001/**
002 * Logback: the reliable, generic, fast and flexible logging framework.
003 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
004 *
005 * This program and the accompanying materials are dual-licensed under
006 * either the terms of the Eclipse Public License v1.0 as published by
007 * the Eclipse Foundation
008 *
009 *   or (per the licensee's choosing)
010 *
011 * under the terms of the GNU Lesser General Public License version 2.1
012 * as published by the Free Software Foundation.
013 */
014package ch.qos.logback.classic.spi;
015
016import java.net.URL;
017import java.net.URLClassLoader;
018
019/**
020 * An almost trivial no fuss implementation of a class loader following the
021 * child-first delegation model.
022 * 
023 * @author Ceki Gulcu
024 */
025public class LocalFirstClassLoader extends URLClassLoader {
026
027    public LocalFirstClassLoader(URL[] urls) {
028        super(urls);
029    }
030
031    public LocalFirstClassLoader(URL[] urls, ClassLoader parent) {
032        super(urls, parent);
033    }
034
035    public void addURL(URL url) {
036        super.addURL(url);
037    }
038
039    public Class<?> loadClass(String name) throws ClassNotFoundException {
040        return loadClass(name, false);
041    }
042
043    /**
044     * We override the parent-first behavior established by java.lang.Classloader.
045     * 
046     * The implementation is surprisingly straightforward.
047     */
048    protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
049
050        // First, check if the class has already been loaded
051        Class<?> c = findLoadedClass(name);
052
053        // if not loaded, search the local (child) resources
054        if (c == null) {
055            try {
056                c = findClass(name);
057            } catch (ClassNotFoundException cnfe) {
058                // ignore
059            }
060        }
061
062        // if we could not find it, delegate to parent
063        // Note that we don't attempt to catch any ClassNotFoundException
064        if (c == null) {
065            if (getParent() != null) {
066                c = getParent().loadClass(name);
067            } else {
068                c = getSystemClassLoader().loadClass(name);
069            }
070        }
071
072        if (resolve) {
073            resolveClass(c);
074        }
075
076        return c;
077    }
078}