Ajax实现二级联动菜单

http://www.blogjava.net/supercrsky/articles/203698.html

index.jsp:

<% @ page language="java" pageEncoding="UTF-8" %>
< html >
< head >
< title >二级菜单联动演示 </ title >
< script type ="text/javascript" >
var req;
window.onload=function()
{//页面加载时的函数
}

function Change_Select(){//当第一个下拉框的选项发生改变时调用该函数
var province = document.getElementById('province').value;
var url ="select?id="+ escape(province);
if(window.XMLHttpRequest){
req =new XMLHttpRequest();
}elseif(window.ActiveXObject){
req =new ActiveXObject("Microsoft.XMLHTTP");
}
if(req){
req.open("GET",url,true);
//指定回调函数为callback
req.onreadystatechange = callback;
req.send(null);
}
}
//回调函数
function callback(){
if(req.readyState ==4){
if(req.status ==200){
parseMessage();//解析XML文档
}else{
alert("不能获得描述信息:"+ req.statusText);
}
}
}
//解析返回xml的方法
function parseMessage(){
var xmlDoc = req.responseXML.documentElement;//得到返回的XML文档
var xSel = xmlDoc.getElementsByTagName('select');
//得到XML文档中的全部<select>标记
var select_root = document.getElementById('city');
//得到网页中的第二个下拉框
select_root.options.length=0;
//每次得到新的数据的时候先把每二个下拉框架的长度清0

for(var i=0;i<xSel.length;i++){
var xValue = xSel[i].childNodes[0].firstChild.nodeValue;
//得到每一个<select>标记中的第一个标记的值,也就是<value>标记的值
var xText = xSel[i].childNodes[1].firstChild.nodeValue;
//得到每一个<select>标记中的第二个标记的值,也就是<text>标记的值

var option =new Option(xText, xValue);
//根据每组value和text标记的值建立一个option对象

try{
select_root.add(option);//将option对象添加到第二个下拉框中
}catch(e){
}
}
}
</ script >
</ head >

< body >
< div align ="center" >
< form name ="form1" method ="post" action ="" >
< table width ="70%" border ="0" cellspacing ="0" cellpadding ="0" >
< tr >
< td align ="center" >
二级联动示例
</ td >
</ tr >
< tr >
< td >
< select name ="province" id ="province" onChange ="Change_Select()" >
<!-- 第一个下拉菜单 -->
< option value ="0" >
请选择
</ option >
< option value ="1" >
北京
</ option >
< option value ="2" >
天津
</ option >
< option value ="3" >
山东
</ option >
</ select >
< select name ="city" id ="city" >
<!-- 第二个下拉菜单 -->
< option value ="0" >
请选择
</ option >
</ select >
</ td >
</ tr >
< tr >
< td >
</ td >
< tr >
</ table >
</ form >
</ div >
</ body >
</ html >

SelectServlet:

package com;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/** */ /***
*
* @author zdw
*
*/
public class SelectServlet extends HttpServlet
{

privatestaticfinallong serialVersionUID = 1L;

public SelectServlet()
{
super();
}

publicvoid destroy()
{
super.destroy();
}

publicvoid doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
// response.setCharacterEncoding("GBK");
response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
request.setCharacterEncoding("GBK");
response.setCharacterEncoding("UTF-8");
String targetId = request.getParameter("id").toString();
System.out.println(targetId);
// 得到请求中参数为id的值
String xml_start = "<selects>";
String xml_end = "</selects>";
String xml = "";

if (targetId.equalsIgnoreCase("0"))
{
xml = "<select><value>0</value><text>请选择</text></select>";
}elseif (targetId.equalsIgnoreCase("1"))
{
xml = "<select><value>1</value><text>昌平</text></select>";
xml += "<select><value>2</value><text>丰台</text></select>";
xml += "<select><value>3</value><text>海淀</text></select>";
xml += "<select><value>4</value><text>朝阳</text></select>";
}elseif (targetId.equalsIgnoreCase("2"))
{
xml = "<select><value>1</value><text>塘沽区</text></select>";
xml += "<select><value>2</value><text>汉沽区</text></select>";
xml += "<select><value>3</value><text>大港区</text></select>";
xml += "<select><value>4</value><text>东丽区</text></select>";
}else
{// 若是是3,则返回下面的字符
xml = "<select><value>1</value><text>济南</text></select>";
xml += "<select><value>2</value><text>青岛</text></select>";
xml += "<select><value>3</value><text>淄博</text></select>";
xml += "<select><value>4</value><text>枣庄</text></select>";
}

String last_xml = xml_start + xml + xml_end;
response.getWriter().write(last_xml);

}

publicvoid doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doGet(request, response);
}

publicvoid init() throws ServletException
{
}

}

web.xml:

<? xml version="1.0" encoding="UTF-8" ?>
< web-app version ="2.4" xmlns ="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation ="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" >
< servlet >
< servlet-name >SelectServlet </ servlet-name >
< servlet-class >com.SelectServlet </ servlet-class >
</ servlet >

< servlet-mapping >
< servlet-name >SelectServlet </ servlet-name >
< url-pattern >/select </ url-pattern >
</ servlet-mapping >
< welcome-file-list >
< welcome-file >index.jsp </ welcome-file >
</ welcome-file-list >
</ web-app >