event listener methods cannot publish a subsequent event by returning a
+ * value. If you need to publish another event as the result of the processing, inject an
+ * {@link org.springframework.context.ApplicationEventPublisher ApplicationEventPublisher}
+ * to publish the event manually.</li>
+ * </ul>
+ *
+ * <h3>Ordering Listeners</h3>
  * <p>It is also possible to define the order in which listeners for a
  * certain event are to be invoked. To do so, add Spring's common
  * {@link org.springframework.core.annotation.Order @Order} annotation
  * alongside this event listener annotation.
  *
- * <p>While it is possible for an event listener to declare that it
- * throws arbitrary exception types, any checked exceptions thrown
- * from an event listener will be wrapped in an
- * {@link java.lang.reflect.UndeclaredThrowableException}
- * since the event publisher can only handle runtime exceptions.
- *
  * @author Stephane Nicoll
+ * @author Sam Brannen
  * @since 4.2
  * @see EventListenerMethodProcessor
  */
@@ -91,13 +112,15 @@ public @interface EventListener {
 	 * <p>The SpEL expression evaluates against a dedicated context that
 	 * provides the following meta-data:
 	 * <ul>
-	 * <li>{@code #root.event}, {@code #root.args} for
+	 * <li>{@code #root.event} or {@code event} for references to the
-	 * references to the {@link ApplicationEvent} and method arguments
+	 * {@link ApplicationEvent}</li>
-	 * respectively.</li>
+	 * <li>{@code #root.args} or {@code args} for references to the method
+	 * arguments array</li>
 	 * <li>Method arguments can be accessed by index. For instance the
-	 * first argument can be accessed via {@code #root.args[0]}, {@code #p0}
+	 * first argument can be accessed via {@code #root.args[0]}, {@code args[0]},
-	 * or {@code #a0}. Arguments can also be accessed by name if that
+	 * {@code #a0}, or {@code #p0}. Arguments can also be accessed by name (with
-	 * information is available.</li>
+	 * a preceding hash tag) if that information is available in the compiled
+	 * byte code.</li>
 	 * </ul>
 	 */
 	String condition() default "";

src/docs/asciidoc/core/core-beans.adoc

@@ -8463,6 +8463,10 @@ The following table describes the standard events that Spring provides:
 | 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`.
+
+| `ServletRequestHandledEvent`
+| A subclass of `RequestHandledEvent` that adds Servlet-specific context information.
+
 |===
 
 You can also create and publish your own custom events. The following example shows a
@@ -8552,8 +8556,10 @@ synchronously. This means that the `publishEvent()` method blocks until all list
 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, See the javadoc for Spring's
+event publication becomes necessary, see the javadoc for Spring's
-{api-spring-framework}/context/event/ApplicationEventMulticaster.html[`ApplicationEventMulticaster`] interface.
+{api-spring-framework}/context/event/ApplicationEventMulticaster.html[`ApplicationEventMulticaster`] interface
+and {api-spring-framework}/context/event/SimpleApplicationEventMulticaster.html[`SimpleApplicationEventMulticaster`]
+implementation for configuration options.
 
 The following example shows the bean definitions used to register and configure each of
 the classes above:
@@ -8595,7 +8601,7 @@ architectures that build upon the well-known Spring programming model.
 ==== Annotation-based Event Listeners
 
 As of Spring 4.2, you can register an event listener on any public method of a managed
-bean by using the `EventListener` annotation. The `BlackListNotifier` can be rewritten as
+bean by using the `@EventListener` annotation. The `BlackListNotifier` can be rewritten as
 follows:
 
 [source,java,indent=0]
@@ -8661,19 +8667,20 @@ items made available to the context so that you can use them for conditional eve
 | Event
 | root object
 | The actual `ApplicationEvent`.
-| `#root.event`
+| `#root.event` or `event`
 
 | Arguments array
 | root object
-| The arguments (as array) used for invoking the target.
+| The arguments (as an object array) used to invoke the method.
-| `#root.args[0]`
+| `#root.args` or `args`; `args[0]` to access the first argument, etc.
 
 | __Argument name__
 | evaluation context
 | The name of any of the method arguments. If, for some reason, the names are not available
-  (for example, because there is no debug information), the argument names are also available under the `#a<#arg>`
+  (for example, because there is no debug information in the compiled byte code), individual
-  where `#arg` stands for the argument index (starting from 0).
+  arguments are also available using the `#a<#arg>` syntax where `<#arg>` stands for the
-| `#blEvent` or `#a0` (you can also use `#p0` or `#p<#arg>` notation as an alias)
+  argument index (starting from 0).
+| `#blEvent` or `#a0` (you can also use `#p0` or `#p<#arg>` parameter notation as an alias)
 |===
 
 Note that `#root.event` gives you access to the underlying event, even if your method
@@ -8719,11 +8726,12 @@ following example shows how to do so:
 
 Be aware of the following limitations when using asynchronous events:
 
-* If the event listener throws an `Exception`, it is not propagated to the caller
+* If an asynchronous event listener throws an `Exception`, it is not propagated to the
-  See `AsyncUncaughtExceptionHandler` for more details.
+  caller. See `AsyncUncaughtExceptionHandler` for more details.
-* Such event listener cannot send replies. If you need to send another event as the
+* Asynchronous event listener methods cannot publish a subsequent event by returning a
-  result of the processing, inject {api-spring-framework}/aop/interceptor/AsyncUncaughtExceptionHandler.html[`ApplicationEventPublisher`] to send the event
+  value. If you need to publish another event as the result of the processing, inject an
-  manually.
+  {api-spring-framework}/aop/interceptor/AsyncUncaughtExceptionHandler.html[`ApplicationEventPublisher`]
+  to publish the event manually.
 
 
 [[context-functionality-events-order]]