@Override
  public Iterator<HCatRecord> read() throws HCatException {

    HCatInputFormat inpFmt = new HCatInputFormat();
    RecordReader<WritableComparable, HCatRecord> rr;
    try {
      TaskAttemptContext cntxt = ShimLoader.getHadoopShims().getHCatShim().createTaskAttemptContext(conf, new TaskAttemptID());
      rr = inpFmt.createRecordReader(split, cntxt);
      rr.initialize(split, cntxt);
    } catch (IOException e) {
      throw new HCatException(ErrorType.ERROR_NOT_INITIALIZED, e);
    } catch (InterruptedException e) {
      throw new HCatException(ErrorType.ERROR_NOT_INITIALIZED, e);
    }
    return new HCatRecordItr(rr);
  }
This reader reads via {@link HCatInputFormat}
hcatalog/core/src/main/java/org/apache/hive/hcatalog/data/transfer/impl/HCatInputFormatReader.java