org.springframework.context.event.AbstractApplicationEventMulticaster Maven / Gradle / Ivy
/*
* Copyright 2002-2006 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.util.Collection;
import org.springframework.beans.BeanUtils;
import org.springframework.context.ApplicationListener;
import org.springframework.core.CollectionFactory;
/**
* Abstract implementation of the ApplicationEventMulticaster interface,
* providing the basic listener registration facility.
*
* Doesn't permit multiple instances of the same listener by default,
* as it keeps listeners in a linked Set. The collection class used to hold
* ApplicationListener objects can be overridden through the "collectionClass"
* bean property.
*
*
Note that this class doesn't try to do anything clever to ensure thread
* safety if listeners are added or removed at runtime. A technique such as
* Copy-on-Write (Lea:137) could be used to ensure this, but the assumption in
* the basic version of the class is that listeners will be added at application
* configuration time and not added or removed as the application runs.
*
*
A custom collection class must be specified to allow for thread-safe
* runtime registration of listeners. A good candidate for this is Doug Lea's
* java.util.concurrent.CopyOnWriteArraySet or its non-JDK predecessor,
* EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArraySet (or the
* respective CopyOnWriteArrayList version, allowing for registering the same
* listener multiple times). Those classes provide a thread-safe Iterator,
* optimized for read-mostly usage - matching this use case nicely.
*
*
Implementing ApplicationEventMulticaster's actual multicastEvent
* method is left to subclasses. SimpleApplicationEventMulticaster simply multicasts
* all events to all registered listeners, invoking them in the calling thread.
* Alternative implementations could be more sophisticated in those respects.
*
* @author Juergen Hoeller
* @since 1.2.3
* @see #setCollectionClass
* @see #getApplicationListeners()
* @see SimpleApplicationEventMulticaster
*/
public abstract class AbstractApplicationEventMulticaster implements ApplicationEventMulticaster {
/** Collection of ApplicationListeners */
private Collection applicationListeners = CollectionFactory.createLinkedSetIfPossible(16);
/**
* Specify the collection class to use. Can be populated with a fully
* qualified class name when defined in a Spring application context.
*
Default is a linked HashSet, keeping the registration order.
* If no linked Set implementation is available, a plain HashSet will
* be used as fallback (not keeping the registration order).
*
Note that a Set class specified will not permit multiple instances
* of the same listener, while a List class will allow for registering
* the same listener multiple times.
*
Consider Doug Lea's java.util.concurrent.CopyOnWriteArraySet or its
* non-JDK predecessor, EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArraySet
* (or the respective CopyOnWriteArrayList version). Those classes provide a thread-safe
* Iterator, optimized for read-mostly usage - matching this use case nicely.
* @see org.springframework.core.CollectionFactory#createLinkedSetIfPossible
* @see java.util.concurrent.CopyOnWriteArraySet
* @see EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArraySet
*/
public void setCollectionClass(Class collectionClass) {
if (collectionClass == null) {
throw new IllegalArgumentException("collectionClass must not be null");
}
if (!Collection.class.isAssignableFrom(collectionClass)) {
throw new IllegalArgumentException("collectionClass must implement [java.util.Collection]");
}
// Create desired collection instance.
// Add all previously registered listeners (usually none).
Collection newColl = (Collection) BeanUtils.instantiateClass(collectionClass);
newColl.addAll(this.applicationListeners);
this.applicationListeners = newColl;
}
public void addApplicationListener(ApplicationListener listener) {
this.applicationListeners.add(listener);
}
public void removeApplicationListener(ApplicationListener listener) {
this.applicationListeners.remove(listener);
}
public void removeAllListeners() {
this.applicationListeners.clear();
}
/**
* Return the current Collection of ApplicationListeners.
*
Note that this is the raw Collection of ApplicationListeners,
* potentially modified when new listeners get registered or
* existing ones get removed. This Collection is not a snapshot copy.
* @return a Collection of ApplicationListeners
* @see org.springframework.context.ApplicationListener
*/
protected Collection getApplicationListeners() {
return applicationListeners;
}
}