DefaultController.php

<?php

namespace Drupal\badcamp\Controller;

use Drupal\Core\Controller\ControllerBase;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
use Drupal\ExtraModule\Annotation\Permission;
use Drupal\Core\Template\TwigEnvironment;

class DefaultController extends ControllerBase implements ContainerInjectionInterface {

  /**
   * @var \TwigEnvironment
   */
  protected $twig;

  public function __construct(TwigEnvironment $twig) {
    $this->twig = $twig;
  }

  public static function create(ContainerInterface $container){
    return new static(
      $container->get('twig')
    );
  }

  /**
   * helloAction
   * @param  string $name Get
   * @return [type]       [description]
   *
   * @Permission("access content")
   */
  public function helloAction($name) {

    $template = $this->twig->loadTemplate('badcamp::hello.html.twig');

    return $template->render(array(
      'name' => $name
    ));
  }

}