@Override
  public void copyToExternalBuffer(byte[] externalBuffer, int externalBufferStart) {
    copyToBuffer(externalBuffer, externalBufferStart, currentExternalBufferNeededLen);
  }
Parse the byte[] and fill each field.

This is an adapted version of the parse method in the LazyStruct class.
They should parse things the same way.
serde/src/java/org/apache/hadoop/hive/serde2/lazy/fast/LazySimpleDeserializeRead.java