Java tutorial
/* * Copyright 1999-2005 The Apache Software Foundation. * * Licensed 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 com.meyling.telnet.startup; import java.net.URL; import java.lang.IllegalAccessException; import java.lang.reflect.Method; import java.lang.reflect.InvocationTargetException; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import com.meyling.telnet.shell.PwtsShell; /** Load resources (or images) from various sources. @author Ceki Gülcü (Very small adaptations by Michael Meyling.) */ public class Loader { static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous."; /** Trace logger. */ private static Log trace = LogFactory.getLog(PwtsShell.class); // We conservatively assume that we are running under Java 1.x static private boolean java1 = true; static private boolean ignoreTCL = false; static { String prop = System.getProperty("java.version", null); if (prop != null) { int i = prop.indexOf('.'); if (i != -1) { if (prop.charAt(i + 1) != '1') java1 = false; } } String ignoreTCLProp = System.getProperty("log4j.ignoreTCL", null); if (ignoreTCLProp != null) { ignoreTCL = toBoolean(ignoreTCLProp, true); } } /** * Get a resource by delegating to getResource(String). * @param resource resource name * @param clazz class, ignored. * @return URL to resource or null. * @deprecated as of 1.2. */ public static URL getResource(String resource, Class clazz) { return getResource(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 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>). Under JDK 1.1, only the the class loader that loaded this class (<code>Loader</code>) is used. <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> */ static public URL getResource(String resource) { ClassLoader classLoader = null; URL url = null; try { if (!java1) { classLoader = getTCL(); if (classLoader != null) { trace.debug("Trying to find [" + resource + "] using context classloader " + classLoader + "."); url = classLoader.getResource(resource); if (url != null) { return url; } } } // We could not find resource. Ler us now try with the // classloader that loaded this class. classLoader = Loader.class.getClassLoader(); if (classLoader != null) { trace.debug("Trying to find [" + resource + "] using " + classLoader + " class loader."); url = classLoader.getResource(resource); if (url != null) { return url; } } } catch (Throwable t) { trace.warn(TSTR, 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. trace.debug("Trying to find [" + resource + "] using ClassLoader.getSystemResource()."); return ClassLoader.getSystemResource(resource); } /** Are we running under JDK 1.x? */ public static boolean isJava1() { return java1; } /** * Get the Thread Context Loader which is a JDK 1.2 feature. If we * are running under JDK 1.1 or anything else goes wrong the method * returns <code>null<code>. * * */ private static ClassLoader getTCL() throws IllegalAccessException, InvocationTargetException { // Are we running on a JDK 1.2 or later system? Method method = null; try { method = Thread.class.getMethod("getContextClassLoader", null); } catch (NoSuchMethodException e) { // We are running on JDK 1.1 return null; } return (ClassLoader) method.invoke(Thread.currentThread(), null); } /** * If running under JDK 1.2 load the specified class using the * <code>Thread</code> <code>contextClassLoader</code> if that * fails try Class.forname. Under JDK 1.1 only Class.forName is * used. * */ static public Class loadClass(String clazz) throws ClassNotFoundException { // Just call Class.forName(clazz) if we are running under JDK 1.1 // or if we are instructed to ignore the TCL. if (java1 || ignoreTCL) { return Class.forName(clazz); } else { try { return getTCL().loadClass(clazz); } catch (Throwable 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); } } } /** If <code>value</code> is "true", then <code>true</code> is returned. If <code>value</code> is "false", then <code>true</code> is returned. Otherwise, <code>default</code> is returned. <p>Case of value is unimportant. */ public static boolean toBoolean(String value, boolean dEfault) { if (value == null) return dEfault; String trimmedVal = value.trim(); if ("true".equalsIgnoreCase(trimmedVal)) return true; if ("false".equalsIgnoreCase(trimmedVal)) return false; return dEfault; } }