code: public InputSplit[] getSplits(JobConf job, int numSplits) throws IOException {
      setFormat(job);
      job.setLong("mapred.min.split.size", Long.MAX_VALUE);
      return root.getSplits(job, numSplits);
    }
docs: Build a CompositeInputSplit from the child InputFormats by assigning the
  ith split from each child to the ith composite split.