presto-orc/src/main/java/io/prestosql/orc/OrcRecordReader.java/OrcRecordReader/createColumnReaders
class OrcRecordReader:    private ColumnReader[] createColumnReaders(
            List<OrcColumn> columns,
            List<Type> readTypes,
            AggregatedMemoryContext systemMemoryContext,
            OrcBlockFactory blockFactory)
            throws OrcCorruptionException
    {
        ColumnReader[] columnReaders = new ColumnReader[columns.size()];
        for (int i = 0; i < columns.size(); i++) {
            int columnIndex = i;
            Type readType = readTypes.get(columnIndex);
            OrcColumn column = columns.get(columnIndex);
            columnReaders[columnIndex] = createColumnReader(readType, column, systemMemoryContext, blockFactory);
        }
        return columnReaders;
    }