1、首先给出实现此功能的项目文件部署图（MyEclipse上实现）
2、实现三个文件
2.1、index.jsp源码如下：
<%@ page language="java" pageEncoding="UTF-8"%>
<html>
<head>
<title>二级菜单联动演示</title>
<script type="text/javascript" src="js/1.js"></script>
</head>
<body>
<div align="center">
<h1>二级联动示例 </h1>
<!--第一个下拉菜单-->
<select name="province" id="province" onChange="changeSelect()">
<option value="0"> 请选择武侠大师 </option>
<option value="1"> 金庸</option>
<option value="2"> 古龙 </option>
<option value="3"> 梁羽生</option>
</select>
<!--第二个下拉菜单-->
<select name="city" id="city">
<option value="0"> 请选择大师作品</option>
</select>
</div>
</body>
</html>
2.2、1.js文件源码如下：
var xhr;
//根据不同浏览器创建xhr对象的函数
function creatXHR () {
if (typeof(XMLHttpRequest)!="undefined") {
return new XMLHttpRequest(); //针对IE7及四大浏览器
}else if (typeof ActiveXObject !="undefined") {
if (typeof arguments.callee.activeXString!="string") {
var versions=["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"];
for (var i=0,len=versions.length;i<len;i++) {
try{
var xhr = new ActiveXObject(versions[i]);//针对IE7以下版本
arguments.callee.activeXString=versions[i];
return xhr;
}catch(e){
//TODO handle the exception
}
}
}
return new ActiveXObject(arguments.callee.activeXString);
}else{
throw new Error("No XHR object available");
}
}
//当第一个下拉框的选项发生改变时调用该函数
function changeSelect(){
var province = document.getElementById('province').value;
var url = "select?id="+ encodeURI(province);
xhr=creatXHR();
if(xhr){
xhr.open("GET",url,true);
//指定回调函数为callback
xhr.onreadystatechange = callback;
xhr.send(null);
}
}
//回调函数
function callback(){
if (xhr.readyState==4) {
if ((xhr.status>=200&&xhr.status<300)||xhr.status==304) {
parseMessage();
}else{
alert("Request was unsuccessful:"+xhr.status);
}
}
}
//解析返回xml的函数
function parseMessage(){
var xmlDoc = xhr.responseXML.documentElement;//获得返回的XML文档
var xSel = xmlDoc.getElementsByTagName('select'); //获得XML文档中的所有<select>标记
var select_root = document.getElementById('city'); //获得网页中的第二个下拉框
select_root.options.length=0; //每次获得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; //获得每个<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; //获得每个<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标记的值创建一个option对象
select_root.add(option);//将option对象添加到第二个下拉框中
}
}
2.3、SelectServlet.java文件源码
package Servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class SelectServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
request.setCharacterEncoding("GBK");
response.setCharacterEncoding("UTF-8");
String targetId = request.getParameter("id").toString(); //获得武侠大师编号
String xml_start = "<selects>";
String xml_end = "</selects>";
String xml = "";
if (targetId.equalsIgnoreCase("0"))
{
xml = "<select><value>0</value><text>请选择大师作品</text></select>";
} else if (targetId.equalsIgnoreCase("1"))
{
xml = "<select><value>1</value><text>射雕英雄传</text></select>";
xml += "<select><value>2</value><text>神雕侠侣</text></select>";
xml += "<select><value>3</value><text>天龙八部</text></select>";
xml += "<select><value>4</value><text>倚天屠龙记</text></select>";
} else if (targetId.equalsIgnoreCase("2"))
{
xml = "<select><value>1</value><text>小李飞刀</text></select>";
xml += "<select><value>2</value><text>飞刀问情</text></select>";
xml += "<select><value>3</value><text>飞刀又见飞刀</text></select>";
xml += "<select><value>4</value><text>萧十一郎</text></select>";
} else
{// 如果是3,则返回下面的字符
xml = "<select><value>1</value><text>云海玉弓缘</text></select>";
xml += "<select><value>2</value><text>萍踪侠影</text></select>";
xml += "<select><value>3</value><text>白发魔女传</text></select>";
xml += "<select><value>4</value><text>七剑下天山</text></select>";
}
String last_xml = xml_start + xml + xml_end;
response.getWriter().write(last_xml);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doGet(request, response);
}
}
3、效果图
