Java tutorial
/*! * This program is free software; you can redistribute it and/or modify it under the * terms of the GNU Lesser General Public License, version 2.1 as published by the Free Software * Foundation. * * You should have received a copy of the GNU Lesser General Public License along with this * program; if not, you can obtain a copy at http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html * or from the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. * * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. * See the GNU Lesser General Public License for more details. * * Copyright (c) 2002-2013 Pentaho Corporation.. All rights reserved. */ package org.pentaho.platform.plugin.services.pluginmgr; import org.apache.commons.io.filefilter.WildcardFileFilter; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.pentaho.platform.engine.services.messages.Messages; import java.io.File; import java.io.FilenameFilter; import java.net.MalformedURLException; import java.net.URL; import java.net.URLClassLoader; import java.text.MessageFormat; import java.util.ArrayList; import java.util.List; /** * A custom implementation of {@link URLClassLoader} for Pentaho Platform Plugins. It is used to load plugin jars and * classes and aids in retrieving resources by providing a root directory to search for resources related to plugins. * <p> * Note: {@link PluginClassLoader} will search for jar files in a 'lib' subdirectory under the pluginDir provided in the * constructor. Class and other resources will be visible to this classloader in either the root directory of the plugin * or in the lib folder. * * @author aphillips */ public class PluginClassLoader extends URLClassLoader { private static Log log = LogFactory.getLog(PluginClassLoader.class); private File pluginDir; private boolean overrideLoad = false; /** * Creates a class loader for loading plugin classes and discovering resources. Jars must be located in * [pluginDir]/lib. * * @param pluginDir * the root directory of the plugin * @param parent * the parent classloader */ public PluginClassLoader(final File pluginDir, ClassLoader parent) { super(getPluginUrls(pluginDir), parent); this.pluginDir = pluginDir; if (log.isDebugEnabled()) { log.debug("URLs for this classloader:"); //$NON-NLS-1$ for (URL url : getURLs()) { log.debug(url); } } } /** * Convenience method that creates a {@link PluginClassLoader} with the current classloader as it's parent. * * @param pluginDir * the root directory of the plugin * @param o * the object from which the parent classloader will be derived */ public PluginClassLoader(final File pluginDir, Object o) { this(pluginDir, o.getClass().getClassLoader()); } /** * Controls whether or not this classloader will eagerly load a class requested by {@link #loadClass(String, boolean)} * ahead of the parent classloader. or delegate the load to the parent. If this method is not called, the default * behavior will apply which is to *not* override classloading. * * @param b * if true, loadClass method will look to this loader first to load a class, otherwise, the parent * classloader will be queried first. */ public void setOverrideLoad(boolean b) { overrideLoad = b; if (b) { log.debug("classloader " + this + " is set to override mode. loadClass will now attempt to load " //$NON-NLS-1$ //$NON-NLS-2$ + "the class from the classpath known to this classloader before delegating to the parent classloader"); //$NON-NLS-1$ } } protected static URL[] getPluginUrls(File pluginDir) { List<URL> urls = new ArrayList<URL>(); File libDir = new File(pluginDir, "lib"); //$NON-NLS-1$ try { urls.add(pluginDir.toURI().toURL()); urls.add(libDir.toURI().toURL()); } catch (MalformedURLException e) { log.warn(Messages.getInstance() .getString("PluginClassLoader.WARN_FAILED_TO_ADD_PLUGIN_DIR_TO_CLASSPATH", pluginDir //$NON-NLS-1$ .getAbsolutePath(), libDir.getAbsolutePath()), e); } addJars(urls, libDir); return urls.toArray(new URL[urls.size()]); } protected static void addJars(List<URL> urls, File folder) { if (folder.exists() && folder.isDirectory()) { // get a list of all the JAR files FilenameFilter filter = new WildcardFileFilter("*.jar"); //$NON-NLS-1$ File[] jarFiles = folder.listFiles(filter); if (jarFiles != null && jarFiles.length > 0) { for (File file : jarFiles) { URL url = null; try { url = file.toURI().toURL(); if (log.isDebugEnabled()) { log.debug("adding jar to plugin classloader: " + url.toString()); //$NON-NLS-1$ } urls.add(url); } catch (MalformedURLException e) { log.warn(MessageFormat.format("PluginClassLoader.WARN_FAILED_TO_ADD_JAR_TO_CLASSPATH", file //$NON-NLS-1$ .getAbsolutePath()), e); } } } } } public File getPluginDir() { return pluginDir; } @Override public Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException { if (log.isDebugEnabled()) { log.debug("loadClass(" + name + ")... "); //$NON-NLS-1$ //$NON-NLS-2$ } Class<?> t = null; /* * Here we check the cache to see if the class has been loaded before by either this or the parent classloader. If * it has, then there is no need to load the class again, just return it. */ t = findLoadedClass(name); if (t != null) { if (log.isDebugEnabled()) { log.debug(MessageFormat.format("{0} loaded by {1}", name, t.getClassLoader())); //$NON-NLS-1$ } return t; } /* * If we are overriding the parent classloader we will first try to load this class from this classloader object in * isolation (no awareness of the parent classloader). If this classloader does not have the class, we will proceed * to attempt to load the class from the parent. */ if (overrideLoad) { try { t = findClass(name); if (t != null) { if (log.isDebugEnabled()) { log.debug(MessageFormat.format("{0} loaded by {1}", name, this)); //$NON-NLS-1$ } if (resolve) { resolveClass(t); } return t; } } catch (ClassNotFoundException e) { if (log.isTraceEnabled()) { log.trace(MessageFormat.format("class {0} not found in loader {1}. Trying parent loader", name, //$NON-NLS-1$ this)); } } } /* * At this point we have not found the class either in the cache or in this classloader, so we need to ask the * parent. */ t = super.loadClass(name, resolve); if (log.isDebugEnabled()) { log.debug(MessageFormat.format("{0} loaded by {1}", name, t.getClassLoader())); //$NON-NLS-1$ } return t; } @Override public String toString() { return super.toString() + ((pluginDir != null) ? " at " + pluginDir.getAbsolutePath() : ""); //$NON-NLS-1$ //$NON-NLS-2$ } }