private ColumnVector getChildData(ListColumnVector lcv, int index) {
    if (lcv.offsets[index] > Integer.MAX_VALUE || lcv.lengths[index] > Integer.MAX_VALUE) {
      throw new RuntimeException("The element number in list is out of scope.");
    }
    if (lcv.isNull[index]) {
      return null;
    }
    int start = (int)lcv.offsets[index];
    int length = (int)lcv.lengths[index];
    ColumnVector child = lcv.child;
    ColumnVector resultCV = null;
    if (child instanceof LongColumnVector) {
      resultCV = new LongColumnVector(length);
      try {
        System.arraycopy(((LongColumnVector) lcv.child).vector, start,
            ((LongColumnVector) resultCV).vector, 0, length);
      } catch (Exception e) {
        throw new RuntimeException(
            "Fail to copy at index:" + index + ", start:" + start + ",length:" + length + ",vec " +
                "len:" + ((LongColumnVector) lcv.child).vector.length + ", offset len:" + lcv
                .offsets.length + ", len len:" + lcv.lengths.length, e);
      }
    }
    if (child instanceof DoubleColumnVector) {
      resultCV = new DoubleColumnVector(length);
      System.arraycopy(((DoubleColumnVector) lcv.child).vector, start,
          ((DoubleColumnVector) resultCV).vector, 0, length);
    }
    if (child instanceof BytesColumnVector) {
      resultCV = new BytesColumnVector(length);
      System.arraycopy(((BytesColumnVector) lcv.child).vector, start,
          ((BytesColumnVector) resultCV).vector, 0, length);
    }
    if (child instanceof DecimalColumnVector) {
      resultCV = new DecimalColumnVector(length,
          ((DecimalColumnVector) child).precision, ((DecimalColumnVector) child).scale);
      System.arraycopy(((DecimalColumnVector) lcv.child).vector, start,
          ((DecimalColumnVector) resultCV).vector, 0, length);
    }
    System.arraycopy(lcv.child.isNull, start, resultCV.isNull, 0, length);
    return resultCV;
  }
Get the child ColumnVector of ListColumnVector
ql/src/java/org/apache/hadoop/hive/ql/io/parquet/vector/VectorizedListColumnReader.java