code: public static final DefaultTupleMapper newBinaryDefaultTupleMapper( ) {
          return new DefaultTupleMapper(new TupleMapper<String>() {
              @Override
              public String map(Tuple input) {
                  try {
                      return new String(input.getBinaryByField(FIELD_SOURCE), "UTF-8");
                  } catch (UnsupportedEncodingException e) {
                      throw new MappingException("Error while processing source as a byte[]", e);
                  }
              }
          });
      }
docs: Returns a new {@link DefaultTupleMapper} that accept Byte[] as source field value.