/*==========================================================================*\
| $Id: DelegatingUrlClassLoader.java,v 1.2 2012/03/28 13:48:08 stedwar2 Exp $
|*-------------------------------------------------------------------------*|
| Copyright (C) 2006-2012 Virginia Tech
|
| This file is part of Web-CAT.
|
| Web-CAT is free software; you can redistribute it and/or modify
| it under the terms of the GNU Affero General Public License as published
| by the Free Software Foundation; either version 3 of the License, or
| (at your option) any later version.
|
| Web-CAT is distributed in the hope that it will be useful,
| but WITHOUT ANY WARRANTY; without even the implied warranty of
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
| GNU General Public License for more details.
|
| You should have received a copy of the GNU Affero General Public License
| along with Web-CAT; if not, see <http://www.gnu.org/licenses/>.
\*==========================================================================*/
package org.webcat.core;
import java.net.URL;
import java.net.URLClassLoader;
import org.webcat.core.DelegatingUrlClassLoader;
import org.apache.log4j.Logger;
// -------------------------------------------------------------------------
/**
* The central loading point for all Web-CAT subsystem classes.
* [Note--this class is intended for supporting plugin-style jar'ed
* subsystems instead of WebObjects Framework-based subsystems. Since we
* aren't using such jar'ed subsystems at present, this is really just a
* shell for future expandability/flexibility.]
*
* <p>
* Web-CAT needs a centralized class loader for all the JAR files to simplify
* life, since class names are stored in the database and we need a way to
* instantiate them. We can't use the system class loader, since it offers
* no way to "plug-in" additional class loaders.
* </p>
*
* <p>
* Instead, we have this delegating class loader. It searches through all
* URLs (as specified through addURL()) to find a class. If it isn't found,
* then the System class loader is consulted. If it still isn't found, the
* class wasn't loaded.
* </p>
*
* <p>
* Additionally, to keep Web-CAT simple, we only have one of these class
* loaders running around. This allows a single class loader to be used to
* load all classes used in Web-CAT.
* </p>
*
* @author Stephen Edwards
* @author Last changed by $Author: stedwar2 $
* @version $Revision: 1.2 $, $Date: 2012/03/28 13:48:08 $
*/
public class DelegatingUrlClassLoader
extends URLClassLoader
{
//~ Constructors ..........................................................
// ----------------------------------------------------------
/**
* Keep anyone from instantiating this class loader.
*/
protected DelegatingUrlClassLoader()
{
super( new URL[] { },
// ClassLoader.getSystemClassLoader()
// Modified to work with WO 5.2 WOBootstrap code
// Thread.currentThread().getContextClassLoader()
DelegatingUrlClassLoader.class.getClassLoader()
);
// log.debug( "constructor: my chain" );
// ClassLoader c = this;
// while ( c != null )
// {
// log.debug( "\tloader => " + c );
// c = c.getParent();
// }
// log.debug( "from class:" );
// c = DelegatingUrlClassLoader.class.getClassLoader();
// while ( c != null )
// {
// log.debug( "\tloader => " + c );
// c = c.getParent();
// }
}
//~ Methods ...............................................................
// ----------------------------------------------------------
/**
* @return Singleton instance of the delegating URL class loader.
*/
public static DelegatingUrlClassLoader getClassLoader()
{
if ( me == null )
{
// log.debug( "Before creation, from class:" );
// ClassLoader c = DelegatingUrlClassLoader.class.getClassLoader();
// while ( c != null )
// {
// log.debug( "\tloader => " + c );
// c = c.getParent();
// }
me = new DelegatingUrlClassLoader();
}
return me;
}
// ----------------------------------------------------------
/**
* Add a URL to the list of URLs searched for classes.
*
* @param u The URL to add.
*/
public void addURL( URL u )
{
super.addURL( u );
}
//~ Instance/static variables .............................................
private static DelegatingUrlClassLoader me;
static Logger log = Logger.getLogger( DelegatingUrlClassLoader.class );
}