| /* |
| * $Id$ |
| * |
| * Copyright 2006 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 org.apache.struts2.util; |
| |
| import java.io.IOException; |
| import java.io.InputStream; |
| import java.net.URL; |
| |
| |
| /** |
| * This class is extremely useful for loading resources and classes in a fault tolerant manner |
| * that works across different applications servers. |
| * <p/> |
| * It has come out of many months of frustrating use of multiple application servers at Atlassian, |
| * please don't change things unless you're sure they're not going to break in one server or another! |
| * |
| */ |
| public class ClassLoaderUtils { |
| |
| /** |
| * Load a given resource. |
| * <p/> |
| * This method will try to load the resource using the following methods (in order): |
| * <ul> |
| * <li>From {@link Thread#getContextClassLoader() Thread.currentThread().getContextClassLoader()} |
| * <li>From {@link Class#getClassLoader() ClassLoaderUtil.class.getClassLoader()} |
| * <li>From the {@link Class#getClassLoader() callingClass.getClassLoader() } |
| * </ul> |
| * |
| * @param resourceName The name of the resource to load |
| * @param callingClass The Class object of the calling object |
| */ |
| public static URL getResource(String resourceName, Class callingClass) { |
| URL url = null; |
| |
| url = Thread.currentThread().getContextClassLoader().getResource(resourceName); |
| |
| if (url == null) { |
| url = ClassLoaderUtils.class.getClassLoader().getResource(resourceName); |
| } |
| |
| if (url == null) { |
| url = callingClass.getClassLoader().getResource(resourceName); |
| } |
| |
| return url; |
| } |
| |
| /** |
| * This is a convenience method to load a resource as a stream. |
| * <p/> |
| * The algorithm used to find the resource is given in getResource() |
| * |
| * @param resourceName The name of the resource to load |
| * @param callingClass The Class object of the calling object |
| */ |
| public static InputStream getResourceAsStream(String resourceName, Class callingClass) { |
| URL url = getResource(resourceName, callingClass); |
| |
| try { |
| return (url != null) ? url.openStream() : null; |
| } catch (IOException e) { |
| return null; |
| } |
| } |
| |
| /** |
| * Load a class with a given name. |
| * <p/> |
| * It will try to load the class in the following order: |
| * <ul> |
| * <li>From {@link Thread#getContextClassLoader() Thread.currentThread().getContextClassLoader()} |
| * <li>Using the basic {@link Class#forName(java.lang.String) } |
| * <li>From {@link Class#getClassLoader() ClassLoaderUtil.class.getClassLoader()} |
| * <li>From the {@link Class#getClassLoader() callingClass.getClassLoader() } |
| * </ul> |
| * |
| * @param className The name of the class to load |
| * @param callingClass The Class object of the calling object |
| * @throws ClassNotFoundException If the class cannot be found anywhere. |
| */ |
| public static Class loadClass(String className, Class callingClass) throws ClassNotFoundException { |
| try { |
| return Thread.currentThread().getContextClassLoader().loadClass(className); |
| } catch (ClassNotFoundException e) { |
| try { |
| return Class.forName(className); |
| } catch (ClassNotFoundException ex) { |
| try { |
| return ClassLoaderUtils.class.getClassLoader().loadClass(className); |
| } catch (ClassNotFoundException exc) { |
| return callingClass.getClassLoader().loadClass(className); |
| } |
| } |
| } |
| } |
| |
| /** |
| * Prints the current classloader hierarchy - useful for debugging. |
| */ |
| public static void printClassLoader() { |
| System.out.println("ClassLoaderUtils.printClassLoader"); |
| printClassLoader(Thread.currentThread().getContextClassLoader()); |
| } |
| |
| /** |
| * Prints the classloader hierarchy from a given classloader - useful for debugging. |
| */ |
| public static void printClassLoader(ClassLoader cl) { |
| System.out.println("ClassLoaderUtils.printClassLoader(cl = " + cl + ")"); |
| |
| if (cl != null) { |
| printClassLoader(cl.getParent()); |
| } |
| } |
| } |