@Override
  public String inputFormatClassName() {
    return inputFormatClassName;
  }
HiveInputSplit encapsulates an InputSplit with its corresponding
inputFormatClass. The reason that it derives from FileSplit is to make sure
"map.input.file" in MapTask.
ql/src/java/org/apache/hadoop/hive/ql/io/BucketizedHiveInputSplit.java