/*

  * Copyright 2005-2007 The Kuali Foundation

  * 

  * 

  * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php

  * 

  * 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.kuali.rice.core.util;

 import java.util.ArrayList;

 import java.util.List;

 /**

  * Utility class that binds/unbinds the context ClassLoader of the current Thread

  * using a ThreadLocal.

  * This class supports re-entrancy by maintaining a stack of context classloaders.

  * NOTE: maybe implement stricter checks, by matching some contextual object or original

  * classloader on bind to the unbind so that they are always matched (within a given context)

  * 

  * @author Kuali Rice Team (rice.collab@kuali.org)

  */

 public final class ContextClassLoaderBinder {

         private static final org.apache.log4j.Logger LOG = org.apache.log4j.Logger

                         .getLogger(ContextClassLoaderBinder.class);

         /**

      * Stack of previous context classloaders that should be

      * restored on unbind

      */

     private static final ThreadLocal<List<ClassLoader>> STACK = new ThreadLocal<List<ClassLoader>>() {

         protected List<ClassLoader> initialValue() {

             return new ArrayList<ClassLoader>(5);

         }

     };

     private static List<ClassLoader> getStack() {

         return STACK.get();

     }

     public static void bind(ClassLoader cl) {

         List<ClassLoader> stack = getStack();

         Thread current = Thread.currentThread();

         //log.debug("[bind] Switching CCL from " + current.getContextClassLoader() + " to " + cl);

         // push the current context classloader on the stack

         stack.add(current.getContextClassLoader());

         current.setContextClassLoader(cl);

     }

     public static void unbind() {

         List<ClassLoader> stack = getStack();

         if (stack.size() == 0) {

             throw new IllegalStateException("No context classloader to unbind!");

         }

         // pop the last context classloader off the stack

         ClassLoader lastClassLoader = stack.get(stack.size() - 1);

         //log.debug("[unbind] Switching CCL from " + Thread.currentThread().getContextClassLoader() + " to " + lastClassLoader);

         stack.remove(stack.size() - 1);

         Thread.currentThread().setContextClassLoader(lastClassLoader);

     }

 }