01: /*
02: * Copyright 2002-2007 the original author or authors.
03: *
04: * Licensed under the Apache License, Version 2.0 (the "License");
05: * you may not use this file except in compliance with the License.
06: * You may obtain a copy of the License at
07: *
08: * http://www.apache.org/licenses/LICENSE-2.0
09: *
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;
20:
21: import javax.servlet.ServletContextEvent;
22: import javax.servlet.ServletContextListener;
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
73: ServletContextListener {
74:
75: public void contextInitialized(ServletContextEvent event) {
76: CachedIntrospectionResults.acceptClassLoader(Thread
77: .currentThread().getContextClassLoader());
78: }
79:
80: public void contextDestroyed(ServletContextEvent event) {
81: CachedIntrospectionResults.clearClassLoader(Thread
82: .currentThread().getContextClassLoader());
83: Introspector.flushCaches();
84: }
85:
86: }
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