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    1   /*
    2    * Copyright 2007 Sun Microsystems, Inc.  All Rights Reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Sun designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Sun in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
   22    * CA 95054 USA or visit www.sun.com if you need additional information or
   23    * have any questions.
   24    */
   25   
   26   package com.sun.tools.javac.file;
   27   
   28   import java.io.Closeable;
   29   import java.io.IOException;
   30   import java.lang.reflect.Field;
   31   import java.net.URL;
   32   import java.net.URLClassLoader;
   33   import java.util.ArrayList;
   34   import java.util.jar.JarFile;
   35   
   36   /**
   37    * A URLClassLoader that also implements Closeable.
   38    * Reflection is used to access internal data structures in the URLClassLoader,
   39    * since no public API exists for this purpose. Therefore this code is somewhat
   40    * fragile. Caveat emptor.
   41    * @throws Error if the internal data structures are not as expected.
   42    *
   43    *  <p><b>This is NOT part of any API supported by Sun Microsystems.  If
   44    *  you write code that depends on this, you do so at your own risk.
   45    *  This code and its internal interfaces are subject to change or
   46    *  deletion without notice.</b>
   47    */
   48   class CloseableURLClassLoader
   49           extends URLClassLoader implements Closeable {
   50       CloseableURLClassLoader(URL[] urls, ClassLoader parent) throws Error {
   51           super(urls, parent);
   52           try {
   53               getLoaders(); //proactive check that URLClassLoader is as expected
   54           } catch (Throwable t) {
   55               throw new Error("cannot create CloseableURLClassLoader", t);
   56           }
   57       }
   58   
   59       /**
   60        * Close any jar files that may have been opened by the class loader.
   61        * Reflection is used to access the jar files in the URLClassLoader's
   62        * internal data structures.
   63        * @throws java.io.IOException if the jar files cannot be found for any
   64        * reson, or if closing the jar file itself causes an IOException.
   65        */
   66       public void close() throws IOException {
   67           try {
   68               for (Object l: getLoaders()) {
   69                   if (l.getClass().getName().equals("sun.misc.URLClassPath$JarLoader")) {
   70                       Field jarField = l.getClass().getDeclaredField("jar");
   71                       JarFile jar = (JarFile) getField(l, jarField);
   72                       if (jar != null) {
   73                           //System.err.println("CloseableURLClassLoader: closing " + jar);
   74                           jar.close();
   75                       }
   76                   }
   77               }
   78           } catch (Throwable t) {
   79               IOException e = new IOException("cannot close class loader");
   80               e.initCause(t);
   81               throw e;
   82           }
   83       }
   84   
   85       private ArrayList<?> getLoaders()
   86               throws NoSuchFieldException, IllegalArgumentException, IllegalAccessException
   87       {
   88           Field ucpField = URLClassLoader.class.getDeclaredField("ucp");
   89           Object urlClassPath = getField(this, ucpField);
   90           if (urlClassPath == null)
   91               throw new AssertionError("urlClassPath not set in URLClassLoader");
   92           Field loadersField = urlClassPath.getClass().getDeclaredField("loaders");
   93           return (ArrayList<?>) getField(urlClassPath, loadersField);
   94       }
   95   
   96       private Object getField(Object o, Field f)
   97               throws IllegalArgumentException, IllegalAccessException {
   98           boolean prev = f.isAccessible();
   99           try {
  100               f.setAccessible(true);
  101               return f.get(o);
  102           } finally {
  103               f.setAccessible(prev);
  104           }
  105       }
  106   
  107   }

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