Source for gnu.java.security.util.ExpirableObject

   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 this
  50:  * class will automatically be added to a {@link Timer} object that, once a
  51:  * timeout elapses, will automatically call the {@link Destroyable#destroy()}
  52:  * method.
  53:  * <p>
  54:  * Concrete subclasses must implement the {@link #doDestroy()} method instead of
  55:  * {@link Destroyable#destroy()}; the behavior of that method should match
  56:  * exactly the behavior desired of <code>destroy()</code>.
  57:  * <p>
  58:  * 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
  64:     implements Destroyable
  65: {
  66:   /**
  67:    * The default timeout, used in the default constructor.
  68:    */
  69:   public static final long DEFAULT_TIMEOUT = 3600000L;
  70: 
  71:   /**
  72:    * The timer that expires instances.
  73:    */
  74:   private static final Timer EXPIRER = new Timer(true);
  75: 
  76:   /**
  77:    * A reference to the task that will destroy this object when the timeout
  78:    * expires.
  79:    */
  80:   private final Destroyer destroyer;
  81: 
  82:   /**
  83:    * Create a new expirable object that will expire after one hour.
  84:    */
  85:   protected ExpirableObject()
  86:   {
  87:     this(DEFAULT_TIMEOUT);
  88:   }
  89: 
  90:   /**
  91:    * Create a new expirable object that will expire after the specified timeout.
  92:    *
  93:    * @param delay The delay before expiration.
  94:    * @throws IllegalArgumentException If <i>delay</i> is negative, or if
  95:    *           <code>delay + System.currentTimeMillis()</code> is negative.
  96:    */
  97:   protected ExpirableObject(final long delay)
  98:   {
  99:     destroyer = new Destroyer(this);
 100:     EXPIRER.schedule(destroyer, delay);
 101:   }
 102: 
 103:   /**
 104:    * Destroys this object. This method calls {@link #doDestroy}, then, if no
 105:    * exception is thrown, cancels the task that would destroy this object when
 106:    * the timeout is reached.
 107:    *
 108:    * @throws DestroyFailedException If this operation fails.
 109:    */
 110:   public final void destroy() throws DestroyFailedException
 111:   {
 112:     doDestroy();
 113:     destroyer.cancel();
 114:   }
 115: 
 116:   /**
 117:    * Subclasses must implement this method instead of the {@link
 118:    * Destroyable#destroy()} method.
 119:    *
 120:    * @throws DestroyFailedException If this operation fails.
 121:    */
 122:   protected abstract void doDestroy() throws DestroyFailedException;
 123: 
 124:   /**
 125:    * The task that destroys the target when the timeout elapses.
 126:    */
 127:   private final class Destroyer
 128:       extends TimerTask
 129:   {
 130:     private final ExpirableObject target;
 131: 
 132:     Destroyer(final ExpirableObject target)
 133:     {
 134:       super();
 135:       this.target = target;
 136:     }
 137: 
 138:     public void run()
 139:     {
 140:       try
 141:         {
 142:           if (! target.isDestroyed())
 143:             target.doDestroy();
 144:         }
 145:       catch (DestroyFailedException dfe)
 146:         {
 147:         }
 148:     }
 149:   }
 150: }