/*
* 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</code> to
* guarantee proper release of the web application class loader and its loaded classes.
*
* <p><b>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 <i>not</i> 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><b>This listener should be registered as the first one in <code>web.xml</code>,
* 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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