jQuery验证注册信息和 用户名是否存在

 <script type='text/javascript' src='${pageContext.request.contextPath }/web/js/jquery.js'></script>
  <script type='text/javascript' src='${pageContext.request.contextPath }/web/js/jquery.validate.js'></script>
var flag = false;
      function registsubmit(){
          var s = $('#ccusername').val();
          var url = "loginNameUser.action?userName="+s+"&seed="+Math.random();
          if(checkEmpty()) {
            return false;
        } else {
            if(flag == true){
                  //如果用户名不存在，可以提交
                $("#formregist").validate({
                    onsubmit:true,
                    rules:{
                        "user.ccusername":{
                            required:true
                        },
                        "user.ccpassword":{
                            required:true
                        },
                        "pswd2":{
                            equalTo:"#pswd1"
                        },
                        "user.ccquestion":{
                            required:true
                        },
                        "user.ccemail":{
                            required:true,
                            email:true
                        }
                    },
                    messages:{
                        "user.ccusername":{
                            required:"用户名不能为空！"
                        },
                        "user.ccpassword":{
                            required:"请填写密码！"
                        },
                        "pswd2":{
                            equalTo:"两次密码不一致"
                        },
                        "user.ccquestion":{
                            required:"问题答案不能为空！"
                        },
                        "user.ccemail":{
                            required:"邮箱不能为空！",
                            email:"不符合邮箱格式！"
                        }
                    }
                 });
              } else{
                  $("#existUserName").empty();
                $("#existUserName").append("<font color='red'>该用户已存在！</font>");
                  return false;
              }
        }
      }
      $(function() {
          $("#ccusername").change(function() {
            if(checkEmpty()) {
                return false;
            } else {
                var userName = $('#ccusername').val();
                  var url = "loginNameUser.action?userName="+userName+"&seed="+Math.random();
                  $.post(url , {
                          userName : $('#ccusername').val()
                      },function(data , textStatus) {
                          if(data == "true") {
                              $("#existUserName").empty();
                              $("#existUserName").append("<font color='red'>该您可以注册</font>");
                              flag = true;
                          } else {
                              $("#existUserName").empty();
                              $("#existUserName").append("<font color='red'>该用户已存在！</font>");
                          }
                      }        
                  );
              }
          });
      });
      function checkEmpty() {
          var userName = $('#ccusername').val();
        if(userName == null || $.trim(userName) == '') {
            $("#existUserName").empty();
            $("#existUserName").append("<font color='red'>用户名不能为空</font>");
            return true;
        } else {
            return false;
        }
      }