code: @SuppressWarnings("unchecked")
      public static <K1, V1, K2, V2> Class<BaseMapper<K1, V1, K2, V2>> getMapperClass(
          JobContext job) {
      	Configuration conf = job.getConfiguration();
          return (Class<BaseMapper<K1, V1, K2, V2>>)conf.getClass(
          		ConfigConstants.CONF_MULTITHREADEDMAPPER_CLASS, BaseMapper.class);
      }
docs: Get the application's mapper class.
  
  @param <K1>
  the map's input key type
  @param <V1>
  the map's input value type
  @param <K2>
  the map's output key type
  @param <V2>
  the map's output value type
  @param job
  the job
  @return the mapper class to run