本文实例讲述了java实现的二级联动菜单效果。分享给大家供大家参考，具体如下：
jsp代码：
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<%@ 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.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[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>
java代码：
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;
/***
*
* @author zdw
*
*/
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
{
}
}
xml代码：
<?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>
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