JAVA8：stream流

List<SystemCodeDataDTO> systemCodeDataDTOList = Optional.ofNullable(data).map(JSON::parseArray).map(d -> d.toJavaList(SystemCodeDataDTO.class))
                .map(List::stream).map(s -> s.filter(SystemCodeDataDTO::getProductLevel)).map(s -> s.collect(Collectors.toList())).orElseGet(ArrayList::new);

一、List对象拆分

//1. 根据对象属性进行分组
Map<String, List<Order>> orderMap = orderListAll.stream().collect(Collectors.groupingBy(Order::getProdProductId));
//2. 根据对象中的对象属性进行分组
Map<String, List<BagItem>> orderMap = bagItemList.stream().collect(Collectors.groupingBy(bagItem -> bagItem.getBag().getId()));
//3. 根据对象属性进行分组，且只映射出对象某个属性的列表
Map<String, List<String>> orderClearanceIdMap = orderClearanceAllList.stream().collect(Collectors.groupingBy(OrderClearance::getValuationType, Collectors.mapping(OrderClearance::getId, Collectors.toList())));
//4. 分组后排序取最新测试时间的记录
Map<String, CalibrateCheckResult> calibrateCheckResultMap = calibrateCheckResultList.stream().collect(Collectors.groupingBy(i -> i.getProcess(), Collectors.collectingAndThen(Collectors.reducing((c1, c2) -> c1.getTestTime().compareTo(c2.getTestTime()) >= 0 ? c1 : c2), Optional::get)));

二、按条件筛选List

//按条件筛选
List list = list.stream().filter(l -> l.getName().equals("x")).collect(Collectors.toList());
//是否存在满足条件的元素    anyMatch:任意一个    allMatch:所有    noneMatch:没有一个
Boolean b = list.stream().anyMatch(clearGoods -> clearGoods.getName().equals("a"));

三、将对象某个属性转List

List<String> idList = logisticsFinanceDayOrderList.stream().map(LogisticsFinanceDayOrder::getId).collect(Collectors.toList());

四、将对象某个属性拼接为String

String chargeTypeStr = financeOrderItemExpenses.stream().map(FinanceOrderItemExpense::getChargeType).distinct().collect(Collectors.joining(","));

五、对象属性加减乘除

//将对象某个属性（Integer）求和
Integer count = customerGoodsMessageVOList.stream().mapToInt(CustomerGoodsMessageVO::getCount).sum();
//将对象某个属性（Float）求和
Float totalWeight = financeOrderList.stream().map(CustomerFinanceOrder::getWeight).reduce(Float::sum).get();
//将对象某个属性（BigDecimal）求和
BigDecimal totalPrice1 = financeOrderList.stream().map(CustomerFinanceOrder::getBeforeDiscountPrice).reduce(BigDecimal::add).get();

六、List转Map

Map<String, String> map = platformIncomeWithdrawFianceHistoryDao.getDistinctAccountType().stream().collect(Collectors.toMap(String::toString, s -> s));

Map<String, String> map = list.stream().collect(Collectors.toMap(item -> item.get("value"), item -> item.get("label")));

七、Map转List

//将Map的Key转成List
List passIdList = map.entrySet().stream().filter(s -> s.getValue().equals("a")).map(Map.Entry::getKey).collect(Collectors.toList());

八、按对象某个属性去重

List<ChannelApplication> unique = channelApplicationList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(ChannelApplication::getApplicationName))), ArrayList::new));

九、普通操作

//循环添加
exportExcelTemplateItemList.stream().forEach(exportExcelTemplateItem -> exportList.add(exportExcelTemplateItem));
//每个元素均执行某个方法
List<AddOrUpdatePluginInfoVO> addOrUpdatePluginInfoVOList = records.stream().map(this::convertOne).collect(Collectors.toList());
//元素拆分后合并成List
List<Long> mediumIdList = channelPromotionVOList.stream().map(ChannelPromotionVO::getMediumId).distinct().map(m -> StrUtil.split(m, ",")).flatMap(Arrays::stream).filter(StrUtil::isNotEmpty).map(Long::parseLong).collect(Collectors.toList());

十、其它

dataGrid.getRows().stream().skip((pageNo - 1) * pageSize).limit(pageSize).forEach(e -> currentPageData.add(e));

//先根据“条件优先级配置”的优先级分组，再排序获取优先级最高，再根据“产品谱系”中的层级优先级排序（产品型号 < 产品系列 < 产品类型）
StepWarningStandard stepWarningStandard = stepWarningStandardList
        .stream().collect(Collectors.groupingBy(i -> i.getPriorityElementConfig().getPriority())).entrySet()
        .stream().sorted(Map.Entry.<Integer, List<StepWarningStandard>>comparingByKey()).findFirst().get().getValue()
        .stream().sorted(Comparator.comparing(i -> i.getPedigree().getType())).reduce((first, second) -> second).get();

 [{"0":"a","1":"b"},{"0":"a1","1":"b1"}] -> {a:b,a1:b2}