View Javadoc
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 }