Ajax+Struts做登录判断

/*
* 登录
*/
public ActionForward doLogin(ActionMapping  mapping,ActionForm form,HttpServletRequest request,HttpServletResponse response) throws IOException
{

//获得表单数据
int uid=Integer.parseInt(request.getParameter("petID"));
String pwd=request.getParameter("pwd");
PrintWriter out=response.getWriter();
//根据ID获得其信息
PetInfo info=petInfoBiz.getPetInfoByID(uid);
if(info==null)
{
out.print(0);
return null;
}
else if(!petInfoBiz.login(uid, pwd))
{
out.print(1);
return null;
}
else if(petInfoBiz.login(uid, pwd))
{
out.print(2);
return null;
}

return null;
}

//根据IE的类型创建一个XmlHttpRequest对象
function createXmlHttpRequest()
{
if(window.ActiveXObject)
{
return new ActiveXObject("Microsoft.XMLHTTP");
}
else if(window.XMLHttpRequest)
{
return new XMLHttpRequest;
}
}

var xmlHttpRequest;
//根据宠物编号发送请求到服务器
function requestServer()
{
var loginState=document.getElementById("loginState");
with(document.petForm)
{

if(petID.value=="")
{
loginState.innerText="请填写宠物编号！";
}
else if(isNaN(petID.value))
{
loginState.innerText="编号不合法";
}
else if(pwd.value=="")
{
loginState.innerText="请填写密码";
}
else
{
var url="doPetInfo.do?methodName=doLogin&petID="+petID.value+"&pwd="+pwd.value;
//创建XMLHttpRequest组件
xmlHttpRequest=createXmlHttpRequest();
//设置回调函数，让其等待服务器的响应
xmlHttpRequest.onreadystatechange=doLogin;
//初始化xmlHttpRequest组件,传入URL
xmlHttpRequest.open("GET",url,true);
//发送请求
xmlHttpRequest.send(null);
}
}
}
//登录，获得服务器返回的信息并做出相应提示
function doLogin()
{
var loginState=document.getElementById("loginState");
if(xmlHttpRequest.readyState==0)
{
loginState.innerText="未初始化...";
}
if(xmlHttpRequest.readyState==1)
{
loginState.innerText="初始化中...";
}
if(xmlHttpRequest.readyState==2)
{
loginState.innerText="正在向服务器发送请求...";
}
if(xmlHttpRequest.readyState==3)
{
loginState.innerText="正在验证登录信息...";
}
if(xmlHttpRequest.readyState==4)
{
loginState.innerText="验证完成...";
}
if(xmlHttpRequest.readyState==4 && xmlHttpRequest.status==200)
{
var text=xmlHttpRequest.responseText;
if(text=="0")
{
loginState.innerText="此ID不存在";
}
else if(text=="1")
{
loginState.innerText="密码错误";
}
else if(text=="2")
{
loginState.innerText="验证成功...";
location.href="doPetInfo.do?methodName=doInit&petID="+document.petForm.petID.value;
}
}
}

<span id="loginState" style="color:red"></span>     
宠物ID：<input type="text" name="petID" size="6" value="">
密码：<input type="password" name="pwd" size="6" value="">    
<button onclick="requestServer()">登录</button>