Ajax二级联动菜单实现原理及代码

作者: 阳光与卜鹰
来源: 51数据库
2021-08-18

index.jsp:

复制代码代码如下:

 
<%@ page language="java" pageencoding="utf-8"%> 
<html> 
<head> 
<title>二级菜单联动演示</title> 
<script type="text/javascript"> 
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> 

selectservlet:

复制代码代码如下:

 
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 
{ 
} 
} 

web.xml:

复制代码代码如下:

 
<?xml version="1.0" encoding="utf-8"?> 
<web-app version="2.4" xmlns="http://www.51sjk.com/Upload/Articles/1/0/267/267660_20210708021815759.jpg" 
xmlns:xsi="http://www.w3.org/2001/xmlschema-instance" 
xsi:schemalocation="http://www.51sjk.com/Upload/Articles/1/0/267/267660_20210708021815759.jpg 
http://www.51sjk.com/Upload/Articles/1/0/267/267660_20210708021815759.jpg/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> 