parquet-hive/parquet-hive-storage-handler/src/main/java/org/apache/hadoop/hive/ql/io/parquet/convert/HiveSchemaConverter.java
private static GroupType convertMapType(final String name, final MapTypeInfo typeInfo) {
    final Type keyType = convertType(ParquetHiveSerDe.MAP_KEY.toString(),
        typeInfo.getMapKeyTypeInfo(), Repetition.REQUIRED);
    final Type valueType = convertType(ParquetHiveSerDe.MAP_VALUE.toString(),
        typeInfo.getMapValueTypeInfo());
    return ConversionPatterns.mapType(Repetition.OPTIONAL, name, keyType, valueType);
  }
private static GroupType convertMapType(final String name, final MapTypeInfo typeInfo) {
    final Type keyType = convertType(ParquetHiveSerDe.MAP_KEY.toString(),
        typeInfo.getMapKeyTypeInfo(), Repetition.REQUIRED);
    final Type valueType = convertType(ParquetHiveSerDe.MAP_VALUE.toString(),
        typeInfo.getMapValueTypeInfo());
    return ConversionPatterns.mapType(Repetition.OPTIONAL, name, keyType, valueType);
  }
2 elements: "key", "value"