这个例子是实现省、市二级联动，当选择某一省时，改省下面的市就会在另一个下拉框显示出来。在本例中AJAX通过解析XML文件得到的数据传回到jsp页面，其中省市均是从数据库取到的值：
jsp页面代码：
<%@ 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>
</head>
<script type="text/javascript">
var xmlHttp=null;
//创建xmlhttprequest对象
if(window.XMLHttpRequest){
xmlHttp=new XMLHttpRequest();
}else{
xmlHttp=new ActiveObject("Microsoft.XMLHTTP");
}
var url="GetProvince?time="+new Date().getTime();
function getsheng(){
xmlHttp.open("post",url,true);
xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xmlHttp.send();
xmlHttp.onreadystatechange=getprovince;
}
function getprovince(){
if(xmlHttp.readyState==4 && xmlHttp.status==200){
var xmlFile=xmlHttp.responseXML;
//获取省的节点
var province=xmlFile.getElementsByTagName("province");;
//获取select标签
var pselect=document.getElementById("sheng");
//循环取出xml文件省信息
for(var i=0;i<province.length;i++){
var shorter=province[i].getAttribute("name");
var provincename=province[i].text;
//循环将省信息放入select中
pselect.options.add(new Option(provincename,shorter));//(text,value)
}
}
}
function getcity(){
xmlHttp.open("post",url,true);
xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
var province=document.getElementById("sheng").value;
alert("省："+province);
xmlHttp.send("province="+province);
xmlHttp.onreadystatechange=setcity;
}
function setcity(){
if(xmlHttp.readyState==4 && xmlHttp.status==200){
var city=document.getElementById("city");
var cityXml=xmlHttp.responseXML;
city.options.length=0;
var citys=cityXml.getElementsByTagName("city");
for(var i=0;i<citys.length;i++){
var cityname=citys[i].text;
alert(cityname);
city.options.add(new Option(cityname,cityname));
}
}
}
</script>
<body onload="getsheng()">
省：<select name="sheng" id="sheng" onchange="getcity()">
<option>请选择</option>
</select>
市：<select name="city" id="city">
</select>
</body>
</html>
servlet代码：
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
String province=request.getParameter("province");
if(province!=null){
sendCity(request,response,province);
}else{
ShengDao sd=new ShengDao();
List<Sheng> list=sd.selAll();
response.setCharacterEncoding("utf-8");
PrintWriter out=response.getWriter();
response.setContentType("text/xml");
out.println("<?xml version='1.0' encoding='UTF-8'?>");
out.println("<china>");
for (Sheng sheng : list) {
out.print("<province name='"+sheng.getShorter()+"'>"+sheng.getProvince()+"</province>");
out.println();
}
out.println("</china>");
}
}
public void sendCity(HttpServletRequest request, HttpServletResponse response,String shorter){
try {
request.setCharacterEncoding("utf-8");
} catch (UnsupportedEncodingException e1) {
e1.printStackTrace();
}
try {
response.setCharacterEncoding("utf-8");
PrintWriter out=response.getWriter();
response.setContentType("text/xml");
ShengDao sd=new ShengDao();
List<City> list=sd.selAll(shorter);
out.println("<?xml version='1.0' encoding='UTF-8'?>");
out.println("<province>");
for (City city : list) {
out.println("<city name='"+city.getShorter()+"'>"+city.getCityname()+"</city>");
System.out.println("<city name='"+city.getShorter()+"'>"+city.getCityname()+"</city>");
}
out.println("</province>");
} catch (IOException e) {
e.printStackTrace();
}
}