class RouteSubscriber

1. 8.x drupal/core/modules/views/lib/Drupal/views/EventSubscriber/RouteSubscriber.php \Drupal\views\EventSubscriber\RouteSubscriber
2. 8.x drupal/core/modules/field_ui/lib/Drupal/field_ui/Routing/RouteSubscriber.php \Drupal\field_ui\Routing\RouteSubscriber
3. 8.x drupal/core/modules/rest/lib/Drupal/rest/EventSubscriber/RouteSubscriber.php \Drupal\rest\EventSubscriber\RouteSubscriber

field_ui.services.yml in drupal/core/modules/field_ui/field_ui.services.yml

drupal/core/modules/field_ui/field_ui.services.yml

field_ui.subscriber in drupal/core/modules/field_ui/field_ui.services.yml

Drupal\field_ui\Routing\RouteSubscriber

class RouteSubscriber implements EventSubscriberInterface {

  /**
   * The entity type manager
   *
   * @var \Drupal\Core\Entity\EntityManager
   */
  protected $manager;

  /**
   * Constructs a RouteSubscriber object.
   *
   * @param \Drupal\Core\Entity\EntityManager $manager
   *   The entity type manager.
   */
  public function __construct(EntityManager $manager) {
    $this->manager = $manager;
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $events[RoutingEvents::DYNAMIC] = 'routes';
    return $events;
  }

  /**
   * Adds routes for the Field UI.
   */
  public function routes(RouteBuildEvent $event) {
    $collection = $event
      ->getRouteCollection();
    foreach ($this->manager
      ->getDefinitions() as $entity_type => $entity_info) {
      $defaults = array();
      if ($entity_info['fieldable'] && isset($entity_info['route_base_path'])) {
        $path = $entity_info['route_base_path'];
        $route = new Route("{$path}/fields/{field_instance}", array(
          '_form' => '\\Drupal\\field_ui\\Form\\FieldInstanceEditForm',
        ), array(
          '_permission' => 'administer ' . $entity_type . ' fields',
        ));
        $collection
          ->add("field_ui.instance_edit.{$entity_type}", $route);
        $route = new Route("{$path}/fields/{field_instance}/field", array(
          '_form' => '\\Drupal\\field_ui\\Form\\FieldEditForm',
        ), array(
          '_permission' => 'administer ' . $entity_type . ' fields',
        ));
        $collection
          ->add("field_ui.field_edit.{$entity_type}", $route);
        $route = new Route("{$path}/fields/{field_instance}/widget-type", array(
          '_form' => '\\Drupal\\field_ui\\Form\\FieldWidgetTypeForm',
        ), array(
          '_permission' => 'administer ' . $entity_type . ' fields',
        ));
        $collection
          ->add("field_ui.widget_type.{$entity_type}", $route);
        $route = new Route("{$path}/fields/{field_instance}/delete", array(
          '_form' => '\\Drupal\\field_ui\\Form\\FieldDeleteForm',
        ), array(
          '_permission' => 'administer ' . $entity_type . ' fields',
        ));
        $collection
          ->add("field_ui.delete.{$entity_type}", $route);

        // If the entity type has no bundles, use the entity type.
        $defaults['entity_type'] = $entity_type;
        if (empty($entity_info['entity_keys']['bundle'])) {
          $defaults['bundle'] = $entity_type;
        }
        $route = new Route("{$path}/fields", array(
          '_form' => '\\Drupal\\field_ui\\FieldOverview',
        ) + $defaults, array(
          '_permission' => 'administer ' . $entity_type . ' fields',
        ));
        $collection
          ->add("field_ui.overview.{$entity_type}", $route);
        $route = new Route("{$path}/display", array(
          '_form' => '\\Drupal\\field_ui\\DisplayOverview',
        ) + $defaults, array(
          '_permission' => 'administer ' . $entity_type . ' display',
        ));
        $collection
          ->add("field_ui.display_overview.{$entity_type}", $route);
        foreach (entity_get_view_modes($entity_type) as $view_mode => $view_mode_info) {
          $route = new Route("{$path}/display/{$view_mode}", array(
            '_form' => '\\Drupal\\field_ui\\DisplayOverview',
            'view_mode' => $view_mode,
          ) + $defaults, array(
            '_field_ui_view_mode_access' => 'administer ' . $entity_type . ' display',
          ));
          $collection
            ->add("field_ui.display_overview.{$entity_type}.{$view_mode}", $route);
        }
      }
    }
  }

}