val userDatumReader : DatumReader[User] = new SpecificDatumReader[User](User.class);
val dataFileReader : DataFileReader[User] = new DataFileReader[User](file, userDatumReader);

def dataFileReaderToIterator[T](dataFileReader : DataFileReader[T]) : Iterator[T] =
  new Iterator[T] {
    override def hasNext : Boolean = dataFileReader.hasNext

    override def next() : T = dataFileReader.next
  }

val userSource : Source[User, _] =
  Source.fromIterator(() => dataFileReaderToIterator(dataFileReader))