13.2 首选项信息的保存

1 属性映射

Properties settings = new Properties();
settings.setProperty("width", "200");
settings.setProperty("title", "Hello, World!");

OutputStream out = new FileOutputStream("program.properties");
settings.store(out, "Program Properties");

InputStream in = new FileInputStream("program.properties");
settings.load(in);

import java.awt.EventQueue;
import java.awt.event.*;
import java.io.*;
import java.util.Properties;

import javax.swing.*;

/**
 * A program to test properties. The program remembers the frame position, size,
 * and title.
 * @version 1.01 2015-06-16
 * @author Cay Horstmann
 */
public class PropertiesTest
{
   public static void main(String[] args)
   {
      EventQueue.invokeLater(() -> {
         PropertiesFrame frame = new PropertiesFrame();
         frame.setVisible(true);
      });
   }
}

/**
 * A frame that restores position and size from a properties file and updates
 * the properties upon exit.
 */
class PropertiesFrame extends JFrame
{
   private static final int DEFAULT_WIDTH = 300;
   private static final int DEFAULT_HEIGHT = 200;

   private File propertiesFile;
   private Properties settings;

   public PropertiesFrame()
   {
      // get position, size, title from properties

      String userDir = System.getProperty("user.home");
      File propertiesDir = new File(userDir, ".corejava");
      if (!propertiesDir.exists()) propertiesDir.mkdir();
      propertiesFile = new File(propertiesDir, "program.properties");

      Properties defaultSettings = new Properties();
      defaultSettings.setProperty("left", "0");
      defaultSettings.setProperty("top", "0");
      defaultSettings.setProperty("width", "" + DEFAULT_WIDTH);
      defaultSettings.setProperty("height", "" + DEFAULT_HEIGHT);
      defaultSettings.setProperty("title", "");

      settings = new Properties(defaultSettings);

      if (propertiesFile.exists()) 
         try (InputStream in = new FileInputStream(propertiesFile))
         {         
            settings.load(in);
         }
         catch (IOException ex)
         {
            ex.printStackTrace();
         }

      int left = Integer.parseInt(settings.getProperty("left"));
      int top = Integer.parseInt(settings.getProperty("top"));
      int width = Integer.parseInt(settings.getProperty("width"));
      int height = Integer.parseInt(settings.getProperty("height"));
      setBounds(left, top, width, height);

      // if no title given, ask user

      String title = settings.getProperty("title");
      if (title.equals(""))
         title = JOptionPane.showInputDialog("Please supply a frame title:");
      if (title == null) title = "";
      setTitle(title);

      addWindowListener(new WindowAdapter()
      {
         public void windowClosing(WindowEvent event)
         {
            settings.setProperty("left", "" + getX());
            settings.setProperty("top", "" + getY());
            settings.setProperty("width", "" + getWidth());
            settings.setProperty("height", "" + getHeight());
            settings.setProperty("title", getTitle());
            try (OutputStream out = new FileOutputStream(propertiesFile))
            {
               settings.store(out, "Program Properties");
            }
            catch (IOException ex)
            {
               ex.printStackTrace();
            }
            System.exit(0);
         }
      });
   }
}

---

2 首选项API

import java.awt.*;
import java.io.*;
import java.util.prefs.*;

import javax.swing.*;
import javax.swing.filechooser.*;

/**
 * A program to test preference settings. The program remembers the frame
 * position, size, and title.
 * @version 1.03 2015-06-12
 * @author Cay Horstmann
 */
public class PreferencesTest
{
   public static void main(String[] args)
   {
      EventQueue.invokeLater(() -> {
         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
{
   private static final int DEFAULT_WIDTH = 300;
   private static final int DEFAULT_HEIGHT = 200;
   private Preferences root = Preferences.userRoot();
   private Preferences node = root.node("/com/horstmann/corejava");

   public PreferencesFrame()
   {
      // get position, size, title from preferences

      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("."));
      chooser.setFileFilter(new FileNameExtensionFilter("XML files", "xml"));

      // 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(event -> {
               if (chooser.showSaveDialog(PreferencesFrame.this) == JFileChooser.APPROVE_OPTION)
               {
                  try
                  {
                     savePreferences();
                     OutputStream out = new FileOutputStream(chooser
                           .getSelectedFile());
                     node.exportSubtree(out);
                     out.close();
                  }
                  catch (Exception e)
                  {
                     e.printStackTrace();
                  }
               }
            });

      JMenuItem importItem = new JMenuItem("Import preferences");
      menu.add(importItem);
      importItem
            .addActionListener(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(event -> {
         savePreferences();
         System.exit(0);
      });
   }

   public void savePreferences() 
   {
      node.putInt("left", getX());
      node.putInt("top", getY());
      node.putInt("width", getWidth());
      node.putInt("height", getHeight());
      node.put("title", getTitle());      
   }
}