Pimcore\Log\ApplicationLogger::addWriter PHP Method

    public function addWriter($writer)
    {
        if ($writer instanceof \Zend_Log_Writer_Abstract) {
            // ZF compatibility
            if (!isset($this->loggers["default-zend"])) {
                // auto init Monolog logger
                $this->loggers["default-zend"] = new \Zend_Log();
            }
            $this->loggers["default-zend"]->addWriter($writer);
        } elseif ($writer instanceof \Monolog\Handler\HandlerInterface) {
            if (!isset($this->loggers["default-monolog"])) {
                // auto init Monolog logger
                $this->loggers["default-monolog"] = new \Monolog\Logger('app');
            }
            $this->loggers["default-monolog"]->pushHandler($writer);
        } elseif ($writer instanceof \Psr\Log\LoggerInterface) {
            $this->loggers[] = $writer;
        }
    }