AJAX 前后端交互 验证信息是否正确

1、前段：

 1 function checkPtCode(obj){
 2     $.ajax({
 3         type: "post",
 4         url: "xxxxxxx",
 5         data: {"xx":obj.value},
 6         cache: false,
 7         async : true,
 8         dataType:"json",
 9         type:"POST",
10         success: function (result){
11         if(result.flag == "No"){
12             jAlert("编码库不存在此编码，请修正！");
13         }
14          }
15      });
16 }       

2、后端

 1 public void checkPtCode(HttpServletRequest request,
 2             HttpServletResponse response) throws IOException {
 3         PrintWriter out = response.getWriter();
 4         JSONObject json = new JSONObject();
 5         try {
 6             response.setContentType("text/html;charset=UTF-8");
 7             response.setContentType("text/html");
 8             response.setHeader("Cache-Control", "no-store");
 9             response.setHeader("Pragma", "no-cache");
10             response.setDateHeader("Expires", 0);
11             String ptCode = request.getParameter("ptCode");
12             
13             if(ptCode != null && ptCode.trim().length() != 0){
14                 // 编码库校验
15                 List<DrpProductType> list = this.controlRelationService.checkCode(ptCode);
16                 if(list != null && list.size() != 0){
17                     json.put("flag", "ok");
18                     out.print(json.toString());
19                 }else {
20                     json.put("flag", "No");
21                     out.write(json.toString());
22                 }
23             }
24         } finally {
25             out.close();
26         }
27     }