JAVA8 Stream()遍歷求某列總和

List<CommonExportDTO> commonList;
// 取字段string轉int構建新列表
List<Integer> collect = commonList.stream().map(dto -> Integer.valueOf(dto.getCell6())).collect(Collectors.toList());
// reduce求和
Optional<Integer> reduce = collect.stream().reduce(Integer::sum);
Integer total = reduce.get();