How to dynamically load combo boxes with Ajax (code attached)
This time I will show you how to dynamically load a combo box with Ajax (with code). What are the precautions for Ajax to dynamically load a combo box? The following is a practical case, let's take a look.
一 province.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<html>
<head>
<script type="text/javascript" language="javaScript">
var xmlHttp = false; //全局变量，用于记录XMLHttpRequest对象
function createXMLHttpRequest() {
if(window.ActiveXObject) { //Internet Explorer时，创建XMLHttpRequest对象的方法
try {
xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch(e) {
try { xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
//旧版本的Internet Explorer，创建XMLHttpRequest对象
} catch(e) {
window.alert("创建XMLHttpRequest对象错误"+e);
}
}
} else if(window.XMLHttpRequest) { //mozilla时，创建XMLHttpRequest对象的方法
xmlHttp = new XMLHttpRequest();
}
if(!(xmlHttp)) { //未成功创建XMLHttpRequest对象
window.alert("创建XMLHttpRequest对象异常！");
}
}
//下拉列表项改变时的操作
function proChange(objVal) {
createXMLHttpRequest(); //创建XMLHttpRequest对象
document.getElementById("city").length = 1; //根据ID获取指定元素，并赋值
xmlHttp.onreadystatechange = cityList; //指定onreadystatechange处理函数
var url="CityByXMLServlet?province="+objVal; //请求的URL地址
xmlHttp.open("POST",url,true);
xmlHttp.send(null);
}
function cityList() { //onreadystatechange的处理函数
if(xmlHttp.readyState==4) {
if(xmlHttp.status==200) {
parseXML(xmlHttp.responseXML); //解析服务器返回的XML数据
}
}
}
//解析xml信息，以添加地市
function parseXML(xmlDoc) {
var len = xmlDoc.getElementsByTagName("city");
//获取XML数据中所有的“city”元素对象集合
var _citySel = document.getElementById("city"); //根据ID获取页面中的select元素
for(var i=0;i<len.length;i++) { //遍历XML数据并给select元素添加选项
var opt = document.createElement("OPTION"); //创建option对象
opt.text = xmlDoc.getElementsByTagName("city")[i].firstChild.data;
//指定新创建元素的text属性值
opt.value = xmlDoc.getElementsByTagName("city")[i].firstChild.data;
//指定新创建元素的value属性值
_citySel.add(opt); //为select元素添加option
}
}
</script>
<title>动态加载组合框</title>
</head>
<body>
<table align="center" border=1 width="320">
<tr>
<td>省份：</td>
<td>
<select id="province" onChange="proChange(this.value);" style="width:85">
<option value="gd">广东</option>
<option value="gx">广西</option>
<option value="hn">湖南</option>
<option value="hb">湖北</option>
<option value="ah">安徽</option>
</select>
</td>
</tr>
<tr>
<td>城市：</td>
<td>
<select id="city" style="width:85">
<option value="">--请选择--</option>
</select>
</td>
</tr>
</table>
</body>
</html>二、CityByXMLServlet.java
package servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.*;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class CityByXMLServlet
*/
@WebServlet("/CityByXMLServlet")
public class CityByXMLServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final String CONTENT_TYPE = "text/xml; charset=UTF-8";
/**
* @see HttpServlet#HttpServlet()
*/
public CityByXMLServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType(CONTENT_TYPE); //设置服务器响应类型
String province =request.getParameter("province");
StringBuffer city = new StringBuffer("<citys>"); //记录返回XML串的对象
if("gx".equals(province)){
List list=cityInit(); //获取城市列表
for(int i=0;i<list.size();i++){
city.append("<city>"+list.get(i)+"</city>");
}
}else if("hn".equals(province)){
List list = cityInit1(); //获取城市列表
for(int j=0;j<list.size();j++){
city.append("<city>"+list.get(j)+"</city>");
}
}else if("hb".equals(province)){
List list = cityInit2(); //获取城市列表
for(int j=0;j<list.size();j++){
city.append("<city>"+list.get(j)+"</city>");
}
}
city.append("</citys>");
PrintWriter out = response.getWriter();
out.println(city.toString());
out.flush(); //输出流刷新
out.close(); //关闭输出流
}
/*
* 初始化城市
*/
public List<String> cityInit2() {
List<String> cityList = new ArrayList<String>();
//添加城市列表
cityList.add("武汉");
cityList.add("襄阳");
cityList.add("黄冈");
cityList.add("荆门");
cityList.add("十堰");
cityList.add("黄石");
return cityList;
}
public List<String> cityInit(){
List<String> cityList = new ArrayList<String>();
//添加城市列表
cityList.add("南宁");
cityList.add("桂林");
cityList.add("北海");
cityList.add("河池");
cityList.add("梧州");
cityList.add("玉林");
return cityList;
}
public List<String> cityInit1() {
List<String> cityList = new ArrayList<String>();
//添加城市列表
cityList.add("长沙");
cityList.add("湘潭");
cityList.add("岳阳");
cityList.add("常德");
cityList.add("衡阳");
cityList.add("邵阳");
return cityList;
}
/**
*当前Servelt的初始化方法. <br>
*
* @throws ServletException发生ServletExceptio时抛出
*/
public void init() throws ServletException {
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}三web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:web="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd http://xmlns.jcp.org/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.4"> <servlet> <servlet-name>CityByXMLServlet</servlet-name> <servlet-class>servlet.CityByXMLServlet</servlet-class><!--类的位置 --> </servlet> <servlet-mapping> <servlet-name>CityByXMLServlet</servlet-name><!--你创建的类名 --> <url-pattern>/CityByXMLServlet</url-pattern> </servlet-mapping>
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