001/* java.beans.PersistenceDelegate
002   Copyright (C) 2005 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038package 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 */
052public 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}