private void addOne(RoutingContext routingContext) {
   FactorizationTask task =
       Json.decodeValue(routingContext.getBodyAsString(), FactorizationTask.class);
   task = service.create(task.getNumber());
   routingContext
       .response()
       .setStatusCode(201)
       .putHeader("content-type", "application/json; charset=utf-8")
       .end(Json.encodePrettily(task));
 }