adaptiveclassloader.java

这是一个法律事务所系统源码

/*
 * Copyright (c) 1997-1999 The Java Apache Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the Java Apache 
 *    Project for use in the Apache JServ servlet engine project
 *    <http://java.apache.org/>."
 *
 * 4. The names "Apache JServ", "Apache JServ Servlet Engine" and 
 *    "Java Apache Project" must not be used to endorse or promote products 
 *    derived from this software without prior written permission.
 *
 * 5. Products derived from this software may not be called "Apache JServ"
 *    nor may "Apache" nor "Apache JServ" appear in their names without 
 *    prior written permission of the Java Apache Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the Java Apache 
 *    Project for use in the Apache JServ servlet engine project
 *    <http://java.apache.org/>."
 *    
 * THIS SOFTWARE IS PROVIDED BY THE JAVA APACHE PROJECT "AS IS" AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE JAVA APACHE PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Java Apache Group. For more information
 * on the Java Apache Project and the Apache JServ Servlet Engine project,
 * please see <http://java.apache.org/>.
 *
 */

package org.apache.tomcat.loader;
//package org.apache.java.lang;

import java.io.*;
import java.lang.*;
import java.net.*;
import java.text.*;
import java.util.*;
import java.util.zip.*;
import java.security.*;

/**
 * A class loader that loads classes from directories and/or zip-format
 * file such as JAR file. It tracks the modification time of the classes
 * it loads to permit reloading through re-instantiation.
 * <P>
 * When the classloader reports its creator that one of the classes it
 * has loaded has changed on disk, it should discard the classloader
 * and create a new instance using <CODE>reinstantiate</CODE>.
 * The classes are then reloaded into the new classloader as required.
 *
 * <P>The classloader can also load resources, which are a means
 * for packaging application data such as images within a jar file
 * or directory.
 *
 * <P>The classloader always first tries to load classes and resources
 * from the system, and uses it's own path if that fails. This is also
 * done if an empty repository is passed at construction.
 *
 * <P><B>How autoreload works:</B></P>
 *
 * <P>The Java VM considers two classes the same if they have the same
 * fully-qualified name <B>and</B> if they were loaded from the same
 * <CODE>ClassLoader</CODE>.
 *
 * <P>There is no way for a classloader to 'undefine' a class once it
 * has been loaded.  However, the servlet engine can discard a
 * classloader and the classes it contains, causing the
 *
 * <P>The <CODE>JServServletManager</CODE> creates a new instance of
 * the classloader each time it detects that any of the loaded classes
 * have changed.
 *
 * <P>Before terminating, all servlets are destroyed.
 *
 * <P>According to the Java Language Specification (JLS), classes may
 * be garbage-collected when there are no longer any instances of that
 * class and the <CODE>java.lang.Class</CODE> object is finalizable.
 * It is intended that this be the case when a <CODE>JServClassLoader</CODE>
 * is discarded.
 *
 * <P>Many VM releases did not implement class garbage collection
 * properly.  In such a VM, the memory usage will continue to grow if
 * autoreloading is enable.  Running the VM with
 * <CODE>-verbosegc</CODE> (or the corresponding option for
 * non-Javasoft VMs) may give some debugging information.
 *
 * <P>It is important that the <CODE>destroy</CODE> method be
 * implemented properly, as servlets may be destroyed and
 * reinitialized several times in the life of a VM.
 *
 * @author Francis J. Lacoste
 * @author Martin Pool
 * @author Jim Heintz
 * @author <a href="mailto:[e-mail]">Stefano Mazzocchi</a>
 * @version $Revision: 1.9.2.2 $ $Date: 2000/11/16 22:04:42 $
 * @see java.lang.ClassLoader
 */
public class AdaptiveClassLoader extends ClassLoader {
    private static final int debug=0;
    
    /**
     * Instance of the SecurityManager installed.
     */
    static protected SecurityManager sm;

    /**
     * Generation counter, incremented for each classloader as they are
     * created.
     */
    static private int generationCounter = 0;

    /**
     * Generation number of the classloader, used to distinguish between
     * different instances.
     */
    private int generation;

    /**
     * Cache of the loaded classes. This contains ClassCacheEntry keyed
     * by class names.
     */
    protected Hashtable cache;

    /**
     * The classpath which this classloader searches for class definitions.
     * Each element of the vector should be either a directory, a .zip
     * file, or a .jar file.
     * <p>
     * It may be empty when only system classes are controlled.
     */
    protected Vector repository;

    /**
     * A parent class loader for delegation of finding a class definition.
     * JDK 1.2 contains parent class loaders as part of java.lang.ClassLoader, the parent
     * being passed to a constructor, and retreived with getParent() method. For JDK 1.1
     * compatibility, we'll duplicate the 1.2 private member var.
     */
    protected ClassLoader parent;
    
    /**
     * Private class used to maintain information about the classes that
     * we loaded.
     */
    private static class ClassCacheEntry {

        /**
         * The actual loaded class
         */
        Class loadedClass;

        /**
         * The file from which this class was loaded; or null if
         * it was loaded from the system.
         */
        File origin;

        /**
         * The time at which the class was loaded from the origin
         * file, in ms since the epoch.
         */
        long lastModified;

        /**
         * Check whether this class was loaded from the system.
         */
        public boolean isSystemClass() {
            return origin == null;
        }
    }
    
    //------------------------------------------------------- Constructors

    /**
     * Creates a new class loader that will load classes from specified
     * class repositories, delegating first to the passed parent for definitions.
     *
     * @param classRepository An set of File classes indicating
     *        directories and/or zip/jar files. It may be empty when
     *        only system classes are loaded.
     * @param theParent A containing class loader for initial delegation of class
     *        definition serach.
     * @throw java.lang.IllegalArgumentException if the objects contained
     *        in the vector are not a file instance or the file is not
     *        a valid directory or a zip/jar file.
     */
    public AdaptiveClassLoader() {
	// Create the cache of loaded classes
	cache = new Hashtable();
    }

    public void setRepository( Vector classRepository ) 
	throws IllegalArgumentException
    {
	// Verify that all the repository are valid.
	Enumeration e = classRepository.elements();
	while(e.hasMoreElements()) {
	    ClassRepository cp = (ClassRepository) e.nextElement();
	    File file;
            String[] files;
            int i;

            // Check to see if element is a File instance.
            try {
                file = cp.getFile();
            } catch (ClassCastException objectIsNotFile) {
                throw new IllegalArgumentException("Object " + cp
                    + "is not a valid \"File\" instance");
            }
	    //	    org.apache.java.io.XXX
            files=SimpleFileFilter.fileOrFiles(file);
            if (files!=null)
            {
                for (i=0;i<files.length;i++)
                {
                    file=new File(files[i]);
                    // Check to see if we have proper access.
                    if (!file.exists()) {
                        throw new IllegalArgumentException("Repository "
                        + file.getAbsolutePath() + " doesn't exist!");
                    } else if (!file.canRead()) {
                        throw new IllegalArgumentException(
                        "Do not have read access for file "
                        + file.getAbsolutePath());
                    }

                    // Check that it is a directory or zip/jar file
                    if (!(file.isDirectory() || isZipOrJarArchive(file))) {
                        throw new IllegalArgumentException(
                           file.getAbsolutePath()
                           + " is not a directory or zip/jar file"
                           + " or if it's a zip/jar file then it is corrupted.");
                    }
                }
            }
        }

        // Store the class repository for use
        this.repository = classRepository;

        // Increment and store generation counter
        this.generation = generationCounter++;
    }

    public void setParent( ClassLoader p ) {
	parent=p;
    }

    void log( String s ) {
	System.out.println("AdaptiveClassLoader: " + s );
    }
    
    //------------------------------------------------------- Methods

    /**
     * Test if a file is a ZIP or JAR archive.
     *
     * @param file the file to be tested.
     * @return true if the file is a ZIP/JAR archive, false otherwise.
     */
    private boolean isZipOrJarArchive(File file) {
        boolean isArchive = true;
        ZipFile zipFile = null;

        try {
            zipFile = new ZipFile(file);
        } catch (ZipException zipCurrupted) {
            isArchive = false;
        } catch (IOException anyIOError) {
            isArchive = false;
        } finally {
            if (zipFile != null) {
                try {
                    zipFile.close();
                } catch (IOException ignored) {}
            }
        }

        return isArchive;
    }

    /**
     * Check to see if a given class should be reloaded because of a
     * modification to the original class.
     *
     * @param className The name of the class to check for modification.
     */
    public synchronized boolean shouldReload(String classname) {
	return checkExpired( classname );
    }

    protected boolean checkExpired(String classname ) {
	ClassCacheEntry entry = (ClassCacheEntry) cache.get(classname);

        if (entry == null) {
            // class wasn't even loaded
            return false;
        } else if (entry.isSystemClass()) {
            // System classes cannot be reloaded
            return false;
        } else {
            return (entry.origin.lastModified() != entry.lastModified);
        
        }
    }

    /**
     * Check whether the classloader should be reinstantiated.
     * <P>
     * The classloader must be replaced if there is any class whose
        * origin file has changed since it was last loaded.
     */
    public synchronized boolean shouldReload() {

        // Check whether any class has changed
        Enumeration e = cache.elements();
        while (e.hasMoreElements()) {
            ClassCacheEntry entry = (ClassCacheEntry) e.nextElement();

	    if( entry.loadedClass==null )
		continue;
	    if( debug>5 )
		log( "cache entry: " + entry.loadedClass.getName());
	    if (entry.isSystemClass()) continue;
	    
            // XXX: Because we want the classloader to be an accurate
            // reflection of the contents of the repository, we also
            // reload if a class origin file is now missing.  This
            // probably makes things a bit more fragile, but is OK in
            // a servlet development situation. <[e-mail]>

            long msOrigin = entry.origin.lastModified();

            if (msOrigin == 0) {
                // class no longer exists
                return true;
            }

            if (msOrigin != entry.lastModified) {
                // class is modified
                return true;
            }
        }

        // No changes, no need to reload
        return false;
    }

    /**
     * Re-instantiate this class loader.
     * <p>
     * This method creates a new instance
     * of the class loader that will load classes form the same path
     * as this one.
     */
    public AdaptiveClassLoader reinstantiate() {
        AdaptiveClassLoader cl=new AdaptiveClassLoader();
	cl.setParent(parent); 
	cl.setRepository(repository);
	return cl;
    }

    //------------------------------------ Implementation of Classloader

    /*
     * XXX: The javadoc for java.lang.ClassLoader says that the
     * ClassLoader should cache classes so that it can handle repeated
     * requests for the same class.  On the other hand, the JLS seems
     * to imply that each classloader is only asked to load each class
     * once.  Is this a contradiction?
     *
     * Perhaps the second call only applies to classes which have been
     * garbage-collected?
     */

    /**
     * Resolves the specified name to a Class. The method loadClass()
     * is called by the virtual machine.  As an abstract method,
     * loadClass() must be defined in a subclass of ClassLoader.
     *
     * @param      name the name of the desired Class.
     * @param      resolve true if the Class needs to be resolved;
     *             false if the virtual machine just wants to determine
     *             whether the class exists or not
     * @return     the resulting Class.
     * @exception  ClassNotFoundException  if the class loader cannot
     *             find a the requested class.
     */
    protected synchronized Class loadClass(String name, boolean resolve)
        throws ClassNotFoundException
    {
        if( debug>0) log( "loadClass() " + name);