Obtaining JSON data from server into $.ajax call - json

Question

I have a problem with JSON and JQUERY. In my web application I submit some data (through an $.ajax call) to a servlet and want to receive back some informations from this servlet once it has done.
I'm using JSONObject in this way:
function check(){
$.ajax({
url: "/check",
type: "POST",
dataType: "json",
success: on_check_ok,
error: function(){
alert("something wrong happened");
},
data: {
players_code: $("#players_code").val(),
},
});
return false;
}
function on_check_ok(data) {
var json = data;
$("#display").text(json.check); //"display" is a <div> into index.html
};
and this is doPost() method in my servlet code:
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
response.setContentType("application/json");
PrintWriter out = response.getWriter();
String code_array = request.getParameter("players_code");
System.out.println("Player's code is: " + code_array);
int arr = Integer.parseInt(code_array);
LinkedList<Integer> stack = new LinkedList<Integer>();
while(arr > 0){
stack.push(arr%10);
arr = arr/10;
}
int index = 0;
while(!stack.isEmpty()){
array[index] = (int)stack.pop();
index++;
}
mm.checkGuess(array);
response.getWriter().write(mm.ris + " ");
tries++;
System.out.println("TRIES: " + tries);
JSONObject obj = new JSONObject();
obj.put("check", tries);
String json = obj.toString();
out.write(json);
System.out.println("JSON " + json);
}
}
but cannot get displayed any information. Seems that JSONObject has been created correctly, since I can display it on console. I'm having hard times on getting this data back to javascripts.
That's my code, what I'm doing wrong? Or, is there an alternative way to get the same result? thanks for the help!