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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      */
loadClass(String className)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      */
loadClassWithout(ClassLoader exclude, String className)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      */
loadClassBefore(ClassLoader stop, String className)147     public Class<?> loadClassBefore(ClassLoader stop,
148                                     String className)
149             throws ClassNotFoundException;
150 
151 }
152