Copyright (c) 2000, 2013 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
    Tom Tromey (tromey@redhat.com) - patch for bug 40972
/*******************************************************************************
 * Copyright (c) 2000, 2013 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 * 
 * 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.
Params:
allowLoading – 
           whether or not to allow the plug-in class loaders to load the Apache Ant classes or resources/**
	 * 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;
	}
}