For importing Request Class use following statement
use SymfonyComponentHttpFoundationRequest;

Following statement creates object of class “Request”
$request = Request::createFromGlobals();

// the URI being requested (e.g. /about) minus any query parameters
Every Index of $_SERVER global variable can be accessed using Request object with using get method
so for example to get $_SERVER['PATH_INFO'] using Request Object use following statement.

$request->getPathInfo();

// retrieve GET and POST variables respectively
$request->query->get(‘foo’);
$request->request->get(‘bar’);

// retrieves an instance of UploadedFile identified by foo
$request->files->get(‘foo’);

$request->getMethod(); // GET, POST, PUT, DELETE, HEAD
$request->getLanguages(); // an array of languages the client accepts

List of functions available in Request class can be accessed via following link

http://api.symfony.com/2.0/Symfony/Component/HttpFoundation/Request.html