proposal/mutant/src/main/org/apache/ant/core/support/AntClassLoader.java

/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Ant", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Group.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package org.apache.ant.core.support;

import java.util.*;
import java.net.*;
import java.io.*;

/**
 * The AntClassLoader is a type of URL classloader which reverses the standard
 * lookup order to load things from the URLs first and then to use the parent class
 * loader only if the class does not exist in the URLs.
 *
 * @author <a href="mailto:conor@apache.org">Conor MacNeill</a>
 */ 
public class AntClassLoader extends URLClassLoader {
    /** A Debug label to print when the Classloader finds or fails to find a class. */
    private String debugLabel = null;
    
    /** A flag whihc controls whether messages are logged by the loader */
    private boolean debug = false;

    private void dumpURLs() {
        if (debug && debugLabel != null) {
            System.out.println(debugLabel + ": loader URLs");
            URL[] urls = getURLs();
            for (int i = 0; i < urls.length; ++i) {
                System.out.println(debugLabel + ": URL: " + urls[i]);
            }
        }
    }        
    
    public AntClassLoader(URL[] urls) {
        super(urls);
    }

    public AntClassLoader(URL[] urls, String debugLabel) {
        super(urls);
        this.debugLabel = debugLabel;
    }

    public AntClassLoader(URL[] urls,
                          ClassLoader parent) {
        super(urls, parent);
    }
    
    public AntClassLoader(URL[] urls,
                          ClassLoader parent, String debugLabel) {
        super(urls, parent);
        this.debugLabel = debugLabel;
    }
    
    public void setDebug(boolean debug) {
        this.debug = debug;
        dumpURLs();    
    }

    protected Class loadClass(String name, boolean resolve) 
            throws ClassNotFoundException {
        if (debug && debugLabel != null) {                
            System.out.println(debugLabel + ": Trying to load class " + name);
        }

        Class c = findLoadedClass(name);
        if (c == null) {
            try {
                c = findClass(name);
                if (debug && debugLabel != null) {
                    System.out.println(debugLabel + ": Found class " + name + " in this loader");
                }
            } catch (ClassNotFoundException e) {
                c = super.loadClass(name, resolve);
                if (debug && debugLabel != null) {
                    System.out.println(debugLabel + ": Found class " + name + " in parent loader");
                }
                return c;
            }
        }
        if (resolve) {
            resolveClass(c);
        }
        return c;
    }
        
    public void addURL(URL url) {
        super.addURL(url);
    }

    public URL getResource(String name) {
        URL url = findResource(name);
        if (url == null) {
            url = super.getResource(name);
        }
        
        return url;
    }
}