protected function getCachedUrlFileName($url, &$urlList)
    {
        $key = $this->getUrlListCacheKey();
        $urlList = Cache::get($key, false);

        if ($urlList
            && ($urlList = @unserialize(@base64_decode($urlList)))
            && is_array($urlList)
            && array_key_exists($url, $urlList)
        ) {
            return $urlList[$url];
        }

        return null;
    }