How easily understandable manner to achieve a tree view?

Traditional use recursion to find out all the top parent, recycling call getChild (), recursive calls getChild () in getChild () in.

This way I do not feel very good understanding of the complexity of detail for the n + n (the number of all children nodes) , the first n number of executions for detecting all parent node, n (the number of the parent node + all children the number of nodes) is determined from the set each time whether there is a child node. If a set is complete tree structure, the number of the parent node number + all children nodes = n, i.e., to calculate the number of n ^ 2 + n, big O notation O (^ n-2) .

I do so, double loop for matching child nodes, another filter out all child nodes collection. code show as below:

@Data
public class CommentTreeRespDto implements Serializable {

    private static final long serialVersionUID = 9098462797193334657L;

    @ApiModelProperty(value = "评论父id，顶级父id为00000-00000-00000-00000")
    private String parentId;

    @ApiModelProperty(value = "当前日志评论的id")
    private String id;

    @ApiModelProperty(value = "评论内容")
    private String content;

    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    private Date createdDate;

    @ApiModelProperty(value = "评论人")
    private String createdBy;

    @ApiModelProperty(value = "当前评论下的子评论")
    private List<CommentTreeRespDto> childCommentList;
}
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    public List<CommentTreeRespDto> getComment(IdBean<String> id) {
        List<CommentTreeRespDto> comment = queryDao.executeForObjectList("selDiaComByDiaId", id);
        comment.forEach(c -> {
            comment.forEach(m -> {
                if (c.getId().equals(m.getParentId())) {
                    if (!CollectionUtils.isEmpty(m.getChildCommentList())) {
                        c.getChildCommentList().add(m);
                    } else {
                        List<CommentTreeRespDto> cs = Lists.newArrayList();
                        cs.add(m);
                        c.setChildCommentList(cs);
                    }
                }
            });
        });

        return comment.stream()
                .filter(e->(!e.getParentId().equals(PARENT_ID)))
                .collect(Collectors.toList());
    }
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In this way I

1. Easy to understand, than the recursive loop characteristic for a double point of it better understood, using the set.
2. Code is simple, with Java8 Stream flow + lambda expressions, Introduction to understand.
3. In the complete tree structure, the same time complexity. Double loop for filtering n ^ 2 + child node n.

Comments are welcome to write what you think. Together we exchange ~

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