AntClassLoader.java

/*******************************************************************************
 * Copyright (c) 2000, 2013 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Tom Tromey (tromey@redhat.com) - patch for bug 40972
 *******************************************************************************/
package org.eclipse.ant.internal.core;

import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;

public class AntClassLoader extends URLClassLoader {

	private static final String ANT_PACKAGES_PREFIX = "org.apache.tools"; //$NON-NLS-1$
	private static final String ANT_URL_PREFIX = "org/apache/tools"; //$NON-NLS-1$

	private boolean fAllowPluginLoading = false;

	protected ClassLoader[] fPluginLoaders;

	private ClassLoader fContextClassloader = null;

	public AntClassLoader(URL[] urls, ClassLoader[] pluginLoaders) {
		super(urls, ClassLoader.getSystemClassLoader());
		fPluginLoaders = pluginLoaders;
	}

	/*
	 * @see java.net.URLClassLoader#findClass(java.lang.String)
	 */
	@Override
	protected Class<?> findClass(String name) throws ClassNotFoundException {
		Class<?> result = null;
		// check whether to load the Apache Ant classes from the plug-in class loaders
		// or to only load from the URLs specified from the Ant runtime classpath preferences setting
		if (fAllowPluginLoading || !(name.startsWith(ANT_PACKAGES_PREFIX))) {
			result = loadClassPlugins(name);
		}

		if (result != null) {
			return result;
		}

		return super.findClass(name);
	}

	protected Class<?> loadClassPlugins(String name) {
		// remove this class loader as the context class loader
		// when loading classes from plug-ins...see bug 94471
		ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader();
		if (fContextClassloader != null) {
			Thread.currentThread().setContextClassLoader(fContextClassloader);
		}
		try {
			Class<?> result = null;
			if (fPluginLoaders != null) {
				for (int i = 0; (i < fPluginLoaders.length) && (result == null); i++) {
					try {
						result = fPluginLoaders[i].loadClass(name);
					}
					catch (ClassNotFoundException e) {
						// Ignore exception now. If necessary we'll throw
						// a ClassNotFoundException in loadClass(String)
					}
				}
			}
			return result;
		}
		finally {
			Thread.currentThread().setContextClassLoader(originalClassLoader);
		}
	}

	/*
	 * @see java.net.URLClassLoader#findResource(java.lang.String)
	 */
	@Override
	public URL findResource(String name) {
		if (fAllowPluginLoading || !(name.startsWith(ANT_URL_PREFIX))) {
			URL result = findResourcePlugins(name);
			if (result != null) {
				return result;
			}
		}

		return super.findResource(name);
	}

	private URL findResourcePlugins(String name) {
		// remove this class loader as the context class loader
		// when loading resources from plug-ins...see bug 94471
		ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader();
		if (fContextClassloader != null) {
			Thread.currentThread().setContextClassLoader(fContextClassloader);
		}
		try {
			URL result = null;
			if (fPluginLoaders != null) {
				for (int i = 0; i < fPluginLoaders.length; i++) {
					result = fPluginLoaders[i].getResource(name);
					if (result != null) {
						return result;
					}
				}
			}
		}
		finally {
			Thread.currentThread().setContextClassLoader(originalClassLoader);
		}
		return null;
	}

	/*
	 * @see java.net.URLClassLoader#findResources(java.lang.String)
	 */
	@Override
	public Enumeration<URL> findResources(String name) throws IOException {
		ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader();
		if (fContextClassloader != null) {
			Thread.currentThread().setContextClassLoader(fContextClassloader);
		}
		ArrayList<URL> all = new ArrayList<>();
		try {
			if (fAllowPluginLoading || !(name.startsWith(ANT_URL_PREFIX) || name.startsWith(ANT_URL_PREFIX, 1))) {
				if (fPluginLoaders != null) {
					Enumeration<URL> result = null;
					for (int i = 0; i < fPluginLoaders.length; i++) {
						result = fPluginLoaders[i].getResources(name);
						while (result.hasMoreElements()) {
							all.add(result.nextElement());
						}
					}
				}
			}

			Enumeration<URL> superResources = super.findResources(name);
			if (all.isEmpty()) {
				return superResources;
			}

			while (superResources.hasMoreElements()) {
				all.add(superResources.nextElement());
			}
			return Collections.enumeration(all);
		}
		finally {
			Thread.currentThread().setContextClassLoader(originalClassLoader);
		}
	}

	/**
	 * Sets whether this class loader will allow Apache Ant classes or resources to be found or loaded from its set of plug-in class loaders.
	 * 
	 * @param allowLoading
	 *            whether or not to allow the plug-in class loaders to load the Apache Ant classes or resources
	 */
	public void allowPluginClassLoadersToLoadAnt(boolean allowLoading) {
		fAllowPluginLoading = allowLoading;
	}

	public void setPluginContextClassloader(ClassLoader classLoader) {
		fContextClassloader = classLoader;
	}
}