public static void main(String[] args) {
        List<Member> list = getMemberList();
        // list去重
        list = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Member::getId))), ArrayList::new));
        // list排序 注册时间倒叙
        List<Member> memberSort = list.stream().sorted(Comparator.comparing(Member::getRegistrationDate).reversed()).collect(Collectors.toList());
        // list分组 根据会员等级分组
        Map<Integer, List<Member>> memberGroup = list.stream().collect(Collectors.groupingBy(Member::getLevel));
        // list取对象属性  会员姓名
        List<String> memberName = list.stream().map(Member::getName).distinct().collect(Collectors.toList());
        // list取两个属性  获取会员姓名及余额
        Map<String, BigDecimal> memberNameRemain = list.stream().collect(Collectors.toMap(Member::getName, Member::getRemainingSum));
        // 转map键不能重复 或为空
        Map<String, Member> memberInfo = list.stream().collect(Collectors.toMap(Member::getName, Function.identity(), (entity1, entity2) -> entity1));
        // list过滤 筛选余额不为0的
        List<Member> memberRemain = list.stream().filter(e -> (e.getRemainingSum() != null && !e.remainingSum.equals(new BigDecimal("0")))).collect(Collectors.toList());
        // list计算 计算总余额
        BigDecimal totalRemain = memberRemain.stream().map(Member::getRemainingSum).reduce(BigDecimal.ZERO, BigDecimal::add);
        //截取 取前2个会员
        List<Member> top2Members = list.stream().limit(2).collect(Collectors.toList());
        //截取 过滤掉前2个会员
        List<Member> skipTop2Members  = list.stream().skip(2).collect(Collectors.toList());

    }

    @Data
    static class Member {
        private Long id;
        private String name;
        private Integer level;
        private BigDecimal remainingSum;
        private Date registrationDate;
    }