jQuery用户名验证

<script type="text/javascript"
src="${pageContext.request.contextPath}/js/xmlHttpRequest.js"></script>
<script type='text/javascript'
src='${pageContext.request.contextPath}/js/index.js'></script>
<script type="text/javascript"
src="${pageContext.request.contextPath}/js/jquery-1.6.1.js"></script>
<script type="text/javascript">
   $(function(){
    var username = $("#username");
    var msg = $("#msg");
    var submit =$("#submit");
    username.blur(function(){
        alert(username.val())
        if(username.val()==""){
            msg.html("<font color='red'>请填写用户名！</font>");
            return;
        }                           
        var date = new Date();
        $.ajax({
            type:"get",
            url:"${pageContext.request.contextPath}/UserController",
            data:{  flag : "checkUser" ,
                    username : username.val()},     
            dataType:"text",
            success:function(data){                 
                if (data.length>5){
                    msg.html("<font color='red'>"+data+"</font>");
                    submit.attr("disabled",true);
                }else{
                    msg.html("<font color='green'>"+data+"</font>");
                    submit.attr("disabled",false);
                }
            }
            
        });
    }); 
 });

servlet代码：

 /*
 * 校验用户名是否存在
 */
private void checkUser(HttpServletRequest request,HttpServletResponse response) throws IOException {
    String username = "";
    if (request.getParameter("username") != null
            && !"".equals(request.getParameter("username"))) {
        username = request.getParameter("username");
    }
    System.out.println("username:"+username);
    PrintWriter out = response.getWriter();
    UserService userService = new UserService();
    int checkUser = userService.checkUser(username);
    System.out.println(checkUser);
    if(checkUser == 1){
        out.print("用户名已存在");
    }else if(checkUser == 0){
        out.print("用户名可用");
    }
}