code: public static final DataTransferThrottler getThrottler(Configuration conf, 
        boolean disableThrottler) {
      if (disableThrottler) {
        return null;
      }
      long transferBandwidth = 
        conf.getLong(HdfsConstants.DFS_IMAGE_TRANSFER_RATE_KEY,
            HdfsConstants.DFS_IMAGE_TRANSFER_RATE_DEFAULT);
      DataTransferThrottler throttler = null;
      if (transferBandwidth > 0) {
        throttler = new DataTransferThrottler(transferBandwidth);
      }
      return throttler;
    }
docs: Construct a throttler from conf
  @param conf configuration
  @return a data transfer throttler