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Java > Open Source Codes > org > springframework > web > util > IntrospectorCleanupListener


1 /*
2  * Copyright 2002-2007 the original author or authors.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */

16
17 package org.springframework.web.util;
18
19 import java.beans.Introspector JavaDoc;
20
21 import javax.servlet.ServletContextEvent JavaDoc;
22 import javax.servlet.ServletContextListener JavaDoc;
23
24 import org.springframework.beans.CachedIntrospectionResults;
25
26 /**
27  * Listener that flushes the JDK's {@link java.beans.Introspector JavaBeans Introspector}
28  * cache on web app shutdown. Register this listener in your <code>web.xml</code> to
29  * guarantee proper release of the web application class loader and its loaded classes.
30  *
31  * <p><b>If the JavaBeans Introspector has been used to analyze application classes,
32  * the system-level Introspector cache will hold a hard reference to those classes.
33  * Consequently, those classes and the web application class loader will not be
34  * garbage-collected on web app shutdown!</b> This listener performs proper cleanup,
35  * to allow for garbage collection to take effect.
36  *
37  * <p>Unfortunately, the only way to clean up the Introspector is to flush
38  * the entire cache, as there is no way to specifically determine the
39  * application's classes referenced there. This will remove cached
40  * introspection results for all other applications in the server too.
41  *
42  * <p>Note that this listener is <i>not</i> necessary when using Spring's beans
43  * infrastructure within the application, as Spring's own introspection results
44  * cache will immediately flush an analyzed class from the JavaBeans Introspector
45  * cache and only hold a cache within the application's own ClassLoader.
46  *
47  * <b>Although Spring itself does not create JDK Introspector leaks, note that this
48  * listener should nevertheless be used in scenarios where the Spring framework classes
49  * themselves reside in a 'common' ClassLoader (such as the system ClassLoader).</b>
50  * In such a scenario, this listener will properly clean up Spring's introspection cache.
51  *
52  * <p>Application classes hardly ever need to use the JavaBeans Introspector
53  * directly, so are normally not the cause of Introspector resource leaks.
54  * Rather, many libraries and frameworks do not clean up the Introspector:
55  * e.g. Struts and Quartz.
56  *
57  * <p>Note that a single such Introspector leak will cause the entire web
58  * app class loader to not get garbage collected! This has the consequence that
59  * you will see all the application's static class resources (like singletons)
60  * around after web app shutdown, which is not the fault of those classes!
61  *
62  * <p><b>This listener should be registered as the first one in <code>web.xml</code>,
63  * before any application listeners such as Spring's ContextLoaderListener.</b>
64  * This allows the listener to take full effect at the right time of the lifecycle.
65  *
66  * @author Juergen Hoeller
67  * @since 1.1
68  * @see java.beans.Introspector#flushCaches()
69  * @see org.springframework.beans.CachedIntrospectionResults#acceptClassLoader
70  * @see org.springframework.beans.CachedIntrospectionResults#clearClassLoader
71  */

72 public class IntrospectorCleanupListener implements ServletContextListener JavaDoc {
73
74     public void contextInitialized(ServletContextEvent JavaDoc event) {
75         CachedIntrospectionResults.acceptClassLoader(Thread.currentThread().getContextClassLoader());
76     }
77
78     public void contextDestroyed(ServletContextEvent JavaDoc event) {
79         CachedIntrospectionResults.clearClassLoader(Thread.currentThread().getContextClassLoader());
80         Introspector.flushCaches();
81     }
82
83 }
84
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