public static Boolean getWriterDateProleptic(Map<String, String> metadata) {
    if (metadata == null) {
      return null;
    }
    String value = metadata.get(DataWritableWriteSupport.WRITER_DATE_PROLEPTIC);
    return value == null ? null : Boolean.valueOf(value);
  }
Get the proleptic from some metadata, otherwise return null.
ql/src/java/org/apache/hadoop/hive/ql/io/parquet/read/DataWritableReadSupport.java