symfony as a microframework

app.php

<?php

use Symfony\Component\HttpFoundation\Request;
use App\AppKernel;

$loader = require_once __DIR__.'/../vendor/autoload.php';

$kernel = new AppKernel();
$request = Request::createFromGlobals();
$response = $kernel->handle($request);
$response->send();
$kernel->terminate($request, $response);

AppKernel.php

<?php

namespace App;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\HttpKernel;
use Symfony\Component\HttpKernel\HttpKernelInterface;

class AppKernel extends HttpKernel
{
    public function __construct() {}

    public function handle(Request $request, $type = HttpKernelInterface::MASTER_REQUEST, $catch = true)
    {
        switch ($request->getPathInfo()) {
            case '/cache':
                $response = new Response(microtime(true));
                $response->setCache(array('max_age' => 3600, 'public' => true));

                return $response;
            case '/negotiation':
                $response = new Response(microtime(true));
                $response->setCache(array('max_age' => 3600, 'public' => true));
                $response->headers->set('Content-Type', $_SERVER['HTTP_ACCEPT']);
                $response->setVary('Accept');

                return $response;
        }

        return new Response('Unknown request '.$request->getPathInfo(), 404);
    }
}

Neat! That's the true power of Symfony: awesome reusable components!

@dbu why are you extending HttpKernel ? You never use it. Just implement the HttpKernelInterface directly.