001    /* java.beans.PersistenceDelegate
002       Copyright (C) 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    package java.beans;
039    
040    /** <p>A <code>PersistenceDelegate</code> describes how a another object
041     * has to constructed and transformed in order to create a complete
042     * replicate.</p>
043     * 
044     * <p>For custom classes you will need to implement
045     * <code>PersistenceDelegate</code> in a way that is suitable for them.
046     * To make use of the implementation you have to register it with an
047     * {@link Encoder} using the {Encoder#setPersistenceDelegate} method.</p>
048     * 
049     * @author Robert Schuster (robertschuster@fsfe.org)
050     * @since 1.4
051     */
052    public abstract class PersistenceDelegate
053    {
054    
055      protected void initialize(Class<?> type, Object oldInstance,
056                                Object newInstance, Encoder out)
057      {
058        if (type != Object.class)
059          {
060            type = type.getSuperclass();
061    
062            PersistenceDelegate pd = out.getPersistenceDelegate(type);
063            
064            pd.initialize(type, oldInstance, newInstance, out);
065          }
066      }
067    
068      public void writeObject(Object oldInstance, Encoder out)
069      {
070        Object streamCandidate = out.get(oldInstance);
071    
072        if (mutatesTo(oldInstance, streamCandidate))
073          {
074            initialize(oldInstance.getClass(), oldInstance, streamCandidate, out);
075          }
076        else
077          {
078            out.remove(oldInstance);
079            out.writeExpression(instantiate(oldInstance, out));
080          }
081      }
082    
083      protected boolean mutatesTo(Object oldInstance, Object newInstance)
084      {
085        return (newInstance != null)
086               && oldInstance.getClass() == newInstance.getClass();
087      }
088    
089      protected abstract Expression instantiate(Object oldInstance, Encoder out);
090    }