Short snippet that shows how to get url parameters in drupal 8.
to get query parameter form the url, you can us the following.
If you have the url for example /page?uid=123&num=452
To get all params, use:
$param = \Drupal::request()->query->all();
To get "uid" from the url, use:
$uid = \Drupal::request()->query->get('uid');
To get "num" from the url, use:
$num = \Drupal::request()->query->get('num');
