1 /*
2 * Copyright (c) 2006, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package sun.misc;
27
28 /**
29 * Provides utility functions related to URLClassLoaders or subclasses of it.
30 *
31 * W A R N I N G
32 *
33 * This class uses undocumented, unpublished, private data structures inside
34 * java.net.URLClassLoader and sun.misc.URLClassPath. Use with extreme caution.
35 *
36 * @author tjquinn
37 */
38
39
40 import java.io.IOException;
41 import java.net.URLClassLoader;
42 import java.util.*;
43 import java.util.jar.JarFile;
44
45 public class ClassLoaderUtil {
46
47 /**
48 * Releases resources held by a URLClassLoader. A new classloader must
49 * be created before the underlying resources can be accessed again.
50 * @param classLoader the instance of URLClassLoader (or a subclass)
51 */
52 public static void releaseLoader(URLClassLoader classLoader) {
53 releaseLoader(classLoader, null);
54 }
55
56 /**
57 * Releases resources held by a URLClassLoader. Notably, close the jars
58 * opened by the loader. Initializes and updates the List of
59 * jars that have been successfully closed.
60 * <p>
61 * @param classLoader the instance of URLClassLoader (or a subclass)
62 * @param jarsClosed a List of Strings that will contain the names of jars
63 * successfully closed; can be null if the caller does not need the information returned
64 * @return a List of IOExceptions reporting jars that failed to close; null
65 * indicates that an error other than an IOException occurred attempting to
66 * release the loader; empty indicates a successful release; non-empty
67 * indicates at least one error attempting to close an open jar.
68 */
69 public static List<IOException> releaseLoader(URLClassLoader classLoader, List<String> jarsClosed) {
70
71 List<IOException> ioExceptions = new LinkedList<IOException>();
72
73 try {
74 /* Records all IOExceptions thrown while closing jar files. */
75
76 if (jarsClosed != null) {
77 jarsClosed.clear();
78 }
79
80 URLClassPath ucp = SharedSecrets.getJavaNetAccess()
81 .getURLClassPath(classLoader);
82 ArrayList<?> loaders = ucp.loaders;
83 Stack<?> urls = ucp.urls;
84 HashMap<?,?> lmap = ucp.lmap;
85
86 /*
87 *The urls variable in the URLClassPath object holds URLs that have not yet
88 *been used to resolve a resource or load a class and, therefore, do
89 *not yet have a loader associated with them. Clear the stack so any
90 *future requests that might incorrectly reach the loader cannot be
91 *resolved and cannot open a jar file after we think we've closed
92 *them all.
93 */
94 synchronized(urls) {
95 urls.clear();
96 }
97
98 /*
99 *Also clear the map of URLs to loaders so the class loader cannot use
100 *previously-opened jar files - they are about to be closed.
101 */
102 synchronized(lmap) {
103 lmap.clear();
104 }
105
106 /*
107 *The URLClassPath object's path variable records the list of all URLs that are on
108 *the URLClassPath's class path. Leave that unchanged. This might
109 *help someone trying to debug why a released class loader is still used.
110 *Because the stack and lmap are now clear, code that incorrectly uses a
111 *the released class loader will trigger an exception if the
112 *class or resource would have been resolved by the class
113 *loader (and no other) if it had not been released.
114 *
115 *The list of URLs might provide some hints to the person as to where
116 *in the code the class loader was set up, which might in turn suggest
117 *where in the code the class loader needs to stop being used.
118 *The URLClassPath does not use the path variable to open new jar
119 *files - it uses the urls Stack for that - so leaving the path variable
120 *will not by itself allow the class loader to continue handling requests.
121 */
122
123 /*
124 *For each loader, close the jar file associated with that loader.
125 *
126 *The URLClassPath's use of loaders is sync-ed on the entire URLClassPath
127 *object.
128 */
129 synchronized (ucp) {
130 for (Object o : loaders) {
131 if (o != null) {
132 /*
133 *If the loader is a JarLoader inner class and its jarFile
134 *field is non-null then try to close that jar file. Add
135 *it to the list of closed files if successful.
136 */
137 if (o instanceof URLClassPath.JarLoader) {
138 URLClassPath.JarLoader jl = (URLClassPath.JarLoader)o;
139 JarFile jarFile = jl.getJarFile();
140 try {
141 if (jarFile != null) {
142 jarFile.close();
143 if (jarsClosed != null) {
144 jarsClosed.add(jarFile.getName());
145 }
146 }
147 } catch (IOException ioe) {
148 /*
149 *Wrap the IOException to identify which jar
150 *could not be closed and add it to the list
151 *of IOExceptions to be returned to the caller.
152 */
153 String jarFileName = (jarFile == null) ? "filename not available":jarFile.getName();
154 String msg = "Error closing JAR file: " + jarFileName;
155 IOException newIOE = new IOException(msg);
156 newIOE.initCause(ioe);
157 ioExceptions.add(newIOE);
158 }
159 }
160 }
161 }
162 /*
163 *Now clear the loaders ArrayList.
164 */
165 loaders.clear();
166 }
167 } catch (Throwable t) {
168 throw new RuntimeException (t);
169 }
170 return ioExceptions;
171 }
172 }