情况是这样的，
就像windows 里的我的电脑一样，当用资源管理器点击一个文件夹时，它下面的子文件夹显示出来，再点就缩回
但是我这里实现的
HTML code:
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<script type="text/javascript" src="js/jquery.js"></script>
<script type="text/javascript" src="js/menu.js"></script>
<link rel="stylesheet" type="text/css" href="css/css.css">
</head>
<body>
<div id="menus">
<div class="menu">
<span class="main"><a href="">主菜单项 1</a> </span>
<div class="subs">
<div class="sub">
<a href="">子菜单项</a>
