【java web】论坛实现帖子回复（仿牛客网），帮助大家理清逻辑

一、common表的情况

CREATE TABLE `comment` (`id` int NOT NULL AUTO_INCREMENT,`user_id` int DEFAULT NULL,`entity_type` int DEFAULT NULL,`entity_id` int DEFAULT NULL,`target_id` int DEFAULT NULL,`content` text,`status` int DEFAULT NULL,`create_time` timestamp NULL DEFAULT NULL,PRIMARY KEY (`id`),KEY `index_user_id` (`user_id`) /*!80000 INVISIBLE */,KEY `index_entity_id` (`entity_id`)
) ENGINE=InnoDB AUTO_INCREMENT=232 DEFAULT CHARSET=utf8mb3

entity_type=1时，该实体是一个帖子的评论；
entity_type=2时，该实体是一个帖子中评论的回复；

二、Common Entity

package com.nowcoder.community.entity;import java.util.Date;public class Comment {private int id;private int userId;private int entityType;private int entityId;private int targetId;private String Content;private int status;private Date createTime;public int getId() {return id;}public void setId(int id) {this.id = id;}public int getUserId() {return userId;}public void setUserId(int userId) {this.userId = userId;}public int getEntityType() {return entityType;}public void setEntityType(int entityType) {this.entityType = entityType;}public int getEntityId() {return entityId;}public void setEntityId(int entityId) {this.entityId = entityId;}public int getTargetId() {return targetId;}public void setTargetId(int targetId) {this.targetId = targetId;}public String getContent() {return Content;}public void setContent(String content) {Content = content;}public int getStatus() {return status;}public void setStatus(int status) {this.status = status;}public Date getcreateTime() {return createTime;}public void setcreateTime(Date createTime) {this.createTime = createTime;}@Overridepublic String toString() {return "Comment{" +"id=" + id +", userId=" + userId +", entityType=" + entityType +", entityId=" + entityId +", targetId=" + targetId +", Content='" + Content + '\'' +", status=" + status +", createTime=" + createTime +'}';}
}

三、Common相关的Service

package com.nowcoder.community.service;import com.nowcoder.community.dao.CommentMapper;
import com.nowcoder.community.entity.Comment;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;import java.util.List;@Servicepublic class CommentService {@Autowiredprivate CommentMapper commentMapper;public List<Comment> findCommentsByEntity(int entityType, int entityId, int offset, int limit){return commentMapper.selectCommentsByEntity(entityType,entityId,offset,limit);}public int findCommentCount(int entityType, int entityId){return commentMapper.selectCountByEntity(entityType,entityId);}}

四、CommonMapper：定义数据库的操作

selectCommentsByEntity：从common数据库中选出某帖子的评论(entity_type=1)或回复(entity_type=2);
selectCountByEntity：从common数据库中计算某帖子评论数或某帖子的回复数；

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.nowcoder.community.dao.CommentMapper"><sql id="selectFields">id, user_id, entity_type, entity_id, target_id, content, status, create_time</sql><select id="selectCommentsByEntity" resultType="Comment">select <include refid="selectFields"></include>from commentwhere status = 0and entity_type = #{entityType}and entity_id = #{entityId}order by create_time asclimit #{offset}, #{limit}</select><select id="selectCountByEntity">select count(id)from commentwhere status = 0and entity_type = #{entityType}and entity_id = #{entityId}</select></mapper>

四、Common Controller

每个帖子discussPost都有一个CommentList:

每个评论coomon都有一个commonVo，包含回复信息common、作者信息user、回复信息relpys、回复数量replyCount，其结构为：

每个回复reply都有一个replyVo，包含回复信息reply、作者信息user、回复目标作者信息target，其结构为：

@RequestMapping(path="/detail/{discussPostId}", method = RequestMethod.GET)public String getDiscussPost(@PathVariable("discussPostId") int discussPostId, Model model, Page page){// 帖子信息DiscussPost discussPost = discussPostService.findDiscussPostById(discussPostId);model.addAttribute("post",discussPost);// 帖子作者User user = userService.findUserById(discussPost.getUserId());model.addAttribute("user",user);//评论的分页信息page.setLimit(5); //每页显示5条评论page.setPath("/discuss/detail/"+discussPostId);page.setRows(discussPost.getCommentCount());// 评论：给帖子的回复// 回复：给评论的评论// 评论列表List<Comment> commentList = commentService.findCommentsByEntity(ENTITY_TYPE_POST, discussPost.getId(), page.getOffset(), page.getLimit());// 评论的VO列表// 统一封装要显示的数据List<Map<String,Object>> commentVoList = new ArrayList<>();if(commentList != null){ // 评论列表不为空for(Comment comment: commentList){// 一个评论VOMap<String, Object> commentVo = new HashMap<>();// 评论commentVo.put("comment",comment);// 作者commentVo.put("user", userService.findUserById(comment.getUserId()));// 回复列表List<Comment> replyList = commentService.findCommentsByEntity(ENTITY_TYPE_COMMENT, comment.getId(), 0, Integer.MAX_VALUE);// 回复VO列表List<Map<String,Object>> replyVoList = new ArrayList<>();if(replyList != null){for(Comment reply:replyList){Map<String,Object> replyVo = new HashMap<>();// 回复replyVo.put("reply",reply);// 作者replyVo.put("user", userService.findUserById(reply.getUserId()));// 回复的目标User target = reply.getTargetId() == 0 ? null : userService.findUserById(reply.getUserId());replyVo.put("target",target);replyVoList.add(replyVo);}}commentVo.put("replys", replyVoList);// 评论回复的数量int replyCount = commentService.findCommentCount(ENTITY_TYPE_COMMENT, comment.getId());commentVo.put("replyCount",replyCount);commentVoList.add(commentVo);}}model.addAttribute("comments",commentVoList);return "/site/discuss-detail";}
}