如何在JTree中只显示目录？

import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;

public class DirectoryTreeModel extends DefaultTreeModel {
    public DirectoryTreeModel(DefaultMutableTreeNode root) {
        super(root);
    }

    @Override
    public boolean isLeaf(Object node) {
        // 判断节点是否为叶子节点
        return false;
    }
}

import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.JTree;

public class Main {
    public static void main(String[] args) {
        DefaultMutableTreeNode root = new DefaultMutableTreeNode("根目录");

        // 添加目录节点
        DefaultMutableTreeNode dir1 = new DefaultMutableTreeNode("目录1");
        DefaultMutableTreeNode dir2 = new DefaultMutableTreeNode("目录2");
        root.add(dir1);
        root.add(dir2);

        // 添加文件节点
        DefaultMutableTreeNode file1 = new DefaultMutableTreeNode("文件1");
        DefaultMutableTreeNode file2 = new DefaultMutableTreeNode("文件2");
        dir1.add(file1);
        dir2.add(file2);

        // 创建JTree并设置TreeModel
        JTree tree = new JTree(new DirectoryTreeModel(root));

        // 显示JTree
        // ...
    }
}