Symfony 3 API. Returning form errors as json

ExceptionListener.php

<?php

namespace AppBundle\Event\Listener;


use AppBundle\Exception\ValidationException;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;

class ExceptionListener
{
    public function onKernelException(GetResponseForExceptionEvent $event) {

        $exception = $event->getException();

        if (!$exception instanceof ValidationException) {
            return;
        }

        $response = new JsonResponse(
            [
                'code' => $exception->getStatusCode(),
                'message' => $exception->getMessage(),
                'errors'=> $this->convertFormToArray($exception->getForm())
            ]
        );

        $event->setResponse($response);
    }

    /**
     * This code has been taken from JMSSerializer.
     */
    private function convertFormToArray(FormInterface $data)
    {
        $form = $errors = [];

        foreach ($data->getErrors() as $error) {
            $errors[] = $error->getMessage();
        }

        if ($errors) {
            $form['errors'] = $errors;
        }

        $children = [];
        foreach ($data->all() as $child) {
            if ($child instanceof FormInterface) {
                $children[$child->getName()] = $this->convertFormToArray($child);
            }
        }

        if ($children) {
            $form['children'] = $children;
        }

        return $form;
    }
}

IndexController.php

<?php namespace AppBundle\Controller;

use AppBundle\Exception\ValidationException;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class InboxController extends Controller
{
  public function createAction(Request $request) {
    ...
      
    if ($form->getErrors()) {
      throw new ValidationException($form);
    }
    
    ...
  }
}

ValidationException.php

<?php

namespace AppBundle\Exception;


use Symfony\Component\Form\FormInterface;
use Symfony\Component\HttpKernel\Exception\HttpException;

class ValidationException extends HttpException
{
    /**
     * @var FormInterface
     */
    private $form;

    /**
     * ValidationException constructor.
     * @param FormInterface $form
     */
    public function __construct(FormInterface $form)
    {
        $this->form = $form;

        parent::__construct(400, 'Validation Failed');
    }

    /**
     * @return FormInterface
     */
    public function getForm()
    {
        return $this->form;
    }
}