public static <M, OM> StreamOperatorSpec<M, OM> createMapOperatorSpec(
      MapFunction<? super M, ? extends OM> mapFn, String opId) {
    return new MapOperatorSpec<>((MapFunction<M, OM>) mapFn, opId);
  }
Creates a {@link StreamOperatorSpec} for {@link MapFunction}

@param mapFn  the map function
@param opId  the unique ID of the operator
@param <M>  type of input message
@param <OM>  type of output message
@return  the {@link StreamOperatorSpec}
samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpecs.java