java使用stream()中的reducing实现将名字相同的累加(合并)点餐数量的，早餐，午餐，晚餐(分组计算)

墨蓝 2024-03-23 21:33 19阅读 0赞

### java使用stream()中的reducing实现将名字相同的累加(合并)点餐数量的，早餐，午餐，晚餐 ###

//	方法一
    		Map<String, PersonFamilyFoodOrderDTO> mergedOrders = personFamilyFoodOrderDTOList.stream()
                    .collect(Collectors.groupingBy(PersonFamilyFoodOrderDTO::getUserName, Collectors.reducing(SysFoodOrderController::mergeOrder)))
                    .entrySet()
                    .stream()
                    .collect(Collectors.toMap(Map.Entry::getKey, e -> e.getValue().orElse(null)));
            List<PersonFamilyFoodOrderDTO> collect = mergedOrders.values().stream()
                    .collect(Collectors.toList());
                    
            //	方法二
            List<Optional<PersonFamilyFoodOrderDTO>> collect1 = personFamilyFoodOrderDTOList.stream()
                    .collect(Collectors.groupingBy(PersonFamilyFoodOrderDTO::getUserName,
                            Collectors.reducing(SysFoodOrderController::mergeOrder)))
                    .values().stream().collect(Collectors.toList());
    
    
    		private static PersonFamilyFoodOrderDTO mergeOrder(PersonFamilyFoodOrderDTO o1, PersonFamilyFoodOrderDTO o2) {
        
            return new PersonFamilyFoodOrderDTO(o1.getUserName(),
                    o1.getBreakfast() + o2.getBreakfast(),
                    o1.getLunch() + o2.getLunch(),
                    o1.getDinner() + o2.getDinner(),
                    o1.getFamilyBreakfast() + o2.getFamilyBreakfast(),
                    o1.getFamilyLunch() + o2.getFamilyLunch(),
                    o1.getFamilyDinner() + o2.getFamilyDinner()
                    );
        }

### 通过分组foodMenuDate,foodMenuType来统计OrderNumber总数 ###

Map<String, Integer> sums = sysFoodOrderList.stream()
                   .collect(Collectors.groupingBy(p -> p.getFoodMenuDate() + "-" + p.getFoodMenuType()
                   ,Collectors.summingInt(SysFoodOrder::getOrderNumber)));