@Override
 @POST
 @Path("/deviceid/")
 public String usernameFromDeviceId(@FormParam("deviceid") final String id) {
   Device device = findDeviceByDeviceId(id);
   if (device == null) {
     return "{\"deviceExists\":false}";
   }
   if (device.getUsername() == null || device.getUsername().length() == 0) {
     return "{\"deviceExists\":true,\"hasUsername\":false}";
   } else {
     return "{\"deviceExists\":true,\"hasUsername\":true,\"username\":\""
         + device.getUsername()
         + "\"}";
   }
 }