stream使用汇总

整理了下java使用stream处理list的几个便捷的方法

准备数据

 List<KnowledgeInfoTable> knowledgeInfoTables = knowledgeInfoMapper.selectAllEffective();

• 提取ids

List<Long> collect = knowledgeInfoTables.stream().map(KnowledgeInfoTable::getKnowledgeInfoId).collect(Collectors.toList());

• 过滤

List<KnowledgeInfoTable> collect = knowledgeInfoTables.stream().
filter(e -> e.getKnowledgeInfoId() != 473730496668160L).collect(Collectors.toList());

• 组map

 Map<Long, Long> collect = knowledgeInfoTables.stream().collect(Collectors.toMap(KnowledgeInfoTable::getKnowledgeInfoId, KnowledgeInfoTable::getSubjectId));

组groupBy

Map<Long, List<KnowledgeInfoTable>> collect = knowledgeInfoTables.stream().collect(Collectors.groupingBy(KnowledgeInfoTable::getKnowledgeInfoId));

先转其他dto，然后抽出取id为键名，dto为键值

Map<String, CollectDetailResponseDTO> newsByIdCollect = new HashMap<>();
newsByIdCollect = newsById.getData().stream().map(newsResponseDTO -> getCollectDetailResponseDTO(newsResponseDTO))
        .collect(Collectors.toMap(CollectDetailResponseDTO::getId, collectDetailResponseDTO -> collectDetailResponseDTO, (v1, v2) -> v2));