zTree异步加载时，点击父节点没有向后台取数据

 js代码：

		var curMenu = null, zTree_Menu = null;
		var setting = {
			async:{
				autoParam:["menuid"],//异步加载时自动提交父节点参数
				contentType:"application/json",//提交参数的数据类型
				enable:true,//是否开启异步加载模式
				type:"post",//提交方式
				url:"LoadServlet",//服务端加载类
			},
			view: {
				showLine: true,
				selectedMulti: false,
				dblClickExpand: false
			},
			data: {
				simpleData: {
					enable: true,
					idKey:"menuid",
					pIdKey:"parentid"
				}
			},
			callback:{
				asyncSuccess: zTreeOnAsyncSuccess,//异步加载成功的fun 
				asyncError: zTreeOnAsyncError, //加载错误的fun 
				beforeClick:beforeClick //捕获单击节点之前的事件回调函数 
			}
		};
		function zTreeOnAsyncError(event, treeId, treeNode){ alert("异步加载失败!"); } 
		function zTreeOnAsyncSuccess(event, treeId, treeNode, msg){ } 

		function beforeClick(treeId, node) {
			if (node.isParent) {
				if (node.level === 0) {
					var pNode = curMenu;
					while (pNode && pNode.level !==0) {
						pNode = pNode.getParentNode();
						alert(pNode);
					}
					if (pNode !== node) {
						var a = $("#" + pNode.tId + "_a");
						a.removeClass("cur");
						zTree_Menu.expandNode(pNode, false);
					}
					a = $("#" + node.tId + "_a");
					a.addClass("cur");

					var isOpen = false;
					for (var i=0,l=node.children.length; i<l; i++) {
						if(node.children[i].open) {
							isOpen = true;
							break;
						}
					}
					if (isOpen) {
						zTree_Menu.expandNode(node, true);
						curMenu = node;
					} else {
						zTree_Menu.expandNode(node.children[0].isParent?node.children[0]:node, true);
						curMenu = node.children[0];
					}
				} else {
					zTree_Menu.expandNode(node);
				}
			}
			return !node.isParent;
		}
		
		$(document).ready(function(){
			$.fn.zTree.init($("#treeDemo"), setting);
			zTree_Menu = $.fn.zTree.getZTreeObj("treeDemo");

		});

 

 

后台代码（LoadMenuDaoImpl）：

 conn=BaseDao.getConn();
   String sql="select * from tbl_menu where parentid=?";
   ps=conn.prepareStatement(sql);
   ps.setString(1, menuid);
   rs=ps.executeQuery();
   menu.append("[");
   while(rs.next()){
    menu.append("{menuid:'"+rs.getString("menuid")+"',parentid:'"+rs.getString("parentid")+"',name:'"+rs.getString("menuname")+"',isParent:true},");
   }
   menu.append("]");

 LoadMenuServlet代码：

 

response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		String menuid=request.getParameter("menuid");
		
		System.out.println(menuid);
		
		if(menuid==null||menuid.equals("")){
			menuid="0";
		}
		
		LoadMenuDao lmd=new LoadMenuDaoImpl();
		
		String menus=lmd.loadMenu(menuid);
		
		out.print(menus);
		
		out.flush();
		out.close();

 显示结果：

 

目前的问题是，菜单的根目录已经加载上来，但是，当我点击父节点的时候，如：数据展示篇，它并没有再次向后台读取数据！没有实现异步！

求解决！