1 /*
2 * Copyright 2005-2007 The Kuali Foundation
3 *
4 *
5 * Licensed under the Educational Community License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.opensource.org/licenses/ecl2.php
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.kuali.rice.core.util;
18
19 import java.util.ArrayList;
20 import java.util.List;
21
22 /**
23 * Utility class that binds/unbinds the context ClassLoader of the current Thread
24 * using a ThreadLocal.
25 * This class supports re-entrancy by maintaining a stack of context classloaders.
26 * NOTE: maybe implement stricter checks, by matching some contextual object or original
27 * classloader on bind to the unbind so that they are always matched (within a given context)
28 *
29 * @author Kuali Rice Team (rice.collab@kuali.org)
30 */
31 public final class ContextClassLoaderBinder {
32
33 private static final org.apache.log4j.Logger LOG = org.apache.log4j.Logger
34 .getLogger(ContextClassLoaderBinder.class);
35
36 /**
37 * Stack of previous context classloaders that should be
38 * restored on unbind
39 */
40 private static final ThreadLocal<List<ClassLoader>> STACK = new ThreadLocal<List<ClassLoader>>() {
41 protected List<ClassLoader> initialValue() {
42 return new ArrayList<ClassLoader>(5);
43 }
44 };
45
46 private static List<ClassLoader> getStack() {
47 return STACK.get();
48 }
49
50 public static void bind(ClassLoader cl) {
51 List<ClassLoader> stack = getStack();
52 Thread current = Thread.currentThread();
53 //log.debug("[bind] Switching CCL from " + current.getContextClassLoader() + " to " + cl);
54 // push the current context classloader on the stack
55 stack.add(current.getContextClassLoader());
56 current.setContextClassLoader(cl);
57 }
58
59 public static void unbind() {
60 List<ClassLoader> stack = getStack();
61 if (stack.size() == 0) {
62 throw new IllegalStateException("No context classloader to unbind!");
63 }
64 // pop the last context classloader off the stack
65 ClassLoader lastClassLoader = stack.get(stack.size() - 1);
66 //log.debug("[unbind] Switching CCL from " + Thread.currentThread().getContextClassLoader() + " to " + lastClassLoader);
67 stack.remove(stack.size() - 1);
68 Thread.currentThread().setContextClassLoader(lastClassLoader);
69 }
70 }