Source for gnu.java.beans.encoder.ClassPersistenceDelegate

   1: /* ClassPersistenceDelegate.java - A PersistenceDelegate for the Class type.
   2:    Copyright (C) 2005 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., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 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 gnu.java.beans.encoder;
  39: 
  40: import java.beans.Encoder;
  41: import java.beans.Expression;
  42: import java.beans.PersistenceDelegate;
  43: 
  44: /** <p>The <code>ClassPersistenceDelegate</code> creates
  45:  * <code>Expression</code> instances which denote class resolutions.</p>
  46:  *
  47:  * <p>The class resolution is always the last step when serializing a tree
  48:  * of objects. Due to the recursive nature of the algorithm we need a way
  49:  * to end the recursion. This is achieved by the implementation of this
  50:  * {@link instantiate} method. Arbitrary classes are described with a call
  51:  * to <code>Class.forName</code>. However for the <code>Class</code> class
  52:  * we call <code>getClass()</code> on a <code>String.class</code> instance.
  53:  * This in turn lead to the resolution of the String class which is always
  54:  * encoded as <code>"".getClass()</code>. Finally the <code>Encoder</code>
  55:  * treats strings in a special way so that the recursion ends here.
  56:  *
  57:  * @author Robert Schuster (robertschuster@fsfe.org)
  58:  */
  59: public class ClassPersistenceDelegate extends PersistenceDelegate
  60: {
  61: 
  62:   protected Expression instantiate(Object oldInstance, Encoder out)
  63:   {
  64:     Class oldClass = (Class) oldInstance;
  65: 
  66:     // Due to the special handling of String instances in the Encoder
  67:     // this Expression does not lead to further class resolutions.
  68:     if (oldClass == String.class)
  69:       return new Expression(oldClass, "", "getClass", null);
  70: 
  71:     // This Expression will lead to the class resolution of String.class.
  72:     if (oldClass == Class.class)
  73:       return new Expression(oldClass, String.class, "getClass", null);
  74: 
  75:     // This Expression will lead to the class resolution of Class.class.
  76:     return new Expression(oldClass, Class.class, "forName",
  77:                           new Object[] { oldClass.getName() });
  78:   }
  79: 
  80: }