public static function getOssClient()
    {
        try {
            $ossClient = new OssClient(self::accessKeyId, self::accessKeySecret, self::endpoint, false);
        } catch (OssException $e) {
            printf(__FUNCTION__ . "creating OssClient instance: FAILED\n");
            printf($e->getMessage() . "\n");
            return null;
        }
        return $ossClient;
    }