public OutputCollector getMapperCollector(int mapperIndex,

                                            OutputCollector output,

                                            Reporter reporter) {

    Serialization keySerialization = mappersKeySerialization.get(mapperIndex);

    Serialization valueSerialization =

      mappersValueSerialization.get(mapperIndex);

    return new ChainOutputCollector(mapperIndex, keySerialization,

                                    valueSerialization, output, reporter);

  }