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Posted to dev@commons.apache.org by rd...@apache.org on 2003/07/07 23:58:45 UTC
cvs commit: jakarta-commons/beanutils/src/java/org/apache/commons/beanutils ContextClassLoaderLocal.java
rdonkin 2003/07/07 14:58:45
Added: beanutils/src/java/org/apache/commons/beanutils
ContextClassLoaderLocal.java
Log:
Factored out context classloading logic into separate class. This allows it to be more easily used. Patch contributed by Eric Pabst.
Revision Changes Path
1.1 jakarta-commons/beanutils/src/java/org/apache/commons/beanutils/ContextClassLoaderLocal.java
Index: ContextClassLoaderLocal.java
===================================================================
/*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 1999-2003 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact apache@apache.org.
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Group.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.commons.beanutils;
import java.util.Map;
import java.util.WeakHashMap;
/**
* A value that is provided per (thread) context classloader.
* Patterned after ThreadLocal.
* There is a separate value used when Thread.getContextClassLoader() is null.
* This mechanism provides isolation for web apps deployed in the same container.
* <strong>Note:</strong> A WeakHashMap bug in several 1.3 JVMs results in a memory leak
* for those JVMs.
*
* @see Thread#getContextClassLoader().
* @author Eric Pabst
*/
public class ContextClassLoaderLocal {
private Map valueByClassLoader = new WeakHashMap();
private boolean globalValueInitialized = false;
private Object globalValue;
public ContextClassLoaderLocal() {
super();
}
/**
* Returns the initial value for this ContextClassLoaderLocal
* variable. This method will be called once per Context ClassLoader for
* each ContextClassLoaderLocal, the first time it is accessed
* with get or set. If the programmer desires ContextClassLoaderLocal variables
* to be initialized to some value other than null, ContextClassLoaderLocal must
* be subclassed, and this method overridden. Typically, an anonymous
* inner class will be used. Typical implementations of initialValue
* will call an appropriate constructor and return the newly constructed
* object.
*
* @return a new Object to be used as an initial value for this ContextClassLoaderLocal
*/
protected Object initialValue() {
return null;
}
/**
* Gets the instance which provides the functionality for {@link BeanUtils}.
* This is a pseudo-singleton - an single instance is provided per (thread) context classloader.
* This mechanism provides isolation for web apps deployed in the same container.
* @return the object currently associated with the
*/
public synchronized Object get() {
// synchronizing the whole method is a bit slower
// but guarentees no subtle threading problems, and there's no
// need to synchronize valueByClassLoader
// make sure that the map is given a change to purge itself
valueByClassLoader.isEmpty();
try {
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
if (contextClassLoader != null) {
Object value = valueByClassLoader.get(contextClassLoader);
if ((value == null)
&& !valueByClassLoader.containsKey(contextClassLoader)) {
value = initialValue();
valueByClassLoader.put(contextClassLoader, value);
}
return value;
}
} catch (SecurityException e) { /* SWALLOW - should we log this? */ }
// if none or exception, return the globalValue
if (!globalValueInitialized) {
globalValue = initialValue();
globalValueInitialized = true;
}//else already set
return globalValue;
}
/**
* Sets the value - a value is provided per (thread) context classloader.
* This mechanism provides isolation for web apps deployed in the same container.
*
* @param value the object to be associated with the entrant thread's context classloader
*/
public synchronized void set(Object value) {
// synchronizing the whole method is a bit slower
// but guarentees no subtle threading problems
// make sure that the map is given a change to purge itself
valueByClassLoader.isEmpty();
try {
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
if (contextClassLoader != null) {
valueByClassLoader.put(contextClassLoader, value);
return;
}
} catch (SecurityException e) { /* SWALLOW - should we log this? */ }
// if in doubt, set the global value
globalValue = value;
globalValueInitialized = true;
}
/**
* Unsets the value associated with the current thread's context classloader
*/
public synchronized void unset() {
try {
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
unset(contextClassLoader);
} catch (SecurityException e) { /* SWALLOW - should we log this? */ }
}
/**
* Unsets the value associated with the given classloader
*/
public synchronized void unset(ClassLoader classLoader) {
valueByClassLoader.remove(classLoader);
}
}
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