libjava/java/security/GuardedObject.java

   1 /* GuardedObject.java -- An object protected by a Guard
   2    Copyright (C) 1998, 2002 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., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 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 package java.security;
  39
  40 import java.io.Serializable;
  41 import java.io.IOException;
  42 import java.io.ObjectOutputStream;
  43
  44 /**
  45  * This class is an object that is guarded by a <code>Guard</code> object.
  46  * The object that is being guarded is retrieved by a call to the only
  47  * method in this class - <code>getObject</code>.  That method returns the
  48  * guarded <code>Object</code> after first checking with the
  49  * <code>Guard</code>.  If the <code>Guard</code> disallows access, an
  50  * exception will be thrown.
  51  *
  52  * @author Aaron M. Renn <arenn@urbanophile.com>
  53  * @since 1.1
  54  * @status updated to 1.4
  55  */
  56 public class GuardedObject implements Serializable
  57 {
  58   /**
  59    * Compatible with JDK 1.1+.
  60    */
  61   private static final long serialVersionUID = -5240450096227834308L;
  62
  63   /**
  64    * This is the Guard that is protecting the object.
  65    *
  66    * @serial the guard
  67    */
  68   private final Guard guard;
  69
  70   /**
  71    * This is the object that is being guarded.
  72    *
  73    * @serial the protected object
  74    */
  75   private final Object object;
  76
  77   /**
  78    * This method initializes a new instance of <code>GuardedObject</code>
  79    * that protects the specified <code>Object</code> using the specified
  80    * <code>Guard</code>. A null guard means there are no restrictions on
  81    * accessing the object.
  82    *
  83    * @param object the <code>Object</code> to guard
  84    * @param guard the <code>Guard</code> that is protecting the object
  85    */
  86   public GuardedObject(Object object, Guard guard)
  87   {
  88     this.object = object;
  89     this.guard = guard;
  90   }
  91
  92   /**
  93    * This method first call the <code>checkGuard</code> method on the
  94    * <code>Guard</code> object protecting the guarded object.  If the
  95    * <code>Guard</code> disallows access, an exception is thrown, otherwise
  96    * the <code>Object</code> is returned.
  97    *
  98    * @return The object being guarded
  99    * @throws SecurityException if access is denied
 100    */
 101   public Object getObject()
 102   {
 103     if (guard != null)
 104       guard.checkGuard(object);
 105     return object;
 106   }
 107
 108   /**
 109    * Ensures that serialization is legal, by checking the guard.
 110    *
 111    * @param s the stream to write to
 112    * @throws IOException if the underlying stream fails
 113    */
 114   private void writeObject(ObjectOutputStream s) throws IOException
 115   {
 116     if (guard != null)
 117       guard.checkGuard(object);
 118     s.defaultWriteObject();
 119   }
 120 } // class GuardedObject