Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */ package org.apache.ws.security.util; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import java.lang.reflect.InvocationTargetException; import java.net.URL; import java.security.AccessController; import java.security.PrivilegedAction; /** * Load resources (or images) from various sources. * <p/> * * @author Davanum Srinivas (dims@yahoo.com). */ public class Loader { private static Log log = LogFactory.getLog(Loader.class.getName()); /** * This method will search for <code>resource</code> in different * places. The search order is as follows: * <ol> * <p><li>Search for <code>resource</code> using the thread context * class loader under Java2. * <p><li>Try one last time with * <code>ClassLoader.getSystemResource(resource)</code>, that is is * using the system class loader in JDK 1.2 and virtual machine's * built-in class loader in JDK 1.1. * </ol> * <p/> * * @param resource * @return TODO */ public static URL getResource(String resource) { ClassLoader classLoader = null; URL url = null; try { classLoader = getTCL(); if (classLoader != null) { log.debug("Trying to find [" + resource + "] using " + classLoader + " class loader."); url = classLoader.getResource(resource); if (url != null) { return url; } } } catch (Throwable t) { log.warn("Caught Exception while in Loader.getResource. This may be innocuous.", t); } // Last ditch attempt: get the resource from the class path. It // may be the case that clazz was loaded by the Extension class // loader which the parent of the system class loader. Hence the // code below. log.debug("Trying to find [" + resource + "] using ClassLoader.getSystemResource()."); return ClassLoader.getSystemResource(resource); } /** * This method will search for <code>resource</code> in different * places. The search order is as follows: * <ol> * <p><li>Search for <code>resource</code> using the supplied class loader. * If that fails, search for <code>resource</code> using the thread context * class loader. * <p><li>Try one last time with * <code>ClassLoader.getSystemResource(resource)</code>, that is is * using the system class loader in JDK 1.2 and virtual machine's * built-in class loader in JDK 1.1. * </ol> * <p/> * * @param resource * @return TODO */ public static URL getResource(ClassLoader loader, String resource) { URL url = null; try { if (loader != null) { log.debug("Trying to find [" + resource + "] using " + loader + " class loader."); url = loader.getResource(resource); if (url != null) { return url; } } } catch (Throwable t) { log.warn("Caught Exception while in Loader.getResource. This may be innocuous.", t); } return getResource(resource); } /** * Get the Thread context class loader. * <p/> * * @return the Thread context class loader * @throws IllegalAccessException * @throws InvocationTargetException */ public static ClassLoader getTCL() throws IllegalAccessException, InvocationTargetException { return (ClassLoader) AccessController.doPrivileged(new PrivilegedAction() { public Object run() { return Thread.currentThread().getContextClassLoader(); } }); } /** * Get the class loader of the class argument * <p/> * * @return the class loader of the argument */ public static ClassLoader getClassLoader(final Class clazz) { return (ClassLoader) AccessController.doPrivileged(new PrivilegedAction() { public Object run() { return clazz.getClassLoader(); } }); } /** * Try the specified classloader and then fall back to the loadClass * <p/> * * @param loader * @param clazz * @return Class * @throws ClassNotFoundException */ public static Class loadClass(ClassLoader loader, String clazz) throws ClassNotFoundException { try { if (loader != null) { Class c = loader.loadClass(clazz); if (c != null) { return c; } } } catch (Throwable e) { log.warn(e.getMessage(), e); } return loadClass(clazz, true); } /** * If running under JDK 1.2 load the specified class using the * <code>Thread</code> <code>contextClassLoader</code> if that * fails try Class.forname. * <p/> * * @param clazz * @return TODO * @throws ClassNotFoundException */ public static Class loadClass(String clazz) throws ClassNotFoundException { return loadClass(clazz, true); } public static Class loadClass(String clazz, boolean warn) throws ClassNotFoundException { try { ClassLoader tcl = getTCL(); if (tcl != null) { Class c = tcl.loadClass(clazz); if (c != null) { return c; } } } catch (Throwable e) { if (warn) { log.warn(e.getMessage(), e); } else { log.debug(e.getMessage(), e); } } // we reached here because tcl was null or because of a // security exception, or because clazz could not be loaded... // In any case we now try one more time return Class.forName(clazz); } }