1. List Stream常用示例
1.条件筛选出List
List<CollectSummaryCost> parentItemList = summaryList.stream().filter(summaryCost -> Objects.equals(summaryCost.getId(), parentId)).collect(Collectors.toList());
2.筛选出List中的某个字段，形成新的集合
List<Long> deleteIdList = deleteList.stream().map(CollectArtificialCost::getId).collect(Collectors.toList());
3.使用聚合函数，筛选出最大值
CostCollectProjects lastCollectProject = oldCollectProjectsList.stream().max(Comparator.comparing(CostCollectProjects::getCreateTime)).get();
4.条件筛选出List中的某个实体
CollectSummaryCost firstHeadItem = list.stream().filter(item -> com.alibaba.druid.util.StringUtils.equals(item.getSno(), "一")).findAny().orElse(null);
5.筛选某个字段，形成string
String projectNames = submitCostProjectList.stream().map(CostCollectProjectsDto::getProjectName).collect(Collectors.joining(","));