parquet-column/src/main/java/org/apache/parquet/column/values/delta/DeltaBinaryPackingValuesWriterForLong.java
@Override
  public BytesInput getBytes() {
    // The Page Header should include: blockSizeInValues, numberOfMiniBlocks, totalValueCount
    if (deltaValuesToFlush != 0) {
      flushBlockBuffer();
    }
    return BytesInput.concat(
            config.toBytesInput(),
            BytesInput.fromUnsignedVarInt(totalValueCount),
            BytesInput.fromZigZagVarLong(firstValue),
            BytesInput.from(baos));
  }
@Override
  public BytesInput getBytes() {
    // The Page Header should include: blockSizeInValues, numberOfMiniBlocks, totalValueCount
    if (deltaValuesToFlush != 0) {
      flushBlockBuffer();
    }
    return BytesInput.concat(
            config.toBytesInput(),
            BytesInput.fromUnsignedVarInt(totalValueCount),
            BytesInput.fromZigZagVarLong(firstValue),
            BytesInput.from(baos));
  }
getBytes will trigger flushing block buffer, DO NOT write after getBytes() is called without calling reset()

@return a BytesInput that contains the encoded page data