Detectar peticiones AJAX con Symfony

detect-ajax-request-symfony.php

<?php
namespace AppBundle\Controller;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class DefaultController extends Controller
{
    /**
     * @Route("/", name="homepage")
     */
    public function indexAction(Request $request)
    {
        //Aquí calculariamos el contenido 
      
        //Si es una peticion ajax
        if( $request->isXmlHttpRequest() ) {
          return $this->render('index.json.twig');
        }
      
        return $this->render('index.html.twig');
    }
}