libjava/classpath/gnu/java/security/util/ExpirableObject.java

   1 /* ExpirableObject.java -- an object that is automatically destroyed.
   2    Copyright (C) 2004, 2006 Free Software Foundation, Inc.
   3
   4 This file is a 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 of the License, or (at
   9 your option) 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; if not, write to the Free Software
  18 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
  19 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 gnu.java.security.util;
  40
  41 import java.util.Timer;
  42 import java.util.TimerTask;
  43
  44 import javax.security.auth.DestroyFailedException;
  45 import javax.security.auth.Destroyable;
  46
  47 /**
  48  * The base class for objects with sensitive data that are automatically
  49  * destroyed after a timeout elapses. On creation, an object that extends
  50  * this class will automatically be added to a {@link Timer} object that,
  51  * once a timeout elapses, will automatically call the {@link
  52  * Destroyable#destroy()} method.
  53  *
  54  * <p>Concrete subclasses must implement the {@link doDestroy()} method
  55  * instead of {@link Destroyable#destroy()}; the behavior of that method
  56  * should match exactly the behavior desired of <code>destroy()</code>.
  57  *
  58  * <p>Note that if a {@link DestroyFailedException} occurs when the timeout
  59  * expires, it will not be reported.
  60  *
  61  * @see Destroyable
  62  */
  63 public abstract class ExpirableObject implements Destroyable
  64 {
  65
  66   // Constants and fields.
  67   // -------------------------------------------------------------------------
  68
  69   /**
  70    * The default timeout, used in the default constructor.
  71    */
  72   public static final long DEFAULT_TIMEOUT = 3600000L;
  73
  74   /**
  75    * The timer that expires instances.
  76    */
  77   private static final Timer EXPIRER = new Timer(true);
  78
  79   /**
  80    * A reference to the task that will destroy this object when the timeout
  81    * expires.
  82    */
  83   private final Destroyer destroyer;
  84
  85   // Constructors.
  86   // -------------------------------------------------------------------------
  87
  88   /**
  89    * Create a new expirable object that will expire after one hour.
  90    */
  91   protected ExpirableObject()
  92   {
  93     this(DEFAULT_TIMEOUT);
  94   }
  95
  96   /**
  97    * Create a new expirable object that will expire after the specified
  98    * timeout.
  99    *
 100    * @param delay The delay before expiration.
 101    * @throws IllegalArgumentException If <i>delay</i> is negative, or if
 102    *  <code>delay + System.currentTimeMillis()</code> is negative.
 103    */
 104   protected ExpirableObject(final long delay)
 105   {
 106     destroyer = new Destroyer(this);
 107     EXPIRER.schedule(destroyer, delay);
 108   }
 109
 110   // Instance methods.
 111   // -------------------------------------------------------------------------
 112
 113   /**
 114    * Destroys this object. This method calls {@link doDestroy}, then, if
 115    * no exception is thrown, cancels the task that would destroy this object
 116    * when the timeout is reached.
 117    *
 118    * @throws DestroyFailedException If this operation fails.
 119    */
 120   public final void destroy() throws DestroyFailedException
 121   {
 122     doDestroy();
 123     destroyer.cancel();
 124   }
 125
 126   /**
 127    * Subclasses must implement this method instead of the {@link
 128    * Destroyable#destroy()} method.
 129    *
 130    * @throws DestroyFailedException If this operation fails.
 131    */
 132   protected abstract void doDestroy() throws DestroyFailedException;
 133
 134   // Inner classes.
 135   // -------------------------------------------------------------------------
 136
 137   /**
 138    * The task that destroys the target when the timeout elapses.
 139    */
 140   private final class Destroyer extends TimerTask
 141   {
 142
 143     // Fields.
 144     // -----------------------------------------------------------------------
 145
 146     private final ExpirableObject target;
 147
 148     // Constructor.
 149     // -----------------------------------------------------------------------
 150
 151     Destroyer(final ExpirableObject target)
 152     {
 153       super();
 154       this.target = target;
 155     }
 156
 157     // Instance methods.
 158     // -----------------------------------------------------------------------
 159
 160     public void run()
 161     {
 162       try
 163         {
 164           if (!target.isDestroyed())
 165             target.doDestroy();
 166         }
 167       catch (DestroyFailedException dfe)
 168         {
 169         }
 170     }
 171   }
 172 }