Utility class for users of commons-logging in webapps.

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/logging/trunk@190896 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/logging/impl/ServletContextCleaner.java

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+/*
+ * Copyright 2005 The Apache Software Foundation.
+ * 
+ * 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.apache.commons.logging.impl;
+
+import javax.servlet.ServletContextListener;
+import javax.servlet.ServletContextEvent;
+
+import org.apache.commons.logging.LogFactory;
+
+
+/**
+ * This class is capable of receiving notifications about the undeployment of
+ * a webapp, and responds by ensuring that commons-logging releases all
+ * memory associated with the undeployed webapp.
+ * <p>
+ * This class is necessary when code using commons-logging is deployed within
+ * a servlet container and commons-logging is deployed via a shared classloader.
+ * When commons-logging is deployed in a "shared" classloader that is visible 
+ * to all webapps, commons-logging still ensures that each webapp gets its own
+ * logging configuration by setting up a separate LogFactory object for each 
+ * context classloader, and ensuring that the correct LogFactory object is 
+ * used based on the context classloader set whenever LogFactory.getLog is 
+ * called. However the negative side of this is that LogFactory needs to keep 
+ * a static map of LogFactory objects keyed by context classloader; when the 
+ * webapp is "undeployed" this means there is still a reference to the 
+ * undeployed classloader preventing the memory used by all its classes from 
+ * being reclaimed.  
+ * <p>
+ * To use this class, configure the webapp deployment descriptor to call
+ * this class on webapp undeploy; the contextDestroyed method will tell
+ * LogFactory that the entry in its map for the current webapp's context
+ * classloader should be cleared.
+ */
+
+public class ServletContextCleaner implements ServletContextListener {
+    
+    /**
+     * Invoked when a webapp is undeployed, this tells the LogFactory
+     * class to release any logging information related to the current
+     * contextClassloader.
+     */
+    public void contextDestroyed(ServletContextEvent sce) {
+        LogFactory.release(Thread.currentThread().getContextClassLoader());
+    }
+    
+    /**
+     * Invoked when a webapp is deployed. Nothing needs to be done here.
+     */
+    public void contextInitialized(ServletContextEvent sce) {
+        // do nothing
+    }
+}