lambda知识点【干货】

集合去重

字符串去重

List<String> dataList = list.stream().distinct().collect(Collectors.toList());

对象属性去重

根据品牌名称去重

List<Brand> brandList = brandList .stream().collect(Collectors.collectingAndThen(Collectors.toCollection(
                () -> new TreeSet<>(Comparator.comparing(Brand::getName))), ArrayList::new));

集合排序

排序的值不能为空，否则会报空指针异常

根据排序值升序排序

shopFloorFrontCategoryResponseList = shopFloorFrontCategoryResponseList.stream().filter(f->Objects.nonNull(f.getSort())).sorted(Comparator.comparing(ShopFloorFrontCategoryResponse::getSort)).collect(Collectors.toList());

根据排序值倒序排序

shopFloorFrontCategoryResponseList = shopFloorFrontCategoryResponseList.stream().filter(f->Objects.nonNull(f.getSort())).sorted(Comparator.comparing(ShopFloorFrontCategoryResponse::getSort).reversed()).collect(Collectors.toList());

获取集合中某个字段的最大值与最小值

最小值

Integer min = frontCategoryList.stream().mapToInt(FrontCategory::getSort).summaryStatistics().getMin();

最大值

Integer max = frontCategoryList.stream().mapToInt(FrontCategory::getSort).summaryStatistics().getMax();

获取集合中某个字段的和

Integer sum = frontCategoryList.stream().mapToInt(FrontCategory::getSort).sum();

分组

以categoryId分组

 Map<Long, List<FrontCategoryBack>> map = frontCategoryBackList.stream().
                filter(b -> Objects.nonNull(b.getCategoryId()))
                .collect(Collectors.groupingBy(FrontCategoryBack::getCategoryId));