If you have a habit of using an ORM inspired by the "active record" design pattern and you have switched to Symfony 3, you will be surprised that you cannot use a service (the logger for example) in an entity.
Indeed, nothing can be found other than the attributes and the business layer in the Symfony 3 entities.
In order to be able to use a service and to avoid having to repeat each action of the controller, you have to create a service (in which one has access to the other services).

To begin, you must define this service in the services.yml file located in the app/config directory:

services:
     submission_file_saver:
        class: AppBundle\Service\SubmissionFileSaver
        arguments: ["@logger"]

Here we declare the service "SubmissionFileSaver" and we want to inject the service "logger".

We create our class "SubmissionFileSaver" and this one will have the following constructor:

public function __construct(LoggerInterface $logger)
  {
    $this->logger = $logger;
  }

We add one or more methods that will use this logger:

public function saveFiles($submission, $prefix = null) {
    try {
      //save file with $submission data
    } catch (\Exception $exception) {
      $this->logger->error($exception->getMessage());
    }
  }

We can now inject and use this service in our actions of our controller:

public function registerAction(Request $request, SubmissionFileSaver $file_saver)
{
    $submission = new Submission();
    ...

    $file_saver->saveFiles($submission, $prefix);
    ...
    
}