本篇文章为大家展示了使用Ajax怎么实现一个二级联动菜单，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。
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.οnlοad=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(); }else if(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("不能得到描述信息:" + req.statusText); } } } //解析返回xml的方法 function parseMessage(){ var xmlDoc = req.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 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.java
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;public class SelectServlet extends HttpServlet{ private static final long serialVersionUID = 1L; public SelectServlet() { super(); } public void destroy() { super.destroy(); } public void 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); // 获得请求中参数为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>"; } else if (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>"; } else if (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 {// 如果是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); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } public void 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>上述内容就是使用Ajax怎么实现一个二级联动菜单，你们学到知识或技能了吗？如果还想学到更多技能或者丰富自己的知识储备，欢迎关注编程网行业资讯频道。
