code: protected function createCacheFilePath($key)
      {
          $folderSufix = sprintf('%03d', hexdec(substr(sha1($key), -5)) % 1000);
          $cacheFolder = $this->createCacheFileFolder() . DIRECTORY_SEPARATOR . $folderSufix;
          if (!is_dir($cacheFolder)) {
              mkdir($cacheFolder, 0777, true);
          }
  
          return $cacheFolder . DIRECTORY_SEPARATOR . md5($key) . '.dat';
      }
docs: 考虑到Linux同一目录下的文件个数限制，这里拆分成1000个文件缓存目录
  
  @param string $key 缓存key
  @return string 路径