private function getFileName($key)
{
$md5Key = md5($this->conf['prefix'] . $key);
$dir = $this->conf['CACHE_PATH'] . substr($key, 0, strrpos($key, '/')) . DIRECTORY_SEPARATOR;
$dir .= substr($md5Key, 0, 2) . DIRECTORY_SEPARATOR . substr($md5Key, 2, 2);
is_dir($dir) || mkdir($dir, 0700, true);
return $dir . DIRECTORY_SEPARATOR . $md5Key . '.php';
}