jQuery结合JSP实现省市区三级联动下拉菜单详解

<%@ 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%>"> 
 <title>省市区三级联动下拉菜单</title>
 <script type="text/javascript" src="<%=path %>/js/jquery/jquery-1.7.min.js"></script>
 <script type="text/javascript" src="<%=path %>/js/json/json-minified.js"></script>
 </head>
 <body>
 <table>
 <tr>
 <td>
 省份：
 <select name="province" id="province" onchange="onSelectChange(this,'city');"></select>
 城市：
 <select name="city" id="city" onchange="onSelectChange(this,'district');">
  <option value="">请选择</option>
 </select>
 区(县)：
 <select name="district" id="district">
  <option value="">请选择</option>
 </select>
 </td>
 </tr>
 </table>
 </body>
</html>
<script type="text/javascript">
function onSelectChange(obj,toSelId){
 setSelect(obj.value,toSelId);
}
function setSelect(fromSelVal,toSelId){
 //alert(document.getElementById("province").selectedIndex);
 document.getElementById(toSelId).innerHTML="";
 jQuery.ajax({
  url: "<%=path%>/getDropdownDataServlet",
  cache: false,
  data:"parentId="+fromSelVal,
  success: function(data){
  createSelectObj(data,toSelId);
  }
 });
}
function createSelectObj(data,toSelId){
 var arr = jsonParse(data);
 if(arr != null && arr.length>0){
  var obj = document.getElementById(toSelId);
  obj.innerHTML="";
  var nullOp = document.createElement("option");
  nullOp.setAttribute("value","");
  nullOp.appendChild(document.createTextNode("请选择"));
  obj.appendChild(nullOp);
  for(var o in arr){
   var op = document.createElement("option");
   op.setAttribute("value",arr[o].id);
   //op.text=arr[o].name;//这一句在ie下不起作用，用下面这一句或者innerHTML
   op.appendChild(document.createTextNode(arr[o].name));
   obj.appendChild(op);
  }
 }
}
setSelect('1','province');
</script>

public class GetDropdownDataServlet extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws IOException, ServletException {
  doPost(request, response);
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws IOException, ServletException {
  String parentId = request.getParameter("parentId");
  if (parentId == null || parentId == "") {
   parentId = "0";
  }
  Connection conn = null;
  String json = "";
  try {
   Class.forName("com.mysql.jdbc.Driver");
   conn = DriverManager.getConnection("jdbc:mysql://localhost/dropdown",
     "root", "root");
   Statement stat = conn.createStatement();
   ResultSet rs = stat
     .executeQuery("select region_id,region_name from region where parent_id = "
       + parentId);
   ArrayList rsList = new ArrayList();
   Map map = null;
   while (rs.next()) {
    map = new HashMap();
    map.put("id", rs.getInt(1));
    map.put("name", rs.getString(2));
    rsList.add(map);
   }
   rs = null;
   Gson gson = new Gson();
   json = gson.toJson(rsList);
   System.out.println("json=" + json);
  } catch (ClassNotFoundException e) {
   e.printStackTrace();
  } catch (SQLException e) {
   e.printStackTrace();
  } finally {
   if (conn != null) {
    try {
     conn.close();
    } catch (SQLException e) {
     e.printStackTrace();
    }
   }
  }
  response.setCharacterEncoding("UTF-8");
  response.getWriter().print(json);
 }
}