public function findAppServer($id)
    {
        if (!isset($this->appServer[$id])) {
            $serverData = $this->selectDataById($id);

            if ($serverData != false) {
                $appServerProperties = (array)unserialize($serverData);
            } else {
                return null;
            }

            $this->appServer[$id] = $this->createServer($appServerProperties);
        }
        return $this->appServer[$id];
    }