guardedobject.java

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/* GuardedObject.java -- An object protected by a Guard
   Copyright (C) 1998, 2002 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package java.security;

import java.io.Serializable;
import java.io.IOException;
import java.io.ObjectOutputStream;

/**
 * This class is an object that is guarded by a <code>Guard</code> object.
 * The object that is being guarded is retrieved by a call to the only
 * method in this class - <code>getObject</code>.  That method returns the
 * guarded <code>Object</code> after first checking with the
 * <code>Guard</code>.  If the <code>Guard</code> disallows access, an
 * exception will be thrown.
 *
 * @author Aaron M. Renn <[e-mail]>
 * @since 1.1
 * @status updated to 1.4
 */
public class GuardedObject implements Serializable
{
  /**
   * Compatible with JDK 1.1+.
   */
  private static final long serialVersionUID = -5240450096227834308L;

  /**
   * This is the Guard that is protecting the object.
   *
   * @serial the guard
   */
  private final Guard guard;

  /**
   * This is the object that is being guarded.
   *
   * @serial the protected object
   */
  private final Object object;

  /**
   * This method initializes a new instance of <code>GuardedObject</code>
   * that protects the specified <code>Object</code> using the specified
   * <code>Guard</code>. A null guard means there are no restrictions on
   * accessing the object.
   *
   * @param object the <code>Object</code> to guard
   * @param guard the <code>Guard</code> that is protecting the object
   */
  public GuardedObject(Object object, Guard guard)
  {
    this.object = object;
    this.guard = guard;
  }

  /**
   * This method first call the <code>checkGuard</code> method on the
   * <code>Guard</code> object protecting the guarded object.  If the
   * <code>Guard</code> disallows access, an exception is thrown, otherwise
   * the <code>Object</code> is returned.
   *
   * @return The object being guarded
   * @throws SecurityException if access is denied
   */
  public Object getObject()
  {
    if (guard != null)
      guard.checkGuard(object);
    return object;
  }

  /**
   * Ensures that serialization is legal, by checking the guard.
   *
   * @param s the stream to write to
   * @throws IOException if the underlying stream fails
   */
  private void writeObject(ObjectOutputStream s) throws IOException
  {
    if (guard != null)
      guard.checkGuard(object);
    s.defaultWriteObject();
  }
} // class GuardedObject