public function getSpooler()
    {
        if (empty($this->spooler)) {
            $spool_class = $this->getDefault('spooler');
            if (class_exists($spool_class)) {
                $this->setSpooler(new $spool_class);
            } else {
                throw new \Exception(
                    sprintf('Default spool class "%s" not found!', $spool_class)
                );
            }
        }
        return $this->spooler;
    }