Preferences.exportSubTree() does not export all xml nodes

[Jon Camilleri]

The following code should write information to a preferences file, that is expected to include left, top, width, height, and, title nodes, however, it does not seem to happen. Any idea how to update the code so that preferences are included within the preferences file exported from the File > Export Preferences option?

import java.awt.EventQueue;
import java.awt.event.*;
import java.io.*;
import java.util.prefs.*;
import javax.swing.*;

/**
 * A program to test preference settings. The program remembers the frame position, size, and title.
 * @version 1.02 2007-06-12
 * @author Cay Horstmann
 */
public class PreferencesTest
{
   public static void main(String[] args)
   {
      EventQueue.invokeLater(new Runnable()
         {
            public void run()
            {
               PreferencesFrame frame = new PreferencesFrame();
               frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
               frame.setVisible(true);
            }
         });
   }
}

/**
 * A frame that restores position and size from user preferences and updates the preferences upon
 * exit.
 */
class PreferencesFrame extends JFrame
{
   public PreferencesFrame()
   {
      // get position, size, title from preferences

      Preferences root = Preferences.userRoot();
      final Preferences node = root.node("/com/horstmann/corejava");
      int left = node.getInt("left", 0);
      int top = node.getInt("top", 0);
      int width = node.getInt("width", DEFAULT_WIDTH);
      int height = node.getInt("height", DEFAULT_HEIGHT);
      setBounds(left, top, width, height);

      // if no title given, ask user

      String title = node.get("title", "");
      if (title.equals("")) title = JOptionPane.showInputDialog("Please supply a frame title:");
      if (title == null) title = "";
      setTitle(title);

      // set up file chooser that shows XML files

      final JFileChooser chooser = new JFileChooser();
      chooser.setCurrentDirectory(new File("."));

      // accept all files ending with .xml
      chooser.setFileFilter(new javax.swing.filechooser.FileFilter()
         {
            public boolean accept(File f)
            {
               return f.getName().toLowerCase().endsWith(".xml") || f.isDirectory();
            }

            public String getDescription()
            {
               return "XML files";
            }
         });

      // set up menus
      JMenuBar menuBar = new JMenuBar();
      setJMenuBar(menuBar);
      JMenu menu = new JMenu("File");
      menuBar.add(menu);

      JMenuItem exportItem = new JMenuItem("Export preferences");
      menu.add(exportItem);
      exportItem.addActionListener(new ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               if (chooser.showSaveDialog(PreferencesFrame.this) == JFileChooser.APPROVE_OPTION)
               {
                  try
                  {
                     OutputStream out = new FileOutputStream(chooser.getSelectedFile());
                     node.exportSubtree(out); //shouldn't this line export all the sub-nodes?
                     out.close();
                  }
                  catch (Exception e)
                  {
                     e.printStackTrace();
                  }
               }
            }
         });

      JMenuItem importItem = new JMenuItem("Import preferences");
      menu.add(importItem);
      importItem.addActionListener(new ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               if (chooser.showOpenDialog(PreferencesFrame.this) == JFileChooser.APPROVE_OPTION)
               {
                  try
                  {
                     InputStream in = new FileInputStream(chooser.getSelectedFile());
                     Preferences.importPreferences(in);
                     in.close();
                  }
                  catch (Exception e)
                  {
                     e.printStackTrace();
                  }
               }
            }
         });

      JMenuItem exitItem = new JMenuItem("Exit");
      menu.add(exitItem);
      exitItem.addActionListener(new ActionListener()
         {
            public void actionPerformed(ActionEvent event) //would it help to move this code within ActionEvent() for "Export preferences"?
            {
               node.putInt("left", getX());
               node.putInt("top", getY());
               node.putInt("width", getWidth());
               node.putInt("height", getHeight());
               node.put("title", getTitle());
               System.exit(0);
            }
         });
   }

   public static final int DEFAULT_WIDTH = 300;
   public static final int DEFAULT_HEIGHT = 200;
}

Source: Core Java Volume I (8th Edition) Listing 10-8 P. 546 to 549


preferences.xml - does not include nodes for left, top, width, height, and, title:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
<preferences EXTERNAL_XML_VERSION="1.0">
<root type="user">
<map/>
<node name="com">
<map/>
<node name="horstmann">
<map/>
<node name="corejava">
<map/>
</node>
</node>
</node>
</root>
</preferences>

"The actual storage of the data is dependent on the platform, e.g. under Windows the Windows Registry is used while under Linux a hidden file in the home directory of the user is used." Quoted from this article.

Does this code snippet save any entries in the Windows registry in my case? Can I look them up?

I am using Win XP SP3.