正如MadProgrammer解释的那样，这是一个小型演示示例，其中显示了一个JTree，它在树在节点上扩展时动态加载数据（并带有漂亮的加载栏作为奖励）：
import java.awt.BorderLayout;import java.awt.Dimension;import java.beans.PropertyChangeEvent;import java.beans.PropertyChangeListener;import java.beans.Transient;import java.util.ArrayList;import java.util.List;import javax.swing.Jframe;import javax.swing.JProgressBar;import javax.swing.JScrollPane;import javax.swing.JTree;import javax.swing.SwingUtilities;import javax.swing.SwingWorker;import javax.swing.UIManager;import javax.swing.UnsupportedLookAndFeelException;import javax.swing.event.TreeExpansionEvent;import javax.swing.event.TreeWillExpandListener;import javax.swing.tree.DefaultMutableTreeNode;import javax.swing.tree.DefaultTreeModel;import javax.swing.tree.ExpandVetoException;import javax.swing.tree.MutableTreeNode;import javax.swing.tree.TreePath;public class TestJTree { public static class MyTreeNode extends DefaultMutableTreeNode { private boolean loaded = false; private int depth; private final int index; public MyTreeNode(int index, int depth) { this.index = index; this.depth = depth; add(new DefaultMutableTreeNode("Loading...", false)); setAllowsChildren(true); setUserObject("Child " + index + " at level " + depth); } private void setChildren(List<MyTreeNode> children) { removeAllChildren(); setAllowsChildren(children.size() > 0); for (MutableTreeNode node : children) { add(node); } loaded = true; } @Override public boolean isLeaf() { return false; } public void loadChildren(final DefaultTreeModel model, final PropertyChangeListener progressListener) { if (loaded) { return; } SwingWorker<List<MyTreeNode>, Void> worker = new SwingWorker<List<MyTreeNode>, Void>() { @Override protected List<MyTreeNode> doInBackground() throws Exception { // Here access database if needed setProgress(0); List<MyTreeNode> children = new ArrayList<TestJTree.MyTreeNode>(); if (depth < 5) { for (int i = 0; i < 5; i++) { // Simulate DB access time Thread.sleep(300); children.add(new MyTreeNode(i + 1, depth + 1)); setProgress((i + 1) * 20); } } else { Thread.sleep(1000); } setProgress(0); return children; } @Override protected void done() { try { setChildren(get()); model.nodeStructureChanged(MyTreeNode.this); } catch (Exception e) { e.printStackTrace(); // Notify user of error. } super.done(); } }; if (progressListener != null) { worker.getPropertyChangeSupport().addPropertyChangeListener("progress", progressListener); } worker.execute(); } } protected void initUI() { Jframe frame = new Jframe(TestJTree.class.getSimpleName()); frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE); MyTreeNode root = new MyTreeNode(1, 0); final DefaultTreeModel model = new DefaultTreeModel(root); final JProgressBar bar = new JProgressBar(); final PropertyChangeListener progressListener = new PropertyChangeListener() { @Override public void propertyChange(PropertyChangeEvent evt) { bar.setValue((Integer) evt.getNewValue()); } }; JTree tree = new JTree() { @Override @Transient public Dimension getPreferredSize() { Dimension preferredSize = super.getPreferredSize(); preferredSize.width = Math.max(400, preferredSize.width); preferredSize.height = Math.max(400, preferredSize.height); return preferredSize; } }; tree.setShowsRootHandles(true); tree.addTreeWillExpandListener(new TreeWillExpandListener() { @Override public void treeWillExpand(TreeExpansionEvent event) throws ExpandVetoException { TreePath path = event.getPath(); if (path.getLastPathComponent() instanceof MyTreeNode) { MyTreeNode node = (MyTreeNode) path.getLastPathComponent(); node.loadChildren(model, progressListener); } } @Override public void treeWillCollapse(TreeExpansionEvent event) throws ExpandVetoException { } }); tree.setModel(model); root.loadChildren(model, progressListener); frame.add(new JScrollPane(tree)); frame.add(bar, BorderLayout.SOUTH); frame.pack(); frame.setVisible(true); } public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); SwingUtilities.invokeLater(new Runnable() { @Override public void run() { new TestJTree().initUI(); } }); }}
