1 /*
2 * Grapht, an open source dependency injector.
3 * Copyright 2014-2015 various contributors (see CONTRIBUTORS.txt)
4 * Copyright 2010-2014 Regents of the University of Minnesota
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU Lesser General Public License as
8 * published by the Free Software Foundation; either version 2.1 of the
9 * License, or (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
13 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
14 * details.
15 *
16 * You should have received a copy of the GNU General Public License along with
17 * this program; if not, write to the Free Software Foundation, Inc., 51
18 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
19 */
20 package org.grouplens.grapht.util;
21
22 /**
23 * Utility methods for class loaders.
24 * @author <a href="http://www.grouplens.org">GroupLens Research</a>
25 * @since 0.8.1
26 */
27 public final class ClassLoaders {
28 private ClassLoaders() {}
29
30 /**
31 * Infer a default class loader.
32 * @return A reasonable default class loader.
33 */
34 public static ClassLoader inferDefault() {
35 return inferDefault(ClassLoaders.class);
36 }
37
38 /**
39 * Infer a default class loader.
40 * @param refClass a reference class to use for looking up the class loader. If there is not
41 * a context class loader on the current thread, the class loader used to load
42 * this class is returned.
43 * @return A reasonable default class loader.
44 */
45 public static ClassLoader inferDefault(Class<?> refClass) {
46 ClassLoader loader = Thread.currentThread().getContextClassLoader();
47 if (loader == null) {
48 loader = refClass.getClassLoader();
49 }
50 if (loader == null) {
51 loader = ClassLoader.getSystemClassLoader();
52 }
53 return loader;
54 }
55
56 /**
57 * Use the specified class loader for the current thread's context class loader. This method
58 * returns a context to make it easy to restore the original class loader. Example usage:
59 *
60 * {@code
61 * ClassLoaderContext context = ClassLoaders.pushContext(classLoader);
62 * try {
63 * // some code with classLoader as the current loader
64 * } finally {
65 * context.pop();
66 * }
67 * }
68 *
69 * @param loader The class loader to use.
70 * @return A context for restoring the original class loader.
71 */
72 public static ClassLoaderContext pushContext(ClassLoader loader) {
73 return pushContext(Thread.currentThread(), loader);
74 }
75
76 /**
77 * Use the specified class loader for the given thread's context class loader.
78 *
79 * @param thread The thread whose class loader should be modified.
80 * @param loader The class loader to use.
81 * @return A context for restoring the original class loader.
82 * @see #pushContext(ClassLoader)
83 */
84 public static ClassLoaderContext pushContext(Thread thread, ClassLoader loader) {
85 ClassLoader orig = thread.getContextClassLoader();
86 ClassLoaderContext context = new ClassLoaderContext(thread, orig);
87 thread.setContextClassLoader(loader);
88 return context;
89 }
90 }