/*
 * 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,
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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 * This class uses undocumented, unpublished, private data structures inside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.
Params:
  • classLoader – the instance of URLClassLoader (or a subclass)
/** * 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.

Params:
  • classLoader – the instance of URLClassLoader (or a subclass)
  • 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
Returns: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.
/** * 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; } }