1 /*
2 * Copyright (c) 2002, 2007, 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 javax.management.loading;
27
28 import javax.management.MBeanServer; // for Javadoc
29
30 /**
31 * <p>Instances of this interface are used to keep the list of ClassLoaders
32 * registered in an MBean Server.
33 * They provide the necessary methods to load classes using the registered
34 * ClassLoaders.</p>
35 *
36 * <p>The first ClassLoader in a <code>ClassLoaderRepository</code> is
37 * always the MBean Server's own ClassLoader.</p>
38 *
39 * <p>When an MBean is registered in an MBean Server, if it is of a
40 * subclass of {@link java.lang.ClassLoader} and if it does not
41 * implement the interface {@link PrivateClassLoader}, it is added to
42 * the end of the MBean Server's <code>ClassLoaderRepository</code>.
43 * If it is subsequently unregistered from the MBean Server, it is
44 * removed from the <code>ClassLoaderRepository</code>.</p>
45 *
46 * <p>The order of MBeans in the <code>ClassLoaderRepository</code> is
47 * significant. For any two MBeans <em>X</em> and <em>Y</em> in the
48 * <code>ClassLoaderRepository</code>, <em>X</em> must appear before
49 * <em>Y</em> if the registration of <em>X</em> was completed before
50 * the registration of <em>Y</em> started. If <em>X</em> and
51 * <em>Y</em> were registered concurrently, their order is
52 * indeterminate. The registration of an MBean corresponds to the
53 * call to {@link MBeanServer#registerMBean} or one of the {@link
54 * MBeanServer}<code>.createMBean</code> methods.</p>
55 *
56 * @see javax.management.MBeanServerFactory
57 *
58 * @since 1.5
59 */
60 public interface ClassLoaderRepository {
61
62 /**
63 * <p>Load the given class name through the list of class loaders.
64 * Each ClassLoader in turn from the ClassLoaderRepository is
65 * asked to load the class via its {@link
66 * ClassLoader#loadClass(String)} method. If it successfully
67 * returns a {@link Class} object, that is the result of this
68 * method. If it throws a {@link ClassNotFoundException}, the
69 * search continues with the next ClassLoader. If it throws
70 * another exception, the exception is propagated from this
71 * method. If the end of the list is reached, a {@link
72 * ClassNotFoundException} is thrown.</p>
73 *
74 * @param className The name of the class to be loaded.
75 *
76 * @return the loaded class.
77 *
78 * @exception ClassNotFoundException The specified class could not be
79 * found.
80 */
81 public Class<?> loadClass(String className)
82 throws ClassNotFoundException;
83
84 /**
85 * <p>Load the given class name through the list of class loaders,
86 * excluding the given one. Each ClassLoader in turn from the
87 * ClassLoaderRepository, except <code>exclude</code>, is asked to
88 * load the class via its {@link ClassLoader#loadClass(String)}
89 * method. If it successfully returns a {@link Class} object,
90 * that is the result of this method. If it throws a {@link
91 * ClassNotFoundException}, the search continues with the next
92 * ClassLoader. If it throws another exception, the exception is
93 * propagated from this method. If the end of the list is
94 * reached, a {@link ClassNotFoundException} is thrown.</p>
95 *
96 * <p>Be aware that if a ClassLoader in the ClassLoaderRepository
97 * calls this method from its {@link ClassLoader#loadClass(String)
98 * loadClass} method, it exposes itself to a deadlock if another
99 * ClassLoader in the ClassLoaderRepository does the same thing at
100 * the same time. The {@link #loadClassBefore} method is
101 * recommended to avoid the risk of deadlock.</p>
102 *
103 * @param className The name of the class to be loaded.
104 * @param exclude The class loader to be excluded. May be null,
105 * in which case this method is equivalent to {@link #loadClass
106 * loadClass(className)}.
107 *
108 * @return the loaded class.
109 *
110 * @exception ClassNotFoundException The specified class could not
111 * be found.
112 */
113 public Class<?> loadClassWithout(ClassLoader exclude,
114 String className)
115 throws ClassNotFoundException;
116
117 /**
118 * <p>Load the given class name through the list of class loaders,
119 * stopping at the given one. Each ClassLoader in turn from the
120 * ClassLoaderRepository is asked to load the class via its {@link
121 * ClassLoader#loadClass(String)} method. If it successfully
122 * returns a {@link Class} object, that is the result of this
123 * method. If it throws a {@link ClassNotFoundException}, the
124 * search continues with the next ClassLoader. If it throws
125 * another exception, the exception is propagated from this
126 * method. If the search reaches <code>stop</code> or the end of
127 * the list, a {@link ClassNotFoundException} is thrown.</p>
128 *
129 * <p>Typically this method is called from the {@link
130 * ClassLoader#loadClass(String) loadClass} method of
131 * <code>stop</code>, to consult loaders that appear before it
132 * in the <code>ClassLoaderRepository</code>. By stopping the
133 * search as soon as <code>stop</code> is reached, a potential
134 * deadlock with concurrent class loading is avoided.</p>
135 *
136 * @param className The name of the class to be loaded.
137 * @param stop The class loader at which to stop. May be null, in
138 * which case this method is equivalent to {@link #loadClass(String)
139 * loadClass(className)}.
140 *
141 * @return the loaded class.
142 *
143 * @exception ClassNotFoundException The specified class could not
144 * be found.
145 *
146 */
147 public Class<?> loadClassBefore(ClassLoader stop,
148 String className)
149 throws ClassNotFoundException;
150
151 }