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ajax jsp二级联动下拉框 select框

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//==================>【index.jsp】===============================
<%@page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<% String path=request.getContextPath(); %>
<%@page import="com.sinoest.dfrf.orm.pojo.Mainmenu"%>
<%@page import="com.sinoest.dfrf.orm.pojo.Menucontent"%>
<% List<Mainmenu> mmlist = (List<Mainmenu>)request.getAttribute("mmList");
if(mmlist==null){ mmlist=new ArrayList(); } %>
<% List<Menucontent> mclist = (List<Menucontent>)request.getAttribute("mcList");
if(mclist==null){ mclist=new ArrayList(); } %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>二级菜单</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();
}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.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.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>
<select name="province" id="province" onChange="Change_Select()">
<!--第一个下拉菜单-->
<option value="0" selected>>>请选择</option>
<% for (int i = 0; i < mmlist.size(); i++) { Mainmenu mm = mmlist.get(i); %>
<option value="<%=mm.getId() %>"><%=mm.getName() %></option>
<%}%>
</select>
<select name="city" id="city">
<!--第二个下拉菜单-->
<option value="0">--请选择--</option>
</select>
</div>
</body>
</html>
//==================>【SelectServlet类】===============================
package com.sinoest.dfrf.common;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.sinoest.dfrf.menu.service.DaoHangService;
import com.sinoest.dfrf.orm.pojo.Menucontent;
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.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);
//---调用Service--------------------------------
DaoHangService dhs=new DaoHangService();
List<?> mclist=dhs.mcallId(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>";
}
if (targetId.equalsIgnoreCase(targetId))
{
for (int j = 0; j < mclist.size(); j++) {
Menucontent mc = (Menucontent) mclist.get(j);
xml += "<select><value>"+mc.getId()+"</value><text>"+mc.getContent()+"</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 http://java.sun.com/xml/ns/j2ee">http://java.sun.com/xml/ns/j2ee" xmlns:http://www.w3.org/2001/XMLSchema-instance">http://www.w3.org/2001/XMLSchema-instance" version="2.4" xsi:schemaLhttp://java.sun.com/xml/ns/j2ee">http://java.sun.com/xml/ns/j2eehttp://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet>
<servlet-name>SelectServlet</servlet-name>
<servlet-class>com.sinoest.dfrf.common.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>
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