Symfony2 listener to change the controller action based on whether it implements Cacheable or not

CacheControllerListener.php

<?php
namespace Acme\DemoBundle\Listener;

use Symfony\Component\HttpKernel\Event\FilterControllerEvent;
use Acme\DemoBundle\Controller\Cacheable;

class CacheControllerListener
{

    /**
     * This method will check if the controller implements Cacheable, if it does, it will check the last modified
     * date set on the controller and if the output is not modified will change the controller action
     * to output getLastModifiedResponse instead of the action it would otherwise have called
     *
     * @param FilterControllerEvent $event
     */
    public function onKernelController(FilterControllerEvent $event)
    {
        $controller = $event->getController();
        if (!is_array($controller)) {
            return;
        }

        $controllerObject = $controller[0];
        if ($controllerObject instanceof Cacheable) {
            if ($controllerObject->isNotModified($controllerObject->getLastModifiedDate())) {
                $controller[1] = 'getLastModifiedResponse';
            }
            $event->setController($controller);
        }
    }
}