@Override
  public int getListLength(final Object data) {
    if (data == null) {
      return -1;
    }

    if (data instanceof ArrayWritable) {
      final Writable[] array = ((ArrayWritable) data).get();
      if (array == null) {
        return -1;
      }

      return array.length;
    }

    if (data instanceof List) {
      return ((List<?>)data).size();
    }

    throw new UnsupportedOperationException("Cannot inspect " + data.getClass().getCanonicalName());
  }
The ParquetHiveArrayInspector will inspect an ArrayWritable, considering it as an Hive array.<br>
It can also inspect a List if Hive decides to inspect the result of an inspection.
ql/src/java/org/apache/hadoop/hive/ql/io/parquet/serde/ParquetHiveArrayInspector.java