Java tutorial
// // ======================================================================== // Copyright (c) 1995-2013 Mort Bay Consulting Pty. Ltd. // ------------------------------------------------------------------------ // All rights reserved. This program and the accompanying materials // are made available under the terms of the Eclipse Public License v1.0 // and Apache License v2.0 which accompanies this distribution. // // The Eclipse Public License is available at // http://www.eclipse.org/legal/epl-v10.html // // The Apache License v2.0 is available at // http://www.opensource.org/licenses/apache2.0.php // // You may elect to redistribute this code under either of these licenses. // ======================================================================== // package org.ireland.jnetty.loader; import java.io.IOException; import java.net.URL; import java.net.URLClassLoader; import java.util.ArrayList; import java.util.Collections; import java.util.Enumeration; import java.util.List; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /* ------------------------------------------------------------ */ /** * ClassLoader for HttpContext. Specializes URLClassLoader with some utility and file mapping methods. * * This loader defaults to the 2.3 servlet spec behavior where non system classes are loaded from the classpath in * preference to the parent loader. Java2 compliant loading, where the parent loader always has priority, can be * selected with the {@link org.eclipse.jetty.webapp.WebAppContext#setParentLoaderPriority(boolean)} method and * influenced with {@link WebAppContext#isServerClass(String)} and {@link WebAppContext#isSystemClass(String)}. * * If no parent class loader is provided, then the current thread context classloader will be used. If that is null then * the classloader that loaded this class is used as the parent. * */ public class WebAppClassLoader extends URLClassLoader { private static final Log LOG = LogFactory.getLog(WebAppClassLoader.class); private static final boolean isDebugEnabled = LOG.isDebugEnabled(); //Default: SystemClassLoader private final ClassLoader _parent; private String _name = String.valueOf(hashCode()); /** * Should this class loader delegate to the parent class loader <strong>before</strong> searching its own * repositories (i.e. the usual Java2 delegation model)? If set to <code>false</code>, this class loader will search * its own repositories first, and delegate to the parent only if the class or resource is not found locally. Note * that the default, <code>false</code>, is the behavior called for by the servlet specification. */ protected boolean delegate = true; /* ------------------------------------------------------------ */ /** * Constructor. */ public WebAppClassLoader() throws IOException { this(null); } /* ------------------------------------------------------------ */ /** * Constructor. */ public WebAppClassLoader(ClassLoader parent) throws IOException { super(new URL[] {}, parent != null ? parent : (Thread.currentThread().getContextClassLoader() != null ? Thread.currentThread().getContextClassLoader() : (WebAppClassLoader.class.getClassLoader() != null ? WebAppClassLoader.class.getClassLoader() : ClassLoader.getSystemClassLoader()))); _parent = getParent(); if (_parent == null) throw new IllegalArgumentException("no parent classloader!"); } /* ------------------------------------------------------------ */ /** * @return the name of the classloader */ public String getName() { return _name; } /* ------------------------------------------------------------ */ /** * @param name * the name of the classloader */ public void setName(String name) { _name = name; } /* ------------------------------------------------------------ */ /** * @param classPath * Comma or semicolon separated path of filenames or URLs pointing to directories or jar files. * Directories should end with '/'. */ public void addClassPath(URL classPath) { addURL(classPath); } /* ------------------------------------------------------------ */ /** * Add elements to the class path for the context from the jar and zip files found in the specified resource. * * @param lib * the resource that contains the jar and/or zip files. */ public void addJar(URL jarFile) { addURL(jarFile); } /* ------------------------------------------------------------ */ @Override public Enumeration<URL> getResources(String name) throws IOException { List<URL> from_parent = toList(_parent.getResources(name)); List<URL> from_webapp = toList(this.findResources(name)); if (delegate) { from_parent.addAll(from_webapp); return Collections.enumeration(from_parent); } from_webapp.addAll(from_parent); return Collections.enumeration(from_webapp); } /* ------------------------------------------------------------ */ private List<URL> toList(Enumeration<URL> e) { if (e == null) return new ArrayList<URL>(); return Collections.list(e); } /* ------------------------------------------------------------ */ /** * Get a resource from the classloader * */ @Override public URL getResource(String name) { URL url = null; // (1) Delegate to parent if requested if (delegate) { url = _parent.getResource(name); if (url != null) { if (isDebugEnabled) LOG.debug(" --> Returning '" + url.toString() + "' from parent classloader: " + _parent); return (url); } } // (2) Search local resources url = this.findResource(name); if (url != null) { if (isDebugEnabled) LOG.debug(" --> Returning '" + url.toString() + "' from " + toString()); return (url); } // (3) Delegate to parent unconditionally if not already attempted if (!delegate) { url = _parent.getResource(name); if (url != null) { if (isDebugEnabled) LOG.debug(" --> Returning '" + url.toString() + "' from parent classloader: " + _parent); return (url); } } // (4) Resource was not found if (isDebugEnabled) LOG.debug(" --> Resource not found, returning null"); return (null); } /* ------------------------------------------------------------ */ @Override public Class<?> loadClass(String name) throws ClassNotFoundException { return loadClass(name, false); } /* ------------------------------------------------------------ */ @Override protected synchronized Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException { Class<?> clazz = loadClass0(name); if (clazz != null) { if (resolve) resolveClass(clazz); return (clazz); } throw new ClassNotFoundException(name); } /** * Load class but not resolve * @param name * @return * @throws ClassNotFoundException */ protected synchronized Class<?> loadClass0(String name) throws ClassNotFoundException { // (0) Check our previously loaded class cache Class<?> clazz = findLoadedClass(name); if (clazz != null) { //if (isDebugEnabled) LOG.debug(" Returning class from cache,class: "+clazz); return (clazz); } // (1) Delegate to our parent if requested if (delegate) { if (isDebugEnabled) LOG.debug(" Delegating to parent classloader1: " + _parent); ClassLoader loader = _parent; try { clazz = Class.forName(name, false, loader); if (clazz != null) { if (isDebugEnabled) LOG.debug(" Loaded class from parent,class: " + clazz); return (clazz); } } catch (ClassNotFoundException e) { // Ignore } } // (2) Search local resources if (isDebugEnabled) LOG.debug(" Searching local ClassPaths @ " + name); try { clazz = findClass(name); if (clazz != null) { if (isDebugEnabled) LOG.debug(" Loaded class from local ClassPaths,class: " + clazz); return (clazz); } } catch (ClassNotFoundException e) { // Ignore } // (3) Delegate to parent unconditionally if (!delegate) { if (isDebugEnabled) LOG.debug(" Delegating to parent classloader at end: " + _parent); ClassLoader loader = _parent; try { clazz = Class.forName(name, false, loader); if (clazz != null) { if (isDebugEnabled) LOG.debug(" Loaded class from parent,class: " + clazz); return (clazz); } } catch (ClassNotFoundException e) { // Ignore } } throw new ClassNotFoundException(name); } /* ------------------------------------------------------------ */ @Override public String toString() { return "WebAppClassLoader=" + _name + "@" + Long.toHexString(hashCode()); } }