code: @SuppressWarnings("unchecked")
    public void write(DataOutput out) throws IOException {
      if (conf == null) {
        throw new IOException("Hadoop Configuration not set via setConf");
      }
      WritableUtils.writeVInt(out, splits.size());
      for (InputSplit split : splits) {
        SplitUtil.serializeInputSplit(conf, (DataOutputStream) out, split);
      }
    }
docs: Write splits in the following format.
  {@code
  <count><class1><split1><class2><split2>...<classn><splitn>
  }