drupal 8 pass variable to controller without seting it tourl code example

Example: drupal 8 routing parameters

example.user:
  path: '/example/{user}'
  defaults: 
    _controller: '\Drupal\example\Controller\ExampleController::content' 
  requirements: 
    _permission: 'access content' 
  options:
    parameters:
      user:
        type: entity:user