Catch-all route in Symfony 3 - php

Question

I have a catch-all fallback route in Symfony2 that I couldn't get to work in Symfony3. I tried this exact syntax (a verbatim copy of my Symfony2 route) and that didn't work.
fallback:
path: /{req}
defaults: { _controller: MyBundle:Default:catchAll }
requirements:
req: ".+"
How can I get this working in Symfony3? (It's literally the only thing holding me back from using Symfony3 and keeping me at v2.8)

Answer 1

This should help you:
route1:
path: /{req}
defaults: { _controller: 'AppBundle:Default:index' }
requirements:
req: ".+"
Where, my controller is called "DefaultController", and I have a function called "indexAction()".
Here is my code for the DefaultController:
class DefaultController extends Controller
{
/**
* #Route("/", name="homepage")
*/
public function indexAction(Request $request)
...
I actually did try what you said in my environment, and it didn't work until I had the right controller settings specified.
EDIT:
For this to work, it was necessary to add the parameter Request $request (with the type hint) to the action's method signature.

Answer 2

I found the current accepted answer almost useful for Symfony 4, so I'm going to add my solution:
This is what I did to get it working in Symfony 4:
Open /src/Controller/DefaultController.php, make sure there is a function called index(){}
It's not required to add the Request $request as first param as some comment suggest.
This is the method that will handle all urls caught by the routes.yaml
Open /config/routes.yaml, add this:
yourRouteNameHere:
path: /{req}
defaults: { _controller: 'App\Controller\DefaultController::index' }
requirements: # the controller --^ the method --^
req: ".*"` # not ".+"

Answer 3

You can also override Exception controller.
# app/config/config.yml
twig:
exception_controller: app.exception_controller:showAction
# app/config/services.yml
services:
app.exception_controller:
class: AppBundle\Controller\ExceptionController
arguments: ['#twig', '%kernel.debug%']
namespace AppBundle\Controller;
use Symfony\Component\Debug\Exception\FlattenException;
use Symfony\Component\HttpKernel\Log\DebugLoggerInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
class ExceptionController
{
protected $twig;
protected $debug;
public function __construct(\Twig_Environment $twig, $debug)
{
$this->twig = $twig;
$this->debug = $debug;
}
public function showAction(Request $request, FlattenException $exception, DebugLoggerInterface $logger = null)
{
// some action
return new Response($this->twig->render('error/template.html.twig', [
'status_code' => $exception->getStatusCode()
]
));
}
}