Hi i have check your response get one issue
String response = "{success\":\"true\",\"user_id\": \"1\",\"userFirstName\":\"username\", \"userRank\": \"99\"}";
its in json validation display valid but in success key not " in starting so its create json object like
{"userFirstName":"username","user_id":"1","success\"":"true","userRank":"99"}
so its could not get values from success
Write things like
String response = "{\"success\":\"true\",\"user_id\": \"1\",\"userFirstName\":\"username\", \"userRank\": \"99\"}";
and it should parse like this
try {
JSONObject jobj = new JSONObject(response);
String succes = jobj.getString("success");
String userFirstName = jobj.getString("userFirstName");
String user_id = jobj.getString("user_id");
String userRank = jobj.getString("userRank");
String user_id = jobj.getString("user_id");
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}