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.axis2.util; import org.apache.axis2.java.security.AccessController; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import java.io.InputStream; import java.lang.reflect.InvocationTargetException; import java.net.URL; import java.security.PrivilegedAction; /** * Loads resources (or images) from various sources. */ public class Loader { private static final Log log = LogFactory.getLog(Loader.class); /** * Searches 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. If that fails, search for * <code>resource</code> using the class loader that loaded this * class (<code>Loader</code>). * <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 Returns URL */ static public URL getResource(String resource) { ClassLoader classLoader = null; URL url = null; try { // We could not find resource. Ler us now try with the // classloader that loaded this class. 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 Extentsion 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); } /** * Gets the resource with the specified class loader. * * @param loader * @param resource * @return Returns URL. * @throws ClassNotFoundException */ static public URL getResource(ClassLoader loader, String resource) throws ClassNotFoundException { 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); } /** * Searches 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. If that fails, search for * <code>resource</code> using the class loader that loaded this * class (<code>Loader</code>). * <p><li>Try one last time with * <code>ClassLoader.getSystemResourceAsStream(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 Returns URL */ static public InputStream getResourceAsStream(String resource) { ClassLoader classLoader = null; try { // Let's try the Thread Context Class Loader classLoader = getTCL(); if (classLoader != null) { log.debug("Trying to find [" + resource + "] using " + classLoader + " class loader."); InputStream is = classLoader.getResourceAsStream(resource); if (is != null) { return is; } } } catch (Throwable t) { log.warn("Caught Exception while in Loader.getResourceAsStream. This may be innocuous.", t); } try { // We could not find resource. Ler us now try with the // classloader that loaded this class. classLoader = Loader.class.getClassLoader(); if (classLoader != null) { log.debug("Trying to find [" + resource + "] using " + classLoader + " class loader."); InputStream is = classLoader.getResourceAsStream(resource); if (is != null) { return is; } } } catch (Throwable t) { log.warn("Caught Exception while in Loader.getResourceAsStream. 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 Extentsion class // loader which the parent of the system class loader. Hence the // code below. log.debug("Trying to find [" + resource + "] using ClassLoader.getSystemResourceAsStream()."); return ClassLoader.getSystemResourceAsStream(resource); } /** * Gets the resource with the specified class loader. * * @param loader * @param resource * @return Returns URL. * @throws ClassNotFoundException */ static public InputStream getResourceAsStream(ClassLoader loader, String resource) throws ClassNotFoundException { try { if (loader != null) { log.debug("Trying to find [" + resource + "] using " + loader + " class loader."); InputStream is = loader.getResourceAsStream(resource); if (is != null) { return is; } } } catch (Throwable t) { log.warn("Caught Exception while in Loader.getResource. This may be innocuous.", t); } return getResourceAsStream(resource); } /** * Gets the thread context class loader. * * @return Returns ClassLoader. * @throws IllegalAccessException * @throws InvocationTargetException */ static private ClassLoader getTCL() throws IllegalAccessException, InvocationTargetException { return (ClassLoader) AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() { public ClassLoader run() { return Thread.currentThread().getContextClassLoader(); } }); } /** * Loads the specified classloader and then falls back to the loadClass. * * @param loader * @param clazz * @return Returns Class. * @throws ClassNotFoundException */ static public Class loadClass(ClassLoader loader, String clazz) throws ClassNotFoundException { try { if (loader != null) { Class c = loader.loadClass(clazz); if (c != null) { return c; } } } catch (UnsupportedClassVersionError e) { log.debug(e); throw e; } catch (Throwable e) { log.debug(e); } return loadClass(clazz); } /** * If running under JDK 1.2, loads the specified class using the * <code>Thread</code> <code>contextClassLoader</code> . If that * fails, try Class.forname. * <p/> * * @param clazz * @return Returns Class. * @throws ClassNotFoundException */ static public Class loadClass(String clazz) throws ClassNotFoundException { try { ClassLoader tcl = getTCL(); if (tcl != null) { Class c = tcl.loadClass(clazz); if (c != null) { return c; } } } catch (UnsupportedClassVersionError e) { log.debug(e); throw e; } catch (Throwable e) { log.debug(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); } }