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package javax.management.loading;

import javax.management.MBeanServer; // for Javadoc


Instances of this interface are used to keep the list of ClassLoaders
registered in an MBean Server.
They provide the necessary methods to load classes using the registered
ClassLoaders.


The first ClassLoader in a ClassLoaderRepository is
always the MBean Server's own ClassLoader.


When an MBean is registered in an MBean Server, if it is of a subclass of ClassLoader and if it does not implement the interface PrivateClassLoader, it is added to the end of the MBean Server's ClassLoaderRepository.
If it is subsequently unregistered from the MBean Server, it is
removed from the ClassLoaderRepository.


The order of MBeans in the ClassLoaderRepository is
significant.  For any two MBeans X and Y in the
ClassLoaderRepository, X must appear before
Y if the registration of X was completed before
the registration of Y started.  If X and
Y were registered concurrently, their order is indeterminate. The registration of an MBean corresponds to the call to MBeanServer.registerMBean or one of the MBeanServer.createMBean methods.


See Also:
Since:1.5
/**
 * <p>Instances of this interface are used to keep the list of ClassLoaders
 * registered in an MBean Server.
 * They provide the necessary methods to load classes using the registered
 * ClassLoaders.</p>
 *
 * <p>The first ClassLoader in a <code>ClassLoaderRepository</code> is
 * always the MBean Server's own ClassLoader.</p>
 *
 * <p>When an MBean is registered in an MBean Server, if it is of a
 * subclass of {@link java.lang.ClassLoader} and if it does not
 * implement the interface {@link PrivateClassLoader}, it is added to
 * the end of the MBean Server's <code>ClassLoaderRepository</code>.
 * If it is subsequently unregistered from the MBean Server, it is
 * removed from the <code>ClassLoaderRepository</code>.</p>
 *
 * <p>The order of MBeans in the <code>ClassLoaderRepository</code> is
 * significant.  For any two MBeans <em>X</em> and <em>Y</em> in the
 * <code>ClassLoaderRepository</code>, <em>X</em> must appear before
 * <em>Y</em> if the registration of <em>X</em> was completed before
 * the registration of <em>Y</em> started.  If <em>X</em> and
 * <em>Y</em> were registered concurrently, their order is
 * indeterminate.  The registration of an MBean corresponds to the
 * call to {@link MBeanServer#registerMBean} or one of the {@link
 * MBeanServer}<code>.createMBean</code> methods.</p>
 *
 * @see javax.management.MBeanServerFactory
 *
 * @since 1.5
 */
public interface ClassLoaderRepository {

    
Load the given class name through the list of class loaders. Each ClassLoader in turn from the ClassLoaderRepository is asked to load the class via its ClassLoader.loadClass(String) method. If it successfully returns a Class object, that is the result of this method. If it throws a ClassNotFoundException, the search continues with the next ClassLoader. If it throws another exception, the exception is propagated from this method. If the end of the list is reached, a ClassNotFoundException is thrown.


Params:
  • className – The name of the class to be loaded.
Throws:
Returns:the loaded class.
/**
     * <p>Load the given class name through the list of class loaders.
     * Each ClassLoader in turn from the ClassLoaderRepository is
     * asked to load the class via its {@link
     * ClassLoader#loadClass(String)} method.  If it successfully
     * returns a {@link Class} object, that is the result of this
     * method.  If it throws a {@link ClassNotFoundException}, the
     * search continues with the next ClassLoader.  If it throws
     * another exception, the exception is propagated from this
     * method.  If the end of the list is reached, a {@link
     * ClassNotFoundException} is thrown.</p>
     *
     * @param className The name of the class to be loaded.
     *
     * @return the loaded class.
     *
     * @exception ClassNotFoundException The specified class could not be
     *            found.
     */
    public Class<?> loadClass(String className)
            throws ClassNotFoundException;

    
Load the given class name through the list of class loaders,
excluding the given one.  Each ClassLoader in turn from the
ClassLoaderRepository, except exclude, is asked to load the class via its ClassLoader.loadClass(String) method. If it successfully returns a Class object, that is the result of this method. If it throws a ClassNotFoundException, the search continues with the next ClassLoader. If it throws another exception, the exception is propagated from this method. If the end of the list is reached, a ClassNotFoundException is thrown.


Be aware that if a ClassLoader in the ClassLoaderRepository calls this method from its 
loadClass method, it exposes itself to a deadlock if another ClassLoader in the ClassLoaderRepository does the same thing at the same time. The loadClassBefore method is recommended to avoid the risk of deadlock.


Params:
  • className – The name of the class to be loaded.
  • exclude – The class loader to be excluded. May be null, in which case this method is equivalent to 
loadClass(className).
Throws:
Returns:the loaded class.
/**
     * <p>Load the given class name through the list of class loaders,
     * excluding the given one.  Each ClassLoader in turn from the
     * ClassLoaderRepository, except <code>exclude</code>, is asked to
     * load the class via its {@link ClassLoader#loadClass(String)}
     * method.  If it successfully returns a {@link Class} object,
     * that is the result of this method.  If it throws a {@link
     * ClassNotFoundException}, the search continues with the next
     * ClassLoader.  If it throws another exception, the exception is
     * propagated from this method.  If the end of the list is
     * reached, a {@link ClassNotFoundException} is thrown.</p>
     *
     * <p>Be aware that if a ClassLoader in the ClassLoaderRepository
     * calls this method from its {@link ClassLoader#loadClass(String)
     * loadClass} method, it exposes itself to a deadlock if another
     * ClassLoader in the ClassLoaderRepository does the same thing at
     * the same time.  The {@link #loadClassBefore} method is
     * recommended to avoid the risk of deadlock.</p>
     *
     * @param className The name of the class to be loaded.
     * @param exclude The class loader to be excluded.  May be null,
     * in which case this method is equivalent to {@link #loadClass
     * loadClass(className)}.
     *
     * @return the loaded class.
     *
     * @exception ClassNotFoundException The specified class could not
     * be found.
     */
    public Class<?> loadClassWithout(ClassLoader exclude,
                                     String className)
            throws ClassNotFoundException;

    
Load the given class name through the list of class loaders, stopping at the given one. Each ClassLoader in turn from the ClassLoaderRepository is asked to load the class via its ClassLoader.loadClass(String) method. If it successfully returns a Class object, that is the result of this method. If it throws a ClassNotFoundException, the search continues with the next ClassLoader. If it throws another exception, the exception is propagated from this method. If the search reaches stop or the end of the list, a ClassNotFoundException is thrown.


Typically this method is called from the loadClass method of stop, to consult loaders that appear before it
in the ClassLoaderRepository.  By stopping the
search as soon as stop is reached, a potential
deadlock with concurrent class loading is avoided.


Params:
  • className – The name of the class to be loaded.
  • stop – The class loader at which to stop. May be null, in which case this method is equivalent to 
loadClass(className).
Throws:
Returns:the loaded class.
/**
     * <p>Load the given class name through the list of class loaders,
     * stopping at the given one.  Each ClassLoader in turn from the
     * ClassLoaderRepository is asked to load the class via its {@link
     * ClassLoader#loadClass(String)} method.  If it successfully
     * returns a {@link Class} object, that is the result of this
     * method.  If it throws a {@link ClassNotFoundException}, the
     * search continues with the next ClassLoader.  If it throws
     * another exception, the exception is propagated from this
     * method.  If the search reaches <code>stop</code> or the end of
     * the list, a {@link ClassNotFoundException} is thrown.</p>
     *
     * <p>Typically this method is called from the {@link
     * ClassLoader#loadClass(String) loadClass} method of
     * <code>stop</code>, to consult loaders that appear before it
     * in the <code>ClassLoaderRepository</code>.  By stopping the
     * search as soon as <code>stop</code> is reached, a potential
     * deadlock with concurrent class loading is avoided.</p>
     *
     * @param className The name of the class to be loaded.
     * @param stop The class loader at which to stop.  May be null, in
     * which case this method is equivalent to {@link #loadClass(String)
     * loadClass(className)}.
     *
     * @return the loaded class.
     *
     * @exception ClassNotFoundException The specified class could not
     * be found.
     *
     */
    public Class<?> loadClassBefore(ClassLoader stop,
                                    String className)
            throws ClassNotFoundException;

}