composer require template

catch:
    path: /{any}
    controller: App\Controller\DefaultController::catch
    requirements:
        any: ".*"

<?php

namespace App\Controller;

use Symfony\Component\HttpFoundation\Response;

class DefaultController
{
    public function catch()
    {
        return new Response('Page not found.', 404);
    }
}

services:
    App\EventListener\ExceptionListener:
        tags:
            - { name: kernel.event_listener, event: kernel.exception }
        arguments:
            $kernelEnvironment: "%kernel.environment%"

<?php

namespace App\EventListener;

use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

class ExceptionListener
{
    private $kernelEnvironment;

    public function __construct(string $kernelEnvironment)
    {
        $this->kernelEnvironment = $kernelEnvironment;
    }

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

        if ($exception instanceof NotFoundHttpException && $this->kernelEnvironment == 'prod') {
            $message = "Page not found.";
            $response = new Response();
            $response->setContent($message);
            $response->setStatusCode($exception->getStatusCode());
            $response->headers->replace($exception->getHeaders());
            $event->setResponse($response);
        }
    }
}

HTTP/1.1 200 OK
Date: Sun, 11 Feb 2018 08:45:09 GMT
Server: Apache/2.4.25 (Debian)
X-Powered-By: PHP/7.2.2
Vary: Accept-Encoding
Content-Length: 1174
Content-Type: text/html; charset=UTF-8

<br />
<b>Fatal error</b>:  Uncaught Symfony\Component\Routing\Exception\ResourceNotFoundException in /var/www/html/var/cache/prod/srcProdProjectContainerUrlMatcher.php:37
Stack trace:
#0 /var/www/html/vendor/symfony/routing/Matcher/UrlMatcher.php(95): srcProdProjectContainerUrlMatcher-&gt;match('/foo')
#1 /var/www/html/vendor/symfony/routing/Router.php(262): Symfony\Component\Routing\Matcher\UrlMatcher-&gt;matchRequest(Object(Symfony\Component\HttpFoundation\Request))
#2 /var/www/html/vendor/symfony/http-kernel/EventListener/RouterListener.php(114): Symfony\Component\Routing\Router-&gt;matchRequest(Object(Symfony\Component\HttpFoundation\Request))
#3 /var/www/html/vendor/symfony/event-dispatcher/EventDispatcher.php(212): Symfony\Component\HttpKernel\EventListener\RouterListener-&gt;onKernelRequest(Object(Symfony\Component\HttpKernel\Event\GetResponseEvent), 'kernel.request', Object(Symfony\Component\EventDispatcher\EventDispatcher))
#4 /var/www/html/vendor/symfony/event-dispatcher/EventDispatcher.php(44): Symfony\Component\EventDispatcher\EventDis in <b>/var/www/html/vendor/symfony/http-kernel/EventListener/RouterListener.php</b> on line <b>144</b><br />