libjava/classpath/java/security/GuardedObject.java

   1 /* GuardedObject.java -- An object protected by a Guard
   2    Copyright (C) 1998, 2002, 2004, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.security;
  40
  41 import java.io.IOException;
  42 import java.io.ObjectOutputStream;
  43 import java.io.Serializable;
  44
  45 /**
  46  * This class is an object that is guarded by a <code>Guard</code> object.
  47  * The object that is being guarded is retrieved by a call to the only
  48  * method in this class - <code>getObject</code>.  That method returns the
  49  * guarded <code>Object</code> after first checking with the
  50  * <code>Guard</code>.  If the <code>Guard</code> disallows access, an
  51  * exception will be thrown.
  52  *
  53  * @author Aaron M. Renn (arenn@urbanophile.com)
  54  * @since 1.1
  55  * @status updated to 1.4
  56  */
  57 public class GuardedObject implements Serializable
  58 {
  59   /**
  60    * Compatible with JDK 1.1+.
  61    */
  62   private static final long serialVersionUID = -5240450096227834308L;
  63
  64   /**
  65    * This is the Guard that is protecting the object.
  66    *
  67    * @serial the guard
  68    */
  69   private final Guard guard;
  70
  71   /**
  72    * This is the object that is being guarded.
  73    *
  74    * @serial the protected object
  75    */
  76   private final Object object;
  77
  78   /**
  79    * This method initializes a new instance of <code>GuardedObject</code>
  80    * that protects the specified <code>Object</code> using the specified
  81    * <code>Guard</code>. A null guard means there are no restrictions on
  82    * accessing the object.
  83    *
  84    * @param object the <code>Object</code> to guard
  85    * @param guard the <code>Guard</code> that is protecting the object
  86    */
  87   public GuardedObject(Object object, Guard guard)
  88   {
  89     this.object = object;
  90     this.guard = guard;
  91   }
  92
  93   /**
  94    * This method first call the <code>checkGuard</code> method on the
  95    * <code>Guard</code> object protecting the guarded object.  If the
  96    * <code>Guard</code> disallows access, an exception is thrown, otherwise
  97    * the <code>Object</code> is returned.
  98    *
  99    * @return The object being guarded
 100    * @throws SecurityException if access is denied
 101    */
 102   public Object getObject()
 103   {
 104     if (guard != null)
 105       guard.checkGuard(object);
 106     return object;
 107   }
 108
 109   /**
 110    * Ensures that serialization is legal, by checking the guard.
 111    *
 112    * @param s the stream to write to
 113    * @throws IOException if the underlying stream fails
 114    */
 115   private void writeObject(ObjectOutputStream s) throws IOException
 116   {
 117     if (guard != null)
 118       guard.checkGuard(object);
 119     s.defaultWriteObject();
 120   }
 121 } // class GuardedObject