public static <M> StreamOperatorSpec<M, M> createFilterOperatorSpec(
      FilterFunction<? super M> filterFn, String opId) {
    return new FilterOperatorSpec<>((FilterFunction<M>) filterFn, opId);
  }
Creates a {@link StreamOperatorSpec} for {@link FilterFunction}

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