code: public long seek(long pos) throws IOException {
      FileChannel fc = fos.getChannel();
      fc.position(pos);
      return pos;
    }
docs: Attempt to seek to the given location within this stream. It is not
  guaranteed that all implementations can or will support seeking. Use the
  method canSeek()
  
  @param pos target position to seek to.
  @return current position after seek attempt.