AJAX里req.responseXML.documentElement返回null的问题 - Web 开发 / Ajax
在做一个老项目，没办法用DWR,重新拿起了ajax。
在网上找的代码，结果后台servlet里面是可以调用到的，并且有值。但是到前台返回的时候，req.responseXML.documentElement是空的。
已经尝试过调整编码格式，writer.close()方法和writer.flush()方法了。但是确实取不到返回值。
代码如下
index.jsp
<%@ page language="java" contentType="text/html; charset=utf-8"%>
<html>
<head>
<title>My JSP 'index.jsp' starting page</title>
<http-equiv="Content-Type" content="text/html; charset=utf-8">
<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 zhi = document.getElementById("hero").options[document.getElementById("hero").selectedIndex].value;
alert(zhi);
var url = "select?id="+escape(zhi);
if(window.XMLHttpRequest){
req = new XMLHttpRequest();
}else if(window.ActiveXObject){
req = new ActiveXObject("Microsoft.XMLHTTP");
}
if(req){
req.open("GET",url,true);
req.onreadystatechange = callback; //指定回调函数为callback
req.send(null);
}
}
function callback(){
if(req.readyState ==4){
if(req.status ==200){
parseMessage();//解析XML文档
}else{
alert(req.status);
alert("Not able to retrieve description" + req.statusText);
}
}
}
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('skill');
//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%" boder="0" cellspacing="0">
<TR>
<TD align="center">Double Select Box</TD>
</TR>
<TR>
<TD>
<SELECT name="hero" id="hero" onChange="Change_Select()">
<OPTION ="0" value="0">Unbounded</OPTION>
<OPTION ="1" value="1">D.K.</OPTION>
<OPTION ="2" value="2">NEC.</OPTION>
<OPTION ="3" value="3">BOSS</OPTION>
</SELECT>
<SELECT name="skill" id="skill">
<OPTION ="0">Unbounded</OPTION>
</SELECT>
</TD>
</TR>
<TR><td> </td></TR>
</TABLE>
</form>
</div>
</body>
</html>
SelectServlet.java
package com;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class SelectServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public SelectServlet() {
super();
}
/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/xml;utf-8");
response.setHeader("Cache-Control","no-cache");
String targetId=request.getParameter("id").toString();
String xml_start="<selects>";
String xml_end="</selects>";
String xml="";
System.out.println("------------------targetId------>>>"+targetId);
if(targetId.equalsIgnoreCase("0")){
xml="<select><>0</><text>Unbounded</text></select>";
}else if(targetId.equalsIgnoreCase("1")){
System.out.println("------------------->>>"+targetId);
xml="<select><>1</><text>Mana Burn</text></select>";
xml +="<select><>2</><text>Death Coil</text></select>";
xml +="<select><>3</><text>Unholy Aura</text></select>";
xml +="<select><>4</><text>Unholy Fire</text></select>";
}else if(targetId.equalsIgnoreCase("2")){
xml="<select><>1</><text>Corprxplode</text></select>";
xml +="<select><>2</><text>Raise Dead</text></select>";
xml +="<select><>3</><text>Brilliance Aura</text></select>";
xml +="<select><>4</><text>Aim Aura</text></select>";
}else{
xml="<select><>1</><text>Rain of Chaos</text></select>";
xml +="<select><>2</><text>Finger of Death</text></select>";
xml +="<select><>3</><text>Bash</text></select>";
xml +="<select><>4</><text>Summon Doom</text></select>";
}
String last_xml=xml_start+xml+xml_end;
System.out.println("--------------------><"+last_xml);
PrintWriter writer = response.getWriter();
writer.write(last_xml);
writer.flush();
writer.close();
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
/**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occure
*/
public void init() throws ServletException {
// Put your code here
}
}
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>
哪位大大帮我看看啊
[解决办法]
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'LianDongJsp.jsp' starting page </title>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<script type="text/javascript">
var req;
window.onload = function(){
}
function Change_Select(){
var zhi=document.getElementById("hero").value;
var url="select?id="+escape(zhi);
if(window.XMLHttpRequest){
req = new XMLHttpRequest();
}else if(window.ActiveXObject){
req = new ActiveXObject("Microsoft.XMLHTTP");
}
if(req){
req.open("GET",url,true);
req.onreadystatechange = callback;
req.send(null);
}
}
function callback(){
if(req.readyState == 4){
if(req.status == 200){
parseMessage();
}else{
alert("Not able to retrieve description" + req.statusText);
}
}
}
function parseMessage(){
var xmlDoc = req.responseXML.documentElement;
var xSel = xmlDoc.getElementsByTagName('select');
var select_root = document.getElementById('skill');
select_root.options.length = 0;
for(var i=0; i <xSel.length;i++){
var xValue = xSel[i].childNodes[1].firstChild.nodeValue;
var xText = xSel[i].childNodes[3].firstChild.nodeValue;
var option = new Option(xText,xValue);
try{
select_root.options.add(option);
}catch(e){
}
}
}
</script>
</head>
<body>
<div align="center">
<form name="form1" method="post" action="">
<table width="70%" boder="0" cellspacing="0">
<tr>
<td align="center">
Double Select Box
</td>
</tr>
<tr>
<td>
<select name="hero" id="hero" onchange="Change_Select()">
<option value="0">
Unbounded
</option>
<option value="1" selected="selected">
D.K
</option>
<option value="2">
NEC.
</option>
<option value="3">
BOSS
</option>
</select>
<select name="skill" id="skill">
<option value="0">
Unbounded
</option>
</select>
</td>
</tr>
<tr>
<td>
</td>
</tr>
</table>
</form>
</div>
</body>
</html>
