JTree简单的应用addTreeWillExpandListener

package com.kevin.treedemo.filesystem;import java.awt.BorderLayout;import javax.swing.JFrame;import javax.swing.JPanel;import javax.swing.JScrollPane;import javax.swing.JTree;import javax.swing.event.TreeExpansionEvent;import javax.swing.event.TreeWillExpandListener;import javax.swing.tree.DefaultMutableTreeNode;import javax.swing.tree.ExpandVetoException;import javax.swing.tree.TreePath;public class FileTree extends JPanel {/** *  */private static final long serialVersionUID = 1L;JTree tree = null;DefaultMutableTreeNode root = new DefaultMutableTreeNode("D");public FileTree() {setLayout(new BorderLayout(0, 0));tree = new JTree(root,true);JScrollPane scrollPane = new JScrollPane(tree);add(scrollPane, BorderLayout.CENTER);initTree();initTreeListener();}private void initTreeListener() {tree.addTreeWillExpandListener(new TreeWillExpandListener(){@Overridepublic void treeWillExpand(TreeExpansionEvent event)throws ExpandVetoException {TreePath o = event.getPath();DefaultMutableTreeNode node = (DefaultMutableTreeNode)o.getLastPathComponent();String file = node.toString();String[] files = FiltUtil.listDir("D:\\"+file);if(null == files){return;}for(String f:files){node.add(new DefaultMutableTreeNode(f,!FiltUtil.isFile("D:\\"+file+"\\"+f)));}//不能使用updateUI，否则会出现异常/*Exception in thread "AWT-EventQueue-0" java.lang.NullPointerExceptionat javax.swing.plaf.basic.BasicTreeUI.updateSize(BasicTreeUI.java:1801)at javax.swing.plaf.basic.BasicTreeUI.toggleExpandState(BasicTreeUI.java:2210)at javax.swing.plaf.basic.BasicTreeUI.handleExpandControlClick(BasicTreeUI.java:2196)at javax.swing.plaf.basic.BasicTreeUI.checkForClickInExpandControl(BasicTreeUI.java:2154)at javax.swing.plaf.basic.BasicTreeUI$Handler.handleSelection(BasicTreeUI.java:3508)at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressed(BasicTreeUI.java:3456)at java.awt.Component.processMouseEvent(Component.java:6035)at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)at java.awt.Component.processEvent(Component.java:5803)at java.awt.Container.processEvent(Container.java:2058)at java.awt.Component.dispatchEventImpl(Component.java:4410)at java.awt.Container.dispatchEventImpl(Container.java:2116)at java.awt.Component.dispatchEvent(Component.java:4240)at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3983)at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)at java.awt.Container.dispatchEventImpl(Container.java:2102)at java.awt.Window.dispatchEventImpl(Window.java:2429)at java.awt.Component.dispatchEvent(Component.java:4240)at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)at java.awt.EventDispatchThread.run(EventDispatchThread.java:121) *///tree.updateUI();}@Overridepublic void treeWillCollapse(TreeExpansionEvent event)throws ExpandVetoException {}});}private void initTree() {String [] files = FiltUtil.listDir("D:\\");for(String file:files){root.add(new DefaultMutableTreeNode(file,!FiltUtil.isFile("D:\\"+file)));}tree.updateUI();}public static void main(String[] args){JFrame f = new JFrame();f.setSize(500, 400);f.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);f.setContentPane(new FileTree());f.setVisible(true);}}

package com.kevin.treedemo.filesystem;import java.io.File;public class FiltUtil {public static String[] listDir(String path){File file = new File(path);if(file.isDirectory()){return file.list();} else {return null;}}public static boolean isFile(String path){File file = new File(path);return file.isFile();}}