工作中一段時間對資料統計操作比較多，總結了部分常用到的Stream流操作。

1. 過濾並判空

      //String fundCode,List<GuaranteeSystemBIDataDetailStatistic> totalSealedStatistics 
       Optional<GuaranteeSystemBIDataDetailStatistic> totalSealedStatistic = totalSealedStatistics.stream().filter(statistic -> statistic.getFundCode().equals(fundCode)).findFirst();
        if(totalSealedStatistic.isPresent()){
            onLoanDataDetail.setTotalSealedNum(totalSealedStatistic.get().getTotalSealedNum());
        }
 

2. 求和(Stream複用)

 //List<AfterLoanDataDetail> afterLoanDataDetailList
 Supplier<Stream<AfterLoanDataDetail>> afterLoanDataDetailStream = () -> afterLoanDataDetailList.stream().filter(afterLoanDataDetail -> !FundCode.ZGC_BK.getCode().equals(afterLoanDataDetail.getFundCode()));
        Integer totalCompensatedNumSum = afterLoanDataDetailStream.get().collect(Collectors.summingInt(AfterLoanDataDetail::getTotalCompensatedNum));
        BigDecimal compensatedBalance = checkData(afterLoanDataDetailStream.get().map(AfterLoanDataDetail::getCompensatedBalance).reduce(BigDecimal.ZERO,BigDecimal::add));
 

3. 遍歷

   //List<AfterLoanDataDetailFormat> afterLoanDataDetailFormats
   afterLoanDataDetailFormats.forEach( detailFormat -> {
            if(!(ALL_FUND_CODE_CHARGE_GUARANTEE_AMOUNT.contains(detailFormat.getFundCode()))){
                detailFormat.setWjGuaranteeAmount("-");
                detailFormat.setYzGuaranteeAmount("-");
            }
        });
 

4. 排序

        List<RegionalRatio> regionalRatioList = new Gson().fromJson(request.getRatioData(),new TypeToken<List<RegionalRatio>>(){}.getType());
        List<RegionalRatio> regionalRatios = regionalRatioList.stream().filter(regionalRatio -> !TOTAL.equals(regionalRatio.getRegionCode())).collect(Collectors.toList());
        /* ---codes--- */
               case 1://正序
                        regionalRatios = regionalRatios.stream().sorted(Comparator.comparing(RegionalRatio::getOnLoanBalance)).collect(Collectors.toList());
                        break;
                    case 2://倒序
                        regionalRatios = regionalRatios.stream().sorted(Comparator.comparing(RegionalRatio::getOnLoanBalance).reversed()).collect(Collectors.toList());
                        break;
     

5. 集合合併

  //List<GuaranteeSystemBIDataDetailStatistic> onLoanBalanceList0,onLoanBalanceList
  //以ProvinceCode為id，id相同的進行LoanBanlanceAmount求和，即對onLoanBalanceList0進行去重合並
  onLoanBalanceList = onLoanBalanceList0.stream().collect(Collectors.toMap(GuaranteeSystemBIDataDetailStatistic::getProvinceCode,a->a,(o1,o2)->{
                o1.setLoanBanlanceAmount(o1.getLoanBanlanceAmount().add(o2.getLoanBanlanceAmount()));
                return o1;
            })).values().stream().collect(Collectors.toList());

6. 去重

        List<String> occupationList = allStatisticList.stream().map(statistic -> statistic.getOccupation()).distinct().collect(Collectors.toList());