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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.xbean.classloader;

import java.beans.Introspector;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamClass;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Map;

/**
 * Utility methods for class loader manipulation in a server environment.
 * 
 * @author Dain Sundstrom
 */
public final class ClassLoaderUtil {

	private ClassLoaderUtil() {
	}

	/**
	 * Cleans well known class loader leaks in VMs and libraries. There is a lot of bad code out there and this method
	 * will clear up the known problems. This method should only be called when the class loader will no longer be used.
	 * It this method is called two often it can have a serious impact on performance.
	 * @param classLoader the class loader to destroy
	 */
	public static void destroy(ClassLoader classLoader) {
		releaseCommonsLoggingCache(classLoader);
		clearSunSoftCache(ObjectInputStream.class, "subclassAudits");
		clearSunSoftCache(ObjectOutputStream.class, "subclassAudits");
		clearSunSoftCache(ObjectStreamClass.class, "localDescs");
		clearSunSoftCache(ObjectStreamClass.class, "reflectors");
		Introspector.flushCaches();
	}

	/**
	 * Clears the caches maintained by the SunVM object stream implementation. This method uses reflection and
	 * setAccessable to obtain access to the Sun cache. The cache is locked with a synchronize monitor and cleared. This
	 * method completely clears the class loader cache which will impact performance of object serialization.
	 * @param clazz the name of the class containing the cache field
	 * @param fieldName the name of the cache field
	 */
	public static void clearSunSoftCache(Class clazz, String fieldName) {
		Map cache = null;
		try {
			Field field = clazz.getDeclaredField(fieldName);
			field.setAccessible(true);
			cache = (Map) field.get(null);
		} catch (Throwable ignored) {
			// there is nothing a user could do about this anyway
		}

		if (cache != null) {
			synchronized (cache) {
				cache.clear();
			}
		}
	}

	/**
	 * Releases the specified classloader from the Apache Jakarta Commons Logging class loader cache using reflection.
	 * @param classLoader the class loader to release
	 */
	public static void releaseCommonsLoggingCache(ClassLoader classLoader) {
		try {
			Class logFactory = classLoader.loadClass("org.apache.commons.logging.LogFactory");
			Method release = logFactory.getMethod("release", new Class[] { ClassLoader.class });
			release.invoke(null, new Object[] { classLoader });
		} catch (Throwable ignored) {
			// there is nothing a user could do about this anyway
		}
	}
}