001    /*
002     * Copyright 2005-2007 The Kuali Foundation
003     *
004     *
005     * Licensed under the Educational Community License, Version 2.0 (the "License");
006     * you may not use this file except in compliance with the License.
007     * You may obtain a copy of the License at
008     *
009     * http://www.opensource.org/licenses/ecl2.php
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.kuali.rice.core.resourceloader;
018    
019    import java.util.ArrayList;
020    import java.util.List;
021    
022    /**
023     * Utility class that binds/unbinds the context ClassLoader of the current Thread
024     * using a ThreadLocal.
025     * This class supports re-entrancy by maintaining a stack of context classloaders.
026     * NOTE: maybe implement stricter checks, by matching some contextual object or original
027     * classloader on bind to the unbind so that they are always matched (within a given context)
028     *
029     * @author Kuali Rice Team (rice.collab@kuali.org)
030     */
031    public final class ContextClassLoaderBinder {
032    
033            /**
034         * Stack of previous context classloaders that should be
035         * restored on unbind
036         */
037        private static final ThreadLocal<List<ClassLoader>> STACK = new ThreadLocal<List<ClassLoader>>() {
038            protected List<ClassLoader> initialValue() {
039                return new ArrayList<ClassLoader>(5);
040            }
041        };
042    
043        private static List<ClassLoader> getStack() {
044            return STACK.get();
045        }
046    
047        public static void bind(ClassLoader cl) {
048            List<ClassLoader> stack = getStack();
049            Thread current = Thread.currentThread();
050            //log.debug("[bind] Switching CCL from " + current.getContextClassLoader() + " to " + cl);
051            // push the current context classloader on the stack
052            stack.add(current.getContextClassLoader());
053            current.setContextClassLoader(cl);
054        }
055    
056        public static void unbind() {
057            List<ClassLoader> stack = getStack();
058            if (stack.size() == 0) {
059                throw new IllegalStateException("No context classloader to unbind!");
060            }
061            // pop the last context classloader off the stack
062            ClassLoader lastClassLoader = stack.get(stack.size() - 1);
063            //log.debug("[unbind] Switching CCL from " + Thread.currentThread().getContextClassLoader() + " to " + lastClassLoader);
064            stack.remove(stack.size() - 1);
065            Thread.currentThread().setContextClassLoader(lastClassLoader);
066        }
067    }