404 NotFoundHttpException hatası oluştuğunda, kullanıcıyı onKernelException event listener ile başka bir sayfaya yönlendirme

services:
    application_backend.event_listener.kernel_exception:
        class: Application\BackendBundle\EventListener\KernelExceptionListener
        arguments: [@router]
        tags:
            - { name: kernel.event_listener, event: kernel.exception, method: onKernelException }

namespace Application\BackendBundle\EventListener;

use Symfony\Bundle\FrameworkBundle\Routing\Router;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

class KernelExceptionListener
{
    private $router;
    private $redirectRouter = 'application_frontend_default_index';

    public function __construct(Router $router)
    {
        $this->router = $router;
    }

    public function onKernelException(GetResponseForExceptionEvent $event)
    {
        $exception = $event->getException();

        if ($exception instanceof NotFoundHttpException) {
            if ($event->getRequest()->get('_route') == $this->redirectRouter) {
                return;
            }

            $url = $this->router->generate($this->redirectRouter);
            $response = new RedirectResponse($url);
            $event->setResponse($response);
        }
    }
}