使用Java语言如何实现评论回复功能

create table `comment` (
 `id` int(11) not null auto_increment comment '主键id',
 `nickname` varchar(255) default null comment '评论者昵称',
 `avatar` varchar(255) comment '评论头像',
 `content` varchar(255) default null comment '评论的内容',
 `blog_id` int(11) default null comment '评论的博客id',
 primary key (`id`)
 ) comment '评论表';

select * from comment where blog_id=#{blog_id}

create table `comment` (
 `id` int(11) not null auto_increment comment '主键id',
 `nickname` varchar(255) default null comment '评论者昵称',
 `avatar` varchar(255) comment '评论头像',
 `content` varchar(255) default null comment '评论的内容',
 `blog_id` int(11) default null comment '评论的博客id',
 `parent_id` int(11) default '-1' comment '父级评论id',
 primary key (`id`)
 ) comment '评论表';

	private static final long serialVersionUID = 1L;

	@ApiModelProperty(value = "主键id")
	@TableId(value = "id", type = IdType.ASSIGN_ID)
	private Integer id;

	@ApiModelProperty(value = "用户昵称")
	@TableField("nickname")
	private String nickname;

	@ApiModelProperty(value = "头像")
	@TableField("avatar")
	private String avatar;
	
	@ApiModelProperty(value = "评论")
	@TableField("comment")
	private String comment;

	@ApiModelProperty(value = "博客id ")
	@TableField("blog_id")
	private Integer blogId;

	@ApiModelProperty(value = "回复评论id")
	@TableField("parent_id")
	private Integer parentId;

@Data
@NoArgsConstructor
@AllArgsConstructor
@Accessors(chain = true)
@ApiModel(value = "评论模型")
@JsonIgnoreProperties(value = { "handler" })
public class ContentDTO {
	private int id;
 private String nickname;
 private String content;
	private List<ContentDTO> children;
}

 <resultMap id="commentDTOMap" type="com.zukxu.items.comment.entity.ContentDTO">
  <id property="id" column="comment_id"></id>
  <result property="nickname" column="nickname"></result>
  <result property="content" column="content"></result>
 
  <association property="children"
      select="com.zukxu.items.comment.mapper.ContentMapper.selectCommentById" column="{blogId=blog_id,parentId=comment_id}"
      fetchType="lazy">
  </association>
 </resultMap>

 <select id="selectCommentById" resultMap="commentDTOMap">
  SELECT comment_id,nickname,content,blog_id,parent_id FROM blog WHERE blog_id = #{blogId} AND parent_id = #{parentId}
 </select>

 public List<CommentDTO> findParent(List<CommentDTO> comments) {

  for (CommentDTO comment : comments) {

   // 防止checkForComodification(),而建立一个新集合
   ArrayList<CommentDTO> fatherChildren = new ArrayList<>();

   // 递归处理子级的回复，即回复内有回复
   findChildren(comment, fatherChildren);

   // 将递归处理后的集合放回父级的孩子中
   comment.setChildren(fatherChildren);
  }
  return comments;
 }

 public void findChildren(CommentDTO parent, List<CommentDTO> fatherChildren) {

  // 找出直接子级
  List<CommentDTO> comments = parent.getChildren();

  // 遍历直接子级的子级
  for (CommentDTO comment : comments) {

   // 若非空，则还有子级，递归
   if (!comment.getChildren().isEmpty()) {
    findChildren(comment, fatherChildren);
   }

   // 已经到了最底层的嵌套关系，将该回复放入新建立的集合
   fatherChildren.add(comment);

   // 容易忽略的地方：将相对底层的子级放入新建立的集合之后
   // 则表示解除了嵌套关系，对应的其父级的子级应该设为空
   comment.setChildren(new ArrayList<>());
  }
 }
}