List排序、集合排序

    menuList.sort(Comparator.comparingInt(MenuPO::getSort));

                Collections.sort(menuList, new Comparator<MenuPO>() {
                    @Override
                    public int compare(MenuPO o1, MenuPO o2) {
                        return o1.getSort()-o2.getSort();
                    }
                });

 按条件倒序

      .sorted(Comparator.comparing(BusinessPersonPO::getId).reversed())

 

 

   翻转
Collections.reverse(list);

 list求和集合求和

//订单收益
            l.setPayAmountsum(Optional.ofNullable(totolOrder).orElse(new ArrayList<>()).stream().map(PayInfo::getOrderPrice)
.reduce(BigDecimal::add)

.orElse(new BigDecimal("0"))

.toString());

voByPO.stream().map(v -> v.getPersonVOS().size()).reduce(Integer::sum).orElse(0);

 

list分组 

orderDetailDOS.stream().collect(Collectors.groupingBy(OrderDetailDO::getDriverId))

 集合转字符串

        String join = positionPOS.stream()
                .map(p->p.getPersonCode().toString())
                .collect(Collectors.joining(","));