Logging
The logger is present by default in the container. The app that is logging is set automatically.
The logger can be used in the following way:
<?php
namespace OCA\MyApp\Service;
use Psr\Log\LoggerInterface;
class AuthorService {
    private $logger;
    private $appName;
    public function __construct(LoggerInterface $logger, string $appName){
        $this->logger = $logger;
        $this->appName = $appName;
    }
    public function log($message) {
        $this->logger->error($message, ['extra_context' => 'my extra context']);
    }
}
The following methods are available:
- emergency 
- alert 
- critical 
- error 
- warning 
- notice 
- info 
- debug