JTree Zustand speichern

Dieses Beispiel zeigt, wie wir den Zustand von einem JTree speichern können, so daß er nach einem Programmneustart wieder geladen werden kann, d.h. mit den Knoten so wie sie auf- oder zugeklappt waren, mit allen eventuell hinzugefügten Knoten, usw.

<code=java>/*

* TreeStatusDemo.java
* 
* This example shows you how to store the tree status with XMLEncoder
* so that it can be reloaded after program restart.
* Maybe it can help you.
*
* Btw, we can use XMLEncoder not only to store the tree status, but for storing any
* object we like. To do so, it's enough that the objects respect the "Bean" format,
* which is extremely simple:
*
* a public class where we add a default constructor (without parameters)
* and the setXXX and getXXX (or isXXX) methods for the properties.
* That's already all for it to work!
*/

import java.awt.*; import java.awt.event.*; import java.beans.*; import java.io.*; import java.util.*; import java.util.List; import javax.swing.*; import javax.swing.tree.*;

public class TreeStatusDemo extends JFrame {

   private JToolBar toolbar;
   private JButton btAdd;
   private JTree tree;
   private TreeModel model;
   private List<TreeNode[]> expanded;
   private int countNew;

   public TreeStatusDemo() {
       super("Tree Status Demo");
       setSize(400, 300);
       setLocationRelativeTo(null);
       setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);
       toolbar = new JToolBar();
       btAdd = new JButton("Add Node");
       tree = new JTree();
       toolbar.add(btAdd);
       getContentPane().add(toolbar, BorderLayout.NORTH);
       tree.setEditable(true);
       getContentPane().add(new JScrollPane(tree), BorderLayout.CENTER);
       try {
           deSerialize();
           restoreStatus();
       } catch (Exception e) {
       }
       model = tree.getModel();
       btAdd.addActionListener(new ActionListener() {

           public void actionPerformed(final ActionEvent evt) {
               addNode();
           }
       });
       addWindowListener(new WindowAdapter() {

           public void windowClosing(final WindowEvent e) {
               saveStatus();
               serialize();
               System.exit(0);
           }
       });
   }

   private void saveStatus() {
       //save the expanded Nodes:
       expanded = new ArrayList<TreeNode[]>();
       collectStatusInfo(model.getRoot());
   }

   private void restoreStatus() {
       //expand the saved Nodes:
       for (int i = expanded.size() - 1; i > -1; i--) {
           TreeNode[] ar = expanded.get(i);
           tree.expandPath(new TreePath(ar));
       }
   }

   private void collectStatusInfo(final Object o) {
       int cc = model.getChildCount(o);
       for (int i = 0; i < cc; i++) {
           DefaultMutableTreeNode child = (DefaultMutableTreeNode) model.getChild(o, i);
           TreeNode[] ar = child.getPath();
           if (!model.isLeaf(child) && tree.isExpanded(new TreePath(ar))) {
               expanded.add(ar);
               collectStatusInfo(child);
           }
       }
   }

   private void addNode() {
       TreePath selectedPath = tree.getSelectionPath();
       if (selectedPath == null) {
           return;
       }
       DefaultMutableTreeNode selectedNode = (DefaultMutableTreeNode) selectedPath.getLastPathComponent();
       DefaultMutableTreeNode newChild = new DefaultMutableTreeNode("new node " + countNew++);
       ((DefaultTreeModel) tree.getModel()).insertNodeInto(newChild, selectedNode, selectedNode.getChildCount());
       TreePath newPath = selectedPath.pathByAddingChild(newChild);
       tree.setSelectionPath(newPath);
       tree.startEditingAtPath(newPath);
   }

   public void serialize() {
       try {
           XMLEncoder o = new XMLEncoder(new BufferedOutputStream(new FileOutputStream("tree.xml")));
           o.writeObject(tree.getModel());
           o.writeObject(expanded);
           o.close();
       } catch (IOException e) {
           e.printStackTrace();
       }
   }

   @SuppressWarnings("unchecked")
   private void deSerialize() {
       try {
           XMLDecoder d = new XMLDecoder(new BufferedInputStream(new FileInputStream("tree.xml")));
           tree.setModel((TreeModel) d.readObject());
           expanded = (List<TreeNode[]>) d.readObject();
           d.close();
       } catch (FileNotFoundException ex) {
       }
   }

   public static void main(final String args[]) {
       SwingUtilities.invokeLater(new Runnable() {

           public void run() {
               new TreeStatusDemo().setVisible(true);
           }
       });
   }

}</code=java>