Ajax入门

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<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<TITLE>Ajax验证用户名是否存在例子</TITLE>
<script>

//设一个变量

var XMLHttpReq=false;
   //创建一个XMLHttpRequest对象
   function createXMLHttpRequest(){
     if(window.XMLHttpRequest){ //Mozilla
      XMLHttpReq=new XMLHttpRequest();
      }
      else if(window.ActiveXObject){
       try{
        XMLHttpReq=new ActiveXObject("Msxml2.XMLHTTP");
        }catch(e){
         try{
          XMLHttpReq=new ActiveXObject("Microsoft.XMLHTTP");
          }catch(e){}
          }
         }
        }
   //发送请求函数
   function send(url){
    createXMLHttpRequest();
    XMLHttpReq.open("get",url,true);
    XMLHttpReq.onreadystatechange=proce;   //指定响应的函数
    XMLHttpReq.send(null); //发送请求
    }
   function proce(){
    if(XMLHttpReq.readyState==4){ //对象状态
     if(XMLHttpReq.status==200){//信息已成功返回，开始处理信息
                 
     var root=XMLHttpReq.responseXML;
     var res=root.getElementsByTagName("content")[0].firstChild.data;
     window.alert(res);
      
     //var xmlReturn = XMLHttpReq.responseText;
     //window.alert(xmlReturn);
     }else{
      window.alert("所请求的页面有异常");
      }
      }
      }
   //身份验证
   function check(){
    var name=document.getElementById("name").value;

     if(name==""){
      alert("请输入姓名!");
      return false;
      }
      else{
       //send('login?name='+name);
       document.getElementById("load").style.display='';
       send('login.do?name='+name);
       document.getElementById("load").style.display='none';
       }
      }

   </script>
</head>

<body>
<form action="login" method="post">
   <table>
       <tr><td>姓名: <input id="name" type="text" name="name"/><p>
        <div id=load style="display:none; position:absolute;right:0px;top:0px;background:#FF5B5B;border:1px solid">正在验证用户名,请稍后……</div><p>
          <input type="button" value="检测!" onClick="check()"/>
       </td>
      </tr>
      </table>
      </form>
</body>
</html>

structs-config配置:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.2//EN" "http://struts.apache.org/dtds/struts-config_1_2.dtd">

<struts-config>
<data-sources />
<form-beans >
<form-bean name="loginForm" type="org.viman.struts.form.LoginForm" />

</form-beans>

<global-exceptions />
<global-forwards />
<action-mappings >
    <action
      attribute="loginForm"
      input="/login.jsp"
      name="loginForm"
      path="/login"
      scope="request"
      type="org.viman.struts.action.LoginAction" />

</action-mappings>

<message-resources parameter="org.viman.struts.ApplicationResources" />
</struts-config>

action实现(LoginAction.java):

package org.viman.struts.action;

import java.io.UnsupportedEncodingException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.viman.struts.form.LoginForm;

/**
* MyEclipse Struts
* Creation date: 01-06-2007
*
* XDoclet definition:
* @struts.action path="/login" name="loginForm" input="/login.jsp" scope="request" validate="true"
*/
public class LoginAction extends Action {
/*
* Generated Methods
*/

/**
* Method execute
* @param mapping
* @param form
* @param request
* @param response
* @return ActionForward
*/
public ActionForward execute(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response) {
  //LoginForm loginForm = (LoginForm) form;// TODO Auto-generated method stub
  try {
      request.setCharacterEncoding("gb2312");
     } catch (UnsupportedEncodingException e) {
      e.printStackTrace();
     }
     try{
      String msgStr="";
      response.setContentType("text/xml;charset=GB2312");
      response.setHeader("Cache-Control","no-cache");
      String name=(String)request.getParameter("name");
      System.out.println("name = "+name);
      if("gong".equals(name)){ //找查数据库中有无该用户名
      msgStr ="对不起,此用户名已经存在,请更换用户名注册!";
      }else{
      msgStr ="用户未被注册,可以使用!";
      }
      response.getWriter().println("<?xml version='1.0' encoding='GB2312' ?>");
      response.getWriter().println("<root>");
      response.getWriter().println("<content>");
      response.getWriter().print(msgStr);
      response.getWriter().println("</content>");
      response.getWriter().println("</root>");
      response.getWriter().close();
      }catch(Exception ex){

}
return null;

}