[Symfony] Creating an event subscriber for a 404 NotFoundHttpException

Published on 2023-03-30 • Modified on 2023-03-30

This snippet shows how to create an event subscriber for a 404 NotFoundHttpException. Here, we test if a given path was accessed (this path doesn't math any application route). We can also log something or notify; check out the documentation example. You can test the snippet here.

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<?php

declare(strict_types=1);

namespace App\Subscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Event\ExceptionEvent;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

final class NotFoundExceptionSubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array
    {
        return [
            ExceptionEvent::class => 'onKernelException',
        ];
    }

    public function onKernelException(ExceptionEvent $event): void
    {
        $exception = $event->getThrowable();
        if ($exception instanceof NotFoundHttpException) {
            $path = $event->getRequest()->getPathInfo();
            if ($path === '/404') {
                $event->setResponse(new Response('404 found!'));
                $event->stopPropagation();
            }
        }
    }
}

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