jtree 默认展开树的全部节点

    public static void expandTree(JTree tree) {
        TreeNode root = (TreeNode) tree.getModel().getRoot();
        expandAll(tree, new TreePath(root), true);
    }

  
    private static void expandAll(JTree tree, TreePath parent, boolean expand) {
        // Traverse children
        TreeNode node = (TreeNode) parent.getLastPathComponent();
        if (node.getChildCount() >= 0) {
            for (Enumeration e = node.children(); e.hasMoreElements(); ) {
                TreeNode n = (TreeNode) e.nextElement();
                TreePath path = parent.pathByAddingChild(n);
                expandAll(tree, path, expand);
            }
        }

        // Expansion or collapse must be done bottom-up
        if (expand) {
            tree.expandPath(parent);
        } else {
            tree.collapsePath(parent);
        }
    }