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Ajax中二級聯動菜單的實現原理是什么，相信很多沒有經驗的人對此束手無策，為此本文總結了問題出現的原因和解決方法，通過這篇文章希望你能解決這個問題。
index.jsp:
<%@ page language="java" pageEncoding="UTF-8"%>
<html>
<head>
<title>二級菜單聯動演示</title>
<script type="text/javascript">
var req;
window.onload=function()
{//頁面加載時的函數
}
function Change_Select(){//當第一個下拉框的選項發生改變時調用該函數
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);
//指定回調函數為callback
req.onreadystatechange = callback;
req.send(null);
}
}
//回調函數
function callback(){
if(req.readyState ==4){
if(req.status ==200){
parseMessage();//解析XML文檔
}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;//獲得返回的XML文檔
var xSel = xmlDoc.getElementsByTagName('select');
//獲得XML文檔中的所有<select>標記
var select_root = document.getElementById('city');
//獲得網頁中的第二個下拉框
select_root.options.length=0;
//每次獲得新的數據的時候先把每二個下拉框架的長度清0
for(var i=0;i<xSel.length;i++){
var xValue = xSel[i].childNodes[0].firstChild.nodeValue;
//獲得每個<select>標記中的第一個標記的值,也就是<value>標記的值
var xText = xSel[i].childNodes[1].firstChild.nodeValue;
//獲得每個<select>標記中的第二個標記的值,也就是<text>標記的值
var option = new Option(xText, xValue);
//根據每組value和text標記的值創建一個option對象
try{
select_root.add(option);//將option對象添加到第二個下拉框中
}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">
二級聯動示例
</td>
</tr>
<tr>
<td>
<select name="province" id="province" onChange="Change_Select()">
<!--第一個下拉菜單-->
<option value="0">
請選擇
</option>
<option value="1">
北京
</option>
<option value="2">
天津
</option>
<option value="3">
山東
</option>
</select>
<select name="city" id="city">
<!--第二個下拉菜單-->
<option value="0">
請選擇
</option>
</select>
</td>
</tr>
<tr>
<td>
</td>
<tr>
</table>
</form>
</div>
</body>
</html>
SelectServlet:
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);
// 獲得請求中參數為id的值
String xml_start = "<selects>";
String xml_end = "</selects>";
String xml = "";
if (targetId.equalsIgnoreCase("0"))
{
xml = "<select><value>0</value><text>請選擇</text></select>";
} else if (targetId.equalsIgnoreCase("1"))
{
xml = "<select><value>1</value><text>昌平</text></select>";
xml += "<select><value>2</value><text>豐臺</text></select>";
xml += "<select><value>3</value><text>海淀</text></select>";
xml += "<select><value>4</value><text>朝陽</text></select>";
} else if (targetId.equalsIgnoreCase("2"))
{
xml = "<select><value>1</value><text>塘沽區</text></select>";
xml += "<select><value>2</value><text>漢沽區</text></select>";
xml += "<select><value>3</value><text>大港區</text></select>";
xml += "<select><value>4</value><text>東麗區</text></select>";
} else
{// 如果是3,則返回下面的字符
xml = "<select><value>1</value><text>濟南</text></select>";
xml += "<select><value>2</value><text>青島</text></select>";
xml += "<select><value>3</value><text>淄博</text></select>";
xml += "<select><value>4</value><text>棗莊</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>
看完上述內容，你們掌握Ajax中二級聯動菜單的實現原理是什么的方法了嗎？如果還想學到更多技能或想了解更多相關內容，歡迎關注億速云行業資訊頻道，感謝各位的閱讀！
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