问下关于extjs的动态树的问题

var _root = new Ext.tree.AsyncTreeNode({
							text:'功能菜单',
							id:'root',
							loader:new Ext.tree.TreeLoader({     
            					dataUrl:'menuAction.action'
        					})
var index = new Ext.tree.TreePanel({
   root:_root,
   代码略......
})

String nodeId = request.getParameter("node");
	StringBuffer tree = new StringBuffer();
	if(nodeId.equals("root")){
		tree.append("[");
		tree.append("{id:'level1-1',text:'子节点1',leaf:true},");
		tree.append("{id:'level1-2',text:'节点目录2',leaf:false},");
		tree.append("{id:'level1-3',text:'节点目录3',leaf:false}");
		tree.append("]");
	}else if(nodeId.equals("level1-2")){
		tree.append("[");
		tree.append("{id:'level2-1',text:'二级节点2-1',leaf:true},");
		tree.append("{id:'level2-2',text:'二级节点2-2',leaf:true}");
		tree.append("]");
	}else{
		tree.append("[");
		tree.append("{id:'level3-1',text:'节点3-1',leaf:true},");
		tree.append("{id:'level3-2',text:'节点3-2',leaf:true}");
		tree.append("]");
	}
	response.getWriter().write(tree.toString());