001    /* GuardedObject.java -- An object protected by a Guard
002       Copyright (C) 1998, 2002, 2004, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package java.security;
040    
041    import java.io.IOException;
042    import java.io.ObjectOutputStream;
043    import java.io.Serializable;
044    
045    /**
046     * This class is an object that is guarded by a <code>Guard</code> object.
047     * The object that is being guarded is retrieved by a call to the only
048     * method in this class - <code>getObject</code>.  That method returns the
049     * guarded <code>Object</code> after first checking with the
050     * <code>Guard</code>.  If the <code>Guard</code> disallows access, an
051     * exception will be thrown.
052     *
053     * @author Aaron M. Renn (arenn@urbanophile.com)
054     * @since 1.1
055     * @status updated to 1.4
056     */
057    public class GuardedObject implements Serializable
058    {
059      /**
060       * Compatible with JDK 1.1+.
061       */
062      private static final long serialVersionUID = -5240450096227834308L;
063    
064      /**
065       * This is the Guard that is protecting the object.
066       *
067       * @serial the guard
068       */
069      private final Guard guard;
070    
071      /**
072       * This is the object that is being guarded.
073       *
074       * @serial the protected object
075       */
076      private final Object object;
077    
078      /**
079       * This method initializes a new instance of <code>GuardedObject</code>
080       * that protects the specified <code>Object</code> using the specified
081       * <code>Guard</code>. A null guard means there are no restrictions on
082       * accessing the object.
083       *
084       * @param object the <code>Object</code> to guard
085       * @param guard the <code>Guard</code> that is protecting the object
086       */
087      public GuardedObject(Object object, Guard guard)
088      {
089        this.object = object;
090        this.guard = guard;
091      }
092    
093      /**
094       * This method first call the <code>checkGuard</code> method on the
095       * <code>Guard</code> object protecting the guarded object.  If the
096       * <code>Guard</code> disallows access, an exception is thrown, otherwise
097       * the <code>Object</code> is returned.
098       *
099       * @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