public Transfer writeBytes(byte[] data) throws IOException {
  if (data == null) {
    writeInt(-1);
  }
 else {
    writeInt(data.length);
    out.write(data);
  }
  return this;
}

public Transfer writeBytes ( byte [ ] data ) throws IOException { if ( data == null ) { writeInt ( - 1 ) ; } else { writeInt ( data . length ) ; out . write ( data ) ; } return this ; }
write a byte array .
