001    /*
002     * Copyright 2005 Stephen J. McConnell.
003     *
004     * Licensed  under the  Apache License,  Version 2.0  (the "License");
005     * you may not use  this file  except in  compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     *   http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed  under the  License is distributed on an "AS IS" BASIS,
012     * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY KIND, either  express  or
013     * implied.
014     *
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    
019    package net.dpml.lang;
020    
021    import java.io.File;
022    import java.io.IOException;
023    import java.net.URI;
024    import java.net.URL;
025    import java.util.List;
026    import java.util.Arrays;
027    
028    /**
029     * The SystemClassLoader is a URLClassLoader that supports late binding of 
030     * URLs.  This class may be configured as the system classloader when loading plugins
031     * that declare system category plugin entries.
032     *
033     * @author <a href="http://www.dpml.net">Digital Product Meta Library</a>
034     * @version 1.0.2
035     */
036    public final class SystemClassLoader extends StandardClassLoader 
037    {
038        private final ClassLoader m_parent;
039        
040       /**
041        * Creation of a new system classloader.
042        *
043        * @param parent the parent classloader
044        */
045        public SystemClassLoader( ClassLoader parent )
046        {
047            super( "system", Category.SYSTEM, new URL[0], parent );
048            
049            m_parent = parent;
050            
051            if( "true".equals( System.getProperty( "dpml.transit.include.tools" ) ) )
052            {
053                String jrePath = System.getProperty( "java.home" );
054                try
055                {
056                    File jre = new File( jrePath );
057                    File jdk = jre.getParentFile();
058                    File lib = new File( jdk, "lib" );
059                    File jar = new File( lib, "tools.jar" );
060                    URL url = jar.toURL();
061                    addURL( url );
062                }
063                catch( Throwable e )
064                {
065                    final String error = 
066                      "Internal error while attempting to establish tools.jar in the system classloader.";
067                    throw new PartError( error, e );
068                }
069            }
070        }
071        
072        synchronized void addDelegates( final URI[] uris ) throws IOException
073        {
074            URL[] urls = toURLs( uris );
075            URL[] local = super.getURLs();
076            List list = Arrays.asList( local );
077            for( int i=0; i<urls.length; i++ )
078            {
079                URL url = urls[i];
080                if( !list.contains( url ) )
081                {
082                    try
083                    {
084                        url.getContent();
085                        addURL( url );
086                    }
087                    catch( Exception e )
088                    {
089                        final String error = 
090                          "Failed to resolve url " + url;
091                        System.err.println( error );
092                    }
093                }
094            }
095        }
096    }
097