/*

 * Copyright (c) 2006, 2011, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.misc;

/**

 * Provides utility functions related to URLClassLoaders or subclasses of it.

 *

 *                  W  A  R  N  I  N  G

 *

 * This class uses undocumented, unpublished, private data structures inside

 * java.net.URLClassLoader and sun.misc.URLClassPath.  Use with extreme caution.

 *

 * @author      tjquinn

 */

import java.io.IOException;

import java.net.URLClassLoader;

import java.util.*;

import java.util.jar.JarFile;

public class ClassLoaderUtil {

    /**

     * Releases resources held by a URLClassLoader. A new classloader must

     * be created before the underlying resources can be accessed again.

     * @param classLoader the instance of URLClassLoader (or a subclass)

     */

    public static void releaseLoader(URLClassLoader classLoader) {

        releaseLoader(classLoader, null);

    }

    /**

     * Releases resources held by a URLClassLoader.  Notably, close the jars

     * opened by the loader. Initializes and updates the List of

     * jars that have been successfully closed.

     * <p>

     * @param classLoader the instance of URLClassLoader (or a subclass)

     * @param jarsClosed a List of Strings that will contain the names of jars

     *  successfully closed; can be null if the caller does not need the information returned

     * @return a List of IOExceptions reporting jars that failed to close; null

     * indicates that an error other than an IOException occurred attempting to

     * release the loader; empty indicates a successful release; non-empty

     * indicates at least one error attempting to close an open jar.

     */

    public static List<IOException> releaseLoader(URLClassLoader classLoader, List<String> jarsClosed) {

        List<IOException> ioExceptions = new LinkedList<IOException>();

        try {

            /* Records all IOExceptions thrown while closing jar files. */

            if (jarsClosed != null) {

                jarsClosed.clear();

            }

            URLClassPath ucp = SharedSecrets.getJavaNetAccess()

                                                .getURLClassPath(classLoader);

            ArrayList<?> loaders = ucp.loaders;

            Stack<?> urls = ucp.urls;

            HashMap<?,?> lmap = ucp.lmap;

            /*

             *The urls variable in the URLClassPath object holds URLs that have not yet

             *been used to resolve a resource or load a class and, therefore, do

             *not yet have a loader associated with them.  Clear the stack so any

             *future requests that might incorrectly reach the loader cannot be

             *resolved and cannot open a jar file after we think we've closed

             *them all.

             */

            synchronized(urls) {

                urls.clear();

            }

            /*

             *Also clear the map of URLs to loaders so the class loader cannot use

             *previously-opened jar files - they are about to be closed.

             */

            synchronized(lmap) {

                lmap.clear();

            }

            /*

             *The URLClassPath object's path variable records the list of all URLs that are on

             *the URLClassPath's class path.  Leave that unchanged.  This might

             *help someone trying to debug why a released class loader is still used.

             *Because the stack and lmap are now clear, code that incorrectly uses a

             *the released class loader will trigger an exception if the

             *class or resource would have been resolved by the class

             *loader (and no other) if it had not been released.

             *

             *The list of URLs might provide some hints to the person as to where

             *in the code the class loader was set up, which might in turn suggest

             *where in the code the class loader needs to stop being used.

             *The URLClassPath does not use the path variable to open new jar

             *files - it uses the urls Stack for that - so leaving the path variable

             *will not by itself allow the class loader to continue handling requests.

             */

            /*

             *For each loader, close the jar file associated with that loader.

             *

             *The URLClassPath's use of loaders is sync-ed on the entire URLClassPath

             *object.

             */

            synchronized (ucp) {

                for (Object o : loaders) {

                    if (o != null) {

                        /*

                         *If the loader is a JarLoader inner class and its jarFile

                         *field is non-null then try to close that jar file.  Add

                         *it to the list of closed files if successful.

                         */

                        if (o instanceof URLClassPath.JarLoader) {

                                URLClassPath.JarLoader jl = (URLClassPath.JarLoader)o;

                                JarFile jarFile = jl.getJarFile();

                                try {

                                    if (jarFile != null) {

                                        jarFile.close();

                                        if (jarsClosed != null) {

                                            jarsClosed.add(jarFile.getName());

                                        }

                                    }

                                } catch (IOException ioe) {

                                    /*

                                     *Wrap the IOException to identify which jar

                                     *could not be closed and add it to the list

                                     *of IOExceptions to be returned to the caller.

                                     */

                                    String jarFileName = (jarFile == null) ? "filename not available":jarFile.getName();

                                    String msg = "Error closing JAR file: " + jarFileName;

                                    IOException newIOE = new IOException(msg);

                                    newIOE.initCause(ioe);

                                    ioExceptions.add(newIOE);

                                }

                        }

                    }

                }

                /*

                 *Now clear the loaders ArrayList.

                 */

                loaders.clear();

            }

        } catch (Throwable t) {

            throw new RuntimeException (t);

        }

        return ioExceptions;

    }

}