Java Stream流实现递归查询

MySql数据库表结构

模拟数据

查询出所有数据，用父节点递归查询出所有子节点数据

  /**
     * 封装备注分类集合
     *
     * @param remarkTypeList 备注分类集合
     * @return 递归好的集合
     */
    @Override
    public List<RemarkType> queryRemarkTypeList(List<RemarkType> remarkTypeList) {
        Map<Long, List<RemarkType>> childrenMap = remarkTypeList.stream()
                .filter(item -> Objects.equals("0", item.getDisplayStatus()))
                .collect(Collectors.groupingBy(RemarkType::getParentId));
        return getChildren(0L, childrenMap);
    }

    /**
     * 递归查询子节点
     *
     * @param parentId    父id
     * @param childrenMap 子节点Map
     * @return 节点分类列表
     */
    private List<RemarkType> getChildren(Long parentId, Map<Long, List<RemarkType>> childrenMap) {
        return Optional.ofNullable(childrenMap.get(parentId))
                .orElse(Collections.emptyList())
                .stream()
                .peek(item -> item.setChildren(getChildren(item.getRemarkTypeId(), childrenMap)))
                .sorted(Comparator.comparingInt(item -> Optional.ofNullable(item.getSort()).orElse(0)))
                .collect(Collectors.toList());
    }

根据子节点查询所有父节点数据

  /**
     * 根据子节点查询全部父节点
     *
     * @param category 备注类型对象
     * @return 节点集合
     */
    @Override
    public List<String> getParent(RemarkType category) {
        List<String> types = new ArrayList<>();
        //没到顶层节点就一直递归
        if (category.getParentId() != 0L) {
            RemarkType parentCategory = getById(category.getParentId());
            types.addAll(getParent(parentCategory));
        }
        types.add(category.getTypeName());
        return types;
    }