core/src/main/java/com/twitter/elephantbird/mapreduce/input/combine/CompositeInputSplit.java
@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);
    }
  }
@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);
    }
  }
Write splits in the following format.
{@code
<count><class1><split1><class2><split2>...<classn><splitn>
}