java实现树的组装

java实现树的组装

    
    public List assembleTrees(Collection trees) {
        if (CollectionUtils.isEmpty(trees)) {
            return Collections.emptyList();
        }

        // 构建树主键/实例映射表，并初始化树的子节点集合
        Map mapping = trees.stream().peek(tree -> tree.setChildren(new LinkedList<>()))
                .collect(Collectors.toMap(MeterDeviceVO::getId, t -> t, (o, n) -> n));

        // 查找并关联树节点，返回所有没有父节点的树
        return trees.stream().filter(tree -> {
            MeterDeviceVO parent = ifNull(tree.getParentId(), mapping::get);
            if (parent != null) {
                parent.getChildren().add(tree);
            }
            return Objects.isNull(parent);
        }).collect(Collectors.toList());
    }