ajax验证用户名是否存在

<script type="text/javascript">
<!--
 var __ajaxRequest=false;
 var __inited=false;
 var __container=false;
 function __init(){
  __inited=true;
  if(window.ActiveXObject){
   try{
    __ajaxRequest=new ActiveXObject("Msxml2.XMLHTTP");
   }catch(e){
    try{
     __ajaxRequest=new ActiveXObject("Microsoft.XMLHTTP");
    }catch(ee){
    }
   }
  }
  if(!__ajaxRequest){
   alert("can't init");
  }else{
   __ajaxRequest.onreadystatechange=function(){
    if(__ajaxRequest.readyState==4){
     if(__ajaxRequest.status==200){
      confirmDiv.innerText=__ajaxRequest.responseText;
     }
    }
   };
   __ajaxRequest.open("POST","/JBlog/common/registe.do?action=checkUserName",true);
   __ajaxRequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
  }
 }
 
 function __sendData(){
  if( userRegForm.userName.value == ""){
   confirmDiv.innerText = "请先填写用户名";
   return ;
  }
  __init();
  var data = "userName="+ userRegForm.userName.value;
  __ajaxRequest.send(data);
 }
//-->
</script>

 

<tr>
     <td width="20%" align="right">用户名:</td>
     <td align="center"><html:text property="userName" />
     <td style="color: #ff0000;width: 40%;">*</td>
    </tr> 
    <tr>
     <td align="right"></td>
     <td align="center"><a href="javascript:__sendData()">检查用户名是否可用</a></td>
     <td><div id="confirmDiv"></div></td>
    </tr>

 

.java文件

String name = request.getParameter("userName");
  
  String result = "";
  
  if( checkUserExists(name) ) {
   result = getResources(request, "abc").getMessage("已存在此用户名");
  } else {
   result = getResources(request, "abc").getMessage("此用户名未被使用");
  }
  
  try {
   response.setContentType("text/html; charset=gb2312");
   response.getWriter().println(result);
  }catch(Exception e) {
   e.printStackTrace();
  }

public checkUserExists(String name){
      验证
}