org.springframework.context.event.EventListener Maven / Gradle / Ivy
/*
* Copyright 2002-2016 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.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.context.event;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.ApplicationEvent;
import org.springframework.core.annotation.AliasFor;
/**
* Annotation that marks a method as a listener for application events.
*
* If an annotated method supports a single event type, the method may
* declare a single parameter that reflects the event type to listen to.
* If an annotated method supports multiple event types, this annotation
* may refer to one or more supported event types using the {@code classes}
* attribute. See the {@link #classes} javadoc for further details.
*
*
Events can be {@link ApplicationEvent} instances as well as arbitrary
* objects.
*
*
Processing of {@code @EventListener} annotations is performed via
* the internal {@link EventListenerMethodProcessor} bean which gets
* registered automatically when using Java config or manually via the
* {@code } or {@code }
* element when using XML config.
*
*
Annotated methods may have a non-{@code void} return type. When they
* do, the result of the method invocation is sent as a new event. If the
* return type is either an array or a collection, each element is sent
* as a new individual event.
*
*
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.
*
*
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
* @since 4.2
* @see EventListenerMethodProcessor
*/
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EventListener {
/**
* Alias for {@link #classes}.
*/
@AliasFor("classes")
Class[] value() default {};
/**
* The event classes that this listener handles.
*
If this attribute is specified with a single value, the
* annotated method may optionally accept a single parameter.
* However, if this attribute is specified with multiple values,
* the annotated method must not declare any parameters.
*/
@AliasFor("value")
Class[] classes() default {};
/**
* Spring Expression Language (SpEL) attribute used for making the
* event handling conditional.
*
Default is {@code ""}, meaning the event is always handled.
*
The SpEL expression evaluates against a dedicated context that
* provides the following meta-data:
*
* - {@code #root.event}, {@code #root.args} for
* references to the {@link ApplicationEvent} and method arguments
* respectively.
* - Method arguments can be accessed by index. For instance the
* first argument can be accessed via {@code #root.args[0]}, {@code #p0}
* or {@code #a0}. Arguments can also be accessed by name if that
* information is available.
*
*/
String condition() default "";
}