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From dona...@apache.org
Subject cvs commit: jakarta-avalon-excalibur/loader/src/java/org/apache/excalibur/loader/runtime JoinClassLoader.java
Date Wed, 25 Sep 2002 13:40:17 GMT
donaldp     2002/09/25 06:40:17

  Added:       loader/src/java/org/apache/excalibur/loader/runtime
                        JoinClassLoader.java
  Log:
  Add in a join ClassLoader
  
  Revision  Changes    Path
  1.1                  jakarta-avalon-excalibur/loader/src/java/org/apache/excalibur/loader/runtime/JoinClassLoader.java
  
  Index: JoinClassLoader.java
  ===================================================================
  /*
   * Copyright (C) The Apache Software Foundation. All rights reserved.
   *
   * This software is published under the terms of the Apache Software License
   * version 1.1, a copy of which has been included with this distribution in
   * the LICENSE.txt file.
   */
  package org.apache.excalibur.loader.runtime;
  
  import java.io.IOException;
  import java.net.URL;
  import java.security.SecureClassLoader;
  import java.util.Enumeration;
  import java.util.Vector;
  
  /**
   * The <tt>JoinClassLoader</tt> is a {@link ClassLoader} that joins
   * a list of ClassLoaders together. The JoinClassLoader has a list of
   * ClassLoaders specified from which resources and classes can be loaded
   * from. The JoinClassLoader will attempt to load the Class or resources
   * from each ClassLoader in succession.
   *
   * <p>Note that it is recomended that each ClassLoader be made up of
   * distinct, non-overlapping sets of resources or else ClassCastExceptions
   * may result along with other undersired behaviour. </p>
   *
   * @author <a href="mailto:peter at apache.org">Peter Donald</a>
   * @version $Revision: 1.1 $ $Date: 2002/09/25 13:40:17 $
   */
  public class JoinClassLoader
      extends SecureClassLoader
  {
      /**
       * The list of classLoaders to search through
       * each time a class or resource is requested.
       */
      private final ClassLoader[] m_classLoaders;
  
      /**
       * Construct a join ClassLoader that defines parent ClassLoader
       * and list of ClassLoaders to search for classes or resources
       * when requested.
       *
       * @param parent the parent classloader
       * @param classLoaders the classloaders to search
       */
      public JoinClassLoader( final ClassLoader parent,
                              final ClassLoader[] classLoaders )
      {
          super( parent );
          if( null == classLoaders )
          {
              throw new NullPointerException( "classLoaders" );
          }
          for( int i = 0; i < classLoaders.length; i++ )
          {
              if( null == classLoaders[ i ] )
              {
                  throw new NullPointerException( "classLoaders[" + i + "]" );
              }
          }
          m_classLoaders = classLoaders;
      }
  
      /**
       * Overide findClass to find a class by searching all the
       * ClassLoaders for class.
       *
       * @param name the name of class
       * @return the Class instance
       * @throws ClassNotFoundException if unable to find class
       * @see ClassLoader#findClass
       */
      protected Class findClass( final String name )
          throws ClassNotFoundException
      {
          for( int i = 0; i < m_classLoaders.length; i++ )
          {
              try
              {
                  return m_classLoaders[ i ].loadClass( name );
              }
              catch( final ClassNotFoundException cnfe )
              {
                  //Not in that classloader
              }
          }
          return super.findClass( name );
      }
  
      /**
       * Overide findResources to retrieve all the resources
       * from all classloaders with a particular name.
       *
       * @param name the resources to search for
       * @return an enumeration of all resources with specified name
       * @throws IOException if unable to find resources
       * @see ClassLoader#findResources
       */
      protected Enumeration findResources( final String name )
          throws IOException
      {
          final Vector result = new Vector();
  
          for( int i = 0; i < m_classLoaders.length; i++ )
          {
              try
              {
                  final Enumeration resources =
                      m_classLoaders[ i ].getResources( name );
                  addAll( result, resources );
              }
              catch( final IOException ioe )
              {
                  //Not in that classloader
              }
          }
          final Enumeration resources = super.findResources( name );
          addAll( result, resources );
          return result.elements();
      }
  
      /**
       * Add all resources specified into result vector.
       *
       * @param result the result vector
       * @param resources the enumeration of resources
       */
      private void addAll( final Vector result,
                           final Enumeration resources )
      {
          while( resources.hasMoreElements() )
          {
              result.add( resources.nextElement() );
          }
      }
  
      /**
       * Overide findResource to search through all classloaders.
       *
       * @param name the resources to search for
       * @return the resource URL
       * @see ClassLoader#findResource
       */
      protected URL findResource( final String name )
      {
          for( int i = 0; i < m_classLoaders.length; i++ )
          {
              final URL resource = m_classLoaders[ i ].getResource( name );
              if( null != resource )
              {
                  return resource;
              }
          }
          return super.findResource( name );
      }
  }
  
  
  

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