namespace DrupalcontentRouting;

use DrupalCoreRoutingRouteSubscriberBase;
use SymfonyComponentRoutingRouteCollection;

/**
 * Listens to the dynamic route events.
 */
class RouteSubscriber extends RouteSubscriberBase {

  /**
   * Used to alter routes.
   */
  protected function alterRoutes(RouteCollection $collection) {
    if ($route = $collection->get('system.admin_content')) {
      $route->setDefaults(array(
        '_controller' => 'DrupalcontentControllerContentOverviewController::overview',
      ));
    }
  }

}

namespace DrupalcontentController;

use DrupalsystemControllerSystemController;

/**
 * Class ContentOverviewController.
 */
class ContentOverviewController extends SystemController {

  /**
   * Content Overview.
   */
  public function overview($link_id) {

    $build = [
      '#markup' => $this->t('Hello World!'),
    ];
    return $build;
  }

}

namespace DrupalcontentRouting

namespace DrupalmcontentRouting

services:
  content.route_subscriber:
    class: DrupalcontentRoutingRouteSubscriber
    tags:
      - { name: event_subscriber }