List<Guest> list = guestService.getAllGuests();
JSONArray array = new JSONArray();
for (Guest guest : list) {
JSONObject guestJson = new JSONObject();
guestJson.accumulate("id", guest.getId())
.accumulate("username", guest.username)
.accumulate("firstname", guest.firstname)
.accumulate("lastname", guest.lastname)
.accumulate("email", guest.email)
.accumulate("roles", guest.getUserRoles());