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Spring Framework example source code file (IntrospectorCleanupListener.java)

This example Spring Framework source code file (IntrospectorCleanupListener.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

bean, introspectorcleanuplistener, introspectorcleanuplistener, javabean, servlet, servletcontextlistener, servletcontextlistener

The Spring Framework IntrospectorCleanupListener.java source code

/*
 * Copyright 2002-2007 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.web.util;

import java.beans.Introspector;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import org.springframework.beans.CachedIntrospectionResults;

/**
 * Listener that flushes the JDK's {@link java.beans.Introspector JavaBeans Introspector}
 * cache on web app shutdown. Register this listener in your <code>web.xml to
 * guarantee proper release of the web application class loader and its loaded classes.
 *
 * <p>If the JavaBeans Introspector has been used to analyze application classes,
 * the system-level Introspector cache will hold a hard reference to those classes.
 * Consequently, those classes and the web application class loader will not be
 * garbage-collected on web app shutdown!</b> This listener performs proper cleanup,
 * to allow for garbage collection to take effect.
 *
 * <p>Unfortunately, the only way to clean up the Introspector is to flush
 * the entire cache, as there is no way to specifically determine the
 * application's classes referenced there. This will remove cached
 * introspection results for all other applications in the server too.
 *
 * <p>Note that this listener is not necessary when using Spring's beans
 * infrastructure within the application, as Spring's own introspection results
 * cache will immediately flush an analyzed class from the JavaBeans Introspector
 * cache and only hold a cache within the application's own ClassLoader.
 *
 * <b>Although Spring itself does not create JDK Introspector leaks, note that this
 * listener should nevertheless be used in scenarios where the Spring framework classes
 * themselves reside in a 'common' ClassLoader (such as the system ClassLoader).</b>
 * In such a scenario, this listener will properly clean up Spring's introspection cache.
 *
 * <p>Application classes hardly ever need to use the JavaBeans Introspector
 * directly, so are normally not the cause of Introspector resource leaks.
 * Rather, many libraries and frameworks do not clean up the Introspector:
 * e.g. Struts and Quartz.
 *
 * <p>Note that a single such Introspector leak will cause the entire web
 * app class loader to not get garbage collected! This has the consequence that
 * you will see all the application's static class resources (like singletons)
 * around after web app shutdown, which is not the fault of those classes!
 *
 * <p>This listener should be registered as the first one in web.xml,
 * before any application listeners such as Spring's ContextLoaderListener.</b>
 * This allows the listener to take full effect at the right time of the lifecycle.
 *
 * @author Juergen Hoeller
 * @since 1.1
 * @see java.beans.Introspector#flushCaches()
 * @see org.springframework.beans.CachedIntrospectionResults#acceptClassLoader
 * @see org.springframework.beans.CachedIntrospectionResults#clearClassLoader
 */
public class IntrospectorCleanupListener implements ServletContextListener {

	public void contextInitialized(ServletContextEvent event) {
		CachedIntrospectionResults.acceptClassLoader(Thread.currentThread().getContextClassLoader());
	}

	public void contextDestroyed(ServletContextEvent event) {
		CachedIntrospectionResults.clearClassLoader(Thread.currentThread().getContextClassLoader());
		Introspector.flushCaches();
	}

}

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