I mean creating an error 400, 500 generated by the ViewHandler of Fosrestbundle directly from the controller without using an Entity and a Form.
I don't know if i understood you question correctly but there are some possibilities.
return $this->view(null, 400);
You can return the view with the status code. In some cases i thow an HTTPException
.
use Symfony\Component\HttpKernel\Exception\HttpException;
throw new HttpException(400, "Input not correct or not allowed!");
There you can define the status code and the error message.