Ajax java struts 實現使用者名稱驗證

//使用者名稱驗證的struts

package com.mobi5.web.struts.action;

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

import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;

import com.mobi5.commons.domain.Sys_MobileUser_Reginfo;

public class ValidUsernameAction extends BaseAction {
 public ActionForward execute(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response)
   throws Exception {
  String username = request.getParameter("user_name");
  username = new String(username.trim().getBytes("ISO8859_1"), "gbk");
  Sys_MobileUser_Reginfo user = new Sys_MobileUser_Reginfo();
  user.setUser_name(username);
  //user = this.getIdService().getUserByUsername(username);
  user=this.getIdService().getUserInfoBy(user);
  String message = "";
  if (user != null) {
   message = "1";
   response.setContentType("text/xml; charset=gbk");
   response.getWriter().write(message);
   response.getWriter().close();
  } else {
   message = "0";
   response.setContentType("text/xml; charset=gbk");
   response.getWriter().write(message);
   response.getWriter().close();
  }
  return null;
 }
}

//jsp 頁面

 

//驗證使用者名稱是否存在
 var xmlHttp;
 function createXMLHttpRequest(){
  if(window.XMLHttpRequest)
  {
   xmlHttp = new XMLHttpRequest();
  }else if(window.ActiveXObject)
  {
   xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
  }
 
 }
 
 function valid(){
    
  if(form2.user_name.value=="" || trim(form2.user_name.value).length ==0){
   alert("使用者名稱不可為空！")
   return false;
  }
  var message = document.getElementById("message1");
  
  message.innerHTML="";
  createXMLHttpRequest();
  
  window.status ='';
  url ="validUsernameAction.do?user_name="+document.form2.user_name.value;
  xmlHttp.open("GET",url,true);
  xmlHttp.onreadystatechange = validUsername;
  xmlHttp.send(null);
 
 }
 
 function validUsername(){
  
  if (xmlHttp.readyState == 4)
  {
   if (xmlHttp.status == 200 || xmlHttp.status == 0)
   {
    resText = xmlHttp.responseText;
    if(resText=="1"){
     var message = document.getElementById("message1");
     message.innerHTML="<span style='color:red'>&nbsp;&nbsp;<b>使用者名稱已經存在，請選用其它使用者名稱！</b></span>";
     form2.user_name.value="";
     form2.user_name.focus();
    }else {
     var message = document.getElementById("message1");
     message.innerHTML="<span style='color:red'>&nbsp;&nbsp;<b>使用者名稱可以使用！</b></span>";
    }
   }
  }
 }