JavaScript之AJAX实现二级联动菜单(jsp+js+servlet+xml)

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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

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