stream流

去重

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List<String> orderNoList = inOutWarehouseRecordMap.values().stream()
        .map(InOutWarehouseRecord::getOrderNo)
        .distinct()
        .collect(Collectors.toList());

将value为集合的map转化为list

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//Map<Long, List<RecordGoodsDetail>> goodsDetailMap
List<RecordGoodsDetail> allDetails = goodsDetailMap.values().stream()      .flatMap(List::stream).collect(Collectors.toList());

常用构造方式

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List<SuppliedMaterialsDTO> suppliedMaterialsDTOList = records.stream().map(inOutWarehouseRecord -> {
           return SuppliedMaterialsDTO.builder()
                   //......
                   .build();
       }).collect(Collectors.toList());

根据集合的某一个字段（比如id），进行分类，计算其中的几个属性累加值

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//相同的进行累加
Map<Long, OrderReturnMaterialsDTO> mergedMap = orderReturnMaterialsDTOList.stream()
        .collect(Collectors.toMap(
                OrderReturnMaterialsDTO::getGoodsDetailId,
                dto -> dto,
                (dto1, dto2) -> OrderReturnMaterialsDTO.builder()
                        .goodsDetailId(dto1.getGoodsDetailId())
                        .categorize(dto1.getCategorize())
                        .type(dto1.getType())
                        .name(dto1.getName())
                        .goodsModel(dto1.getGoodsModel())
                        .returnNumber(dto1.getReturnNumber().add(dto2.getReturnNumber()))
                        .build()
        ));
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//相同的进行累加
Map<Long, OrderSuppliedMaterialsDTO> mergedMap = orderSuppliedMaterialsDTOList.stream()
        .collect(Collectors.toMap(
                OrderSuppliedMaterialsDTO::getGoodsDetailId,
                dto -> dto,
                (dto1, dto2) -> OrderSuppliedMaterialsDTO.builder()
                        .id(dto1.getId())
                        .goodsDetailId(dto1.getGoodsDetailId())
                        .categorize(dto1.getCategorize())
                        .type(dto1.getType())
                        .name(dto1.getName())
                        .goodsModel(dto1.getGoodsModel())
                        .receiveNumber(dto1.getReceiveNumber().add(dto2.getReceiveNumber()))
                        .returnNumber(dto1.getReturnNumber().add(dto2.getReturnNumber()))
                        .transferInNumber(dto1.getTransferInNumber().add(dto2.getTransferInNumber()))
                        .transferOutNumber(dto1.getTransferOutNumber().add(dto2.getTransferOutNumber()))
                        .build()
        ));