001    /* DefaultPersistenceDelegate.java
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    
039    package java.beans;
040    
041    import java.lang.reflect.InvocationTargetException;
042    import java.lang.reflect.Method;
043    
044    /** <p><code>DefaultPersistenceDelegate</code> is a {@link PersistenceDelegate}
045     * implementation that can be used to serialize objects which adhere to the
046     * Java Beans naming convention.</p>
047     * 
048     * @author Robert Schuster (robertschuster@fsfe.org)
049     * @since 1.4
050     */
051    public class DefaultPersistenceDelegate extends PersistenceDelegate
052    {
053    
054      private String[] constructorPropertyNames;
055    
056      /** Using this constructor the object to be serialized will be instantiated
057       * with the default non-argument constructor.
058       */
059      public DefaultPersistenceDelegate()
060      {
061      }
062    
063      /** This constructor allows to specify which Bean properties appear
064       * in the constructor.
065       * 
066       * <p>The implementation reads the mentioned properties from the Bean
067       * instance and applies it in the given order to a corresponding
068       * constructor.</p>
069       * 
070       * @param constructorPropertyNames The properties the Bean's constructor
071       * should be given to.
072       */
073      public DefaultPersistenceDelegate(String[] constructorPropertyNames)
074      {
075        this.constructorPropertyNames = constructorPropertyNames;
076      }
077    
078      protected boolean mutatesTo(Object oldInstance, Object newInstance)
079      {
080        try
081          {
082    
083            return (constructorPropertyNames != null
084                   && constructorPropertyNames.length > 0
085                   && oldInstance.getClass()
086                   .getDeclaredMethod("equals",
087                                      new Class[] { Object.class }) != null)
088                                      ? oldInstance.equals(newInstance)
089                                      : super.mutatesTo(oldInstance, newInstance);
090          }
091        catch (NoSuchMethodException nsme)
092          {
093            return super.mutatesTo(oldInstance, newInstance);
094          }
095      }
096    
097      protected Expression instantiate(Object oldInstance, Encoder out)
098      {
099        Object[] args = null;
100    
101        try
102          {
103            // If there are property names in the array, then we create
104            // a corresponding argument array and store every
105            // argument in it. To retrieve an argument object we have
106            // dig up the right property in the bean class' BeanInfo
107            // object.
108            // This is so costly in terms of execution time I better
109            // not think twice about it ...
110            if (constructorPropertyNames != null)
111              {
112                args = new Object[constructorPropertyNames.length];
113    
114                // Look up the properties of oldInstance's class to find matches for
115                // the
116                // names given in the constructor.
117                PropertyDescriptor[] propertyDescs = Introspector.getBeanInfo(
118                                                                              oldInstance.getClass()).getPropertyDescriptors();
119    
120                for (int i = 0; i < constructorPropertyNames.length; i++)
121                  {
122                    // Scan the property descriptions for a matching name.
123                    for (int j = 0; j < propertyDescs.length; j++)
124                      {
125                        if (propertyDescs[i].getName().equals(
126                                                              constructorPropertyNames[i]))
127                          {
128                            Method readMethod = propertyDescs[i].getReadMethod();
129    
130                            args[i] = readMethod.invoke(oldInstance);
131                          }
132                      }
133                  }
134              }
135    
136          }
137        catch (IllegalAccessException iae)
138          {
139            out.getExceptionListener().exceptionThrown(iae);
140          }
141        catch (IllegalArgumentException iarge)
142          {
143            out.getExceptionListener().exceptionThrown(iarge);
144          }
145        catch (InvocationTargetException ite)
146          {
147            out.getExceptionListener().exceptionThrown(ite);
148          }
149        catch (IntrospectionException ie)
150          {
151            out.getExceptionListener().exceptionThrown(ie);
152          }
153    
154        return new Expression(oldInstance, oldInstance.getClass(), "new", args);
155      }
156    
157      protected void initialize(Class<?> type, Object oldInstance,
158                                Object newInstance, Encoder out)
159      {
160        // Calling the supertype's implementation of initialize makes it
161        // possible that descendants of classes like AbstractHashMap
162        // or Hashtable are serialized correctly. This mechanism grounds on
163        // two other facts:
164        // * Each class which has not registered a special purpose
165        //   PersistenceDelegate is handled by a DefaultPersistenceDelegate
166        //   instance.
167        // * PersistenceDelegate.initialize() is implemented in a way that it
168        //   calls the initialize method of the superclass' persistence delegate.
169        super.initialize(type, oldInstance, newInstance, out);
170        
171        // Suppresses the writing of property setting statements when this delegate
172        // is not used for the exact instance type. By doing so the following code
173        // is called only once per object.
174        if (type != oldInstance.getClass())
175          return;
176        
177        try
178          {
179            PropertyDescriptor[] propertyDescs = Introspector.getBeanInfo(
180                                                                          oldInstance.getClass()).getPropertyDescriptors();
181    
182            for (int i = 0; i < propertyDescs.length; i++)
183              {
184                Method readMethod = propertyDescs[i].getReadMethod();
185                Method writeMethod = propertyDescs[i].getWriteMethod();
186    
187                if (readMethod != null && writeMethod != null)
188                  {
189                    Object oldValue = readMethod.invoke(oldInstance);
190    
191                    if (oldValue != null)
192                      out.writeStatement(new Statement(oldInstance,
193                                                       writeMethod.getName(),
194                                                       new Object[] { oldValue }));
195                  }
196              }
197          }
198        catch (IntrospectionException ie)
199          {
200            out.getExceptionListener().exceptionThrown(ie);
201          }
202        catch (IllegalAccessException iae)
203          {
204            out.getExceptionListener().exceptionThrown(iae);
205          }
206        catch (InvocationTargetException ite)
207          {
208            out.getExceptionListener().exceptionThrown(ite);
209          }
210      }
211    }