目录
2.3 创建 Mapper （实现接口——DiscussPostMapper 类）
3.1 创建业务组件 DiscussPostService 类
3.3 访问数据库（在 dao 包下新建一个 UserMapper 接口）
3.5 创建 UserService：根据 UserId 查询到 User
4.2 在 controller 包下新建 HomeController 类
4.4 改进 Controller，支持分页功能（HomeController 类）
1.前期工作
1.1 添加 spring boot项目
1.2 添加配置文件
在 resources 文件下的 application.properties 中添加配置文件
# ThymeleafProperties
spring.thymeleaf.cache=false
# DataSourceProperties
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/community?characterEncoding=utf-8&useSSL=false&serverTimezone=Hongkong
spring.datasource.username=root
spring.datasource.password=123456
spring.datasource.type=com.zaxxer.hikari.HikariDataSource
spring.datasource.hikari.maximum-pool-size=15
spring.datasource.hikari.minimum-idle=5
spring.datasource.hikari.idle-timeout=30000
# MybatisProperties
mybatis.mapper-locations=classpath:mapper/*.xml
mybatis.type-aliases-package=com.example.demo.entity
mybatis.configuration.useGeneratedKeys=true
mybatis.configuration.mapUnderscoreToCamelCase=true
# logger
logging.level.com.nowcoder.community=debug
开发流程：1次请求的执行过程
实现：
- 开发社区首页，显示前10个帖子
- 开发分页组件，分页显示所有的帖子
2.开发 DAO 层（数据访问层）
2.1 连接数据库
2.2 创建实体类
首先开发 DAO（数据访问层），首先需要创建实体类（在 entity 包下创建 DiscussPost 类）进行封装数据
package com.example.demo.entity;
import java.util.Date;
public class DiscussPost {
private int id;
private int userId;
private String title;
private String content;
private int type;
private int status;//帖子状态
private Date createTime;//创建时间
private int commentCount;//评论数量
private double score;//分数
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 String getTitle() {return title;}
public void setTitle(String title) {this.title = title;}
public String getContent() {return content;}
public void setContent(String content) {this.content = content;}
public int getType() {return type;}
public void setType(int type) {this.type = type;}
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;}
public int getCommentCount() {return commentCount;}
public void setCommentCount(int commentCount) {this.commentCount = commentCount;}
public double getScore() {return score;}
public void setScore(double score) {this.score = score;}
@Override
public String toString() {
return "DiscussPost{" +
"id=" + id +
", userId=" + userId +
", title='" + title + '\'' +
", content='" + content + '\'' +
", type=" + type +
", status=" + status +
", createTime=" + createTime +
", commentCount=" + commentCount +
", score=" + score +
'}';
}
}
2.3 创建 Mapper （实现接口——DiscussPostMapper 类）
- 分页查询查到的是多条数据，返回设置为集合（集合中放入帖子对象）
- 分页用 limit 关键字，后面加两个参数：起始行行号（offset）和每一页显示多少行数据（limit）
- @Param注解用于给参数取别名, 如果只有一个参数,并且在<if>里使用,则必须加别名
package com.example.demo.dao;
import com.example.demo.entity.DiscussPost;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import java.util.List;
@Mapper
public interface DiscussPostMapper {
List<DiscussPost> selectDiscussPosts(int userId, int offset, int limit);
// @Param注解用于给参数取别名, 如果只有一个参数,并且在<if>里使用,则必须加别名.
//查询帖子的行数
int selectDiscussPostRows(@Param("userId") int userId);
}2.4 添加配置文件 mapper
要想实现上述方法，需要提供一个配置文件，需要给每一个方法提供需要的 SQL，在 resources 文件中 mapper 目录下创建 discusspost-mapper.xml：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.demo.dao.DiscussPostMapper">
<sql id="selectFields">
id, user_id, title, content, type, status, create_time, comment_count, score
</sql>
<select id="selectDiscussPosts" resultType="DiscussPost">
select <include refid="selectFields"></include>
from discuss_post
where status != 2
<if test="userId!=0">
and user_id = #{userId}
</if>
order by type desc, create_time desc
limit #{offset}, #{limit}
</select>
<select id="selectDiscussPostRows" resultType="int">
select count(id)
from discuss_post
where status != 2
<if test="userId!=0">
and user_id = #{userId}
</if>
</select>
</mapper>到这里 DAO 已经开发完成，进行测试：
package com.example.demo;
import com.example.demo.dao.DiscussPostMapper;
import com.example.demo.entity.DiscussPost;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.List;
@SpringBootTest
public class MapperTests {
//注入 discussPostMapper
@Autowired
private DiscussPostMapper discussPostMapper;
@Test
public void testSelectPosts() {
List<DiscussPost> list = discussPostMapper.selectDiscussPosts(149, 0, 10);
for(DiscussPost post : list) {
System.out.println(post);
}
int rows = discussPostMapper.selectDiscussPostRows(149);
System.out.println(rows);
}
}
3. 开发 Service 层（业务层）
3.1 创建业务组件 DiscussPostService 类
在 service 包下创建业务组件 DiscussPostService 类（业务层会调用数据访问层）：
- 调用 Mapper，注入 DiscussPostMapper
- 声明一个业务方法：查询某一页的方法，返回类型是集合
- 再添加一个查询行数的方法
package com.example.demo.service;
import com.example.demo.dao.DiscussPostMapper;
import com.example.demo.entity.DiscussPost;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class DiscussPostService {
//查询，调用 Mapper，注入 DiscussPostMapper
@Autowired
private DiscussPostMapper discussPostMapper;
//声明一个业务方法：查询某一页的方法，返回类型是集合
public List<DiscussPost> findDiscussPosts(int userId, int offset, int limit) {
return discussPostMapper.selectDiscussPosts(userId, offset, limit);
}
//查询行数的方法
public int findDiscussPostRows(int userId) {
return discussPostMapper.selectDiscussPostRows(userId);
}
}
得到用户名称username：得到数据，针对每一个单独的 DiscussPost 查询 useId ，把查到的 useId 和 DiscussPost 组合在一起返回给页面
需要提供一个业务方法：根据 userId 查询到 user
3.2 创建用户表 User
首先我们看用户表中有哪些属性：
对 User 表进行增删改查，首先要访问实体类（分装表里的数据），在 entity 包下新建 User 类：
package com.example.demo.entity;
import java.util.Date;
public class User {
private int id;
private String username;
private String password;
private String salt;//盐，为了防止用户密码过于简单进行加密
private String email;
private int type;
private int status;
private String activationCode;//激活码
private String headerUrl;//头像访问路径
private Date createTime;//注册时间
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getSalt() {
return salt;
}
public void setSalt(String salt) {
this.salt = salt;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public int getType() {
return type;
}
public void setType(int type) {
this.type = type;
}
public int getStatus() {
return status;
}
public void setStatus(int status) {
this.status = status;
}
public String getActivationCode() {
return activationCode;
}
public void setActivationCode(String activationCode) {
this.activationCode = activationCode;
}
public String getHeaderUrl() {
return headerUrl;
}
public void setHeaderUrl(String headerUrl) {
this.headerUrl = headerUrl;
}
public Date getCreateTime() {
return createTime;
}
public void setCreateTime(Date createTime) {
this.createTime = createTime;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", password='" + password + '\'' +
", salt='" + salt + '\'' +
", email='" + email + '\'' +
", type=" + type +
", status=" + status +
", activationCode='" + activationCode + '\'' +
", headerUrl='" + headerUrl + '\'' +
", createTime=" + createTime +
'}';
}
}3.3 访问数据库（在 dao 包下新建一个 UserMapper 接口）
- 添加注解 @Mapper
- 根据 id 查询
- 根据用户名查询 user
- 根据邮箱查询 user
- 增加用户（参数为 user 包含的所有数据）
- 修改用户状态（返回修改条数）
- 更新头像路径
- 更新密码
package com.example.demo.dao;
import org.apache.catalina.User;
import org.apache.ibatis.annotations.Mapper;
@Mapper
public interface UserMapper {
//根据 id 查询
User selectById(int id);
//根据用户名查询 user
User selectByName(String username);
//根据邮箱查询 user
User selectByEmail(String email);
//增加用户（参数为 user 包含的所有数据）
int insertUser(User user);
//修改用户状态（返回修改条数
int updateStatus(int id, int status);
//更新头像路径
int updateHeader(int id, String headerUrl);
//更新密码
int updatePassword(int id, String password);
}3.4 配置文件：给每一个方法提供需要的 SQL
要想实现上述方法，需要提供一个配置文件，需要给每一个方法提供需要的 SQL，在 resources 文件中 mapper 目录下创建一个 user-mapper 的配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.demo.dao.UserMapper">
<sql id="insertFields">
username, password, salt, email, type, status, activation_code, header_url, create_time
</sql>
<sql id="selectFields">
id, username, password, salt, email, type, status, activation_code, header_url, create_time
</sql>
<select id="selectById" resultType="User">
select <include refid="selectFields"></include>
from user
where id = #{id}
</select>
<select id="selectByName" resultType="User">
select <include refid="selectFields"></include>
from user
where username = #{username}
</select>
<select id="selectByEmail" resultType="User">
select <include refid="selectFields"></include>
from user
where email = #{email}
</select>
<insert id="insertUser" parameterType="User" keyProperty="id">
insert into user (<include refid="insertFields"></include>)
values(#{username}, #{password}, #{salt}, #{email}, #{type}, #{status}, #{activationCode}, #{headerUrl}, #{createTime})
</insert>
<update id="updateStatus">
update user set status = #{status} where id = #{id}
</update>
<update id="updateHeader">
update user set header_url = #{headerUrl} where id = #{id}
</update>
<update id="updatePassword">
update user set password = #{password} where id = #{id}
</update>
</mapper>3.5 创建 UserService：根据 UserId 查询到 User
在 service 包下创建 UserService 类：
- 添加注解 @Service
- 查询用户：需要注入用户的 Mapper（UserMapper）
package com.example.demo.service;
import com.example.demo.dao.UserMapper;
import org.apache.catalina.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
/**
* 根据 UserId 查询到 User
*/
@Service
public class UserService {
@Autowired
private UserMapper userMapper;
//根据一个用户 id 查询用户的方法
public User findUserById(int id) {
return userMapper.selectById(id);
}
}
4.开发 Controller 层
4.1 首先引入前端页面
<!doctype html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<link rel="icon" href="https://static.nowcoder.com/images/logo_87_87.png"/>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" crossorigin="anonymous">
<link rel="stylesheet" th:href="@{/css/global.css}" />
<title>牛客网-首页</title>
</head>
<body>
<div class="nk-container">
<!-- 头部 -->
<header class="bg-dark sticky-top">
<div class="container">
<!-- 导航 -->
<nav class="navbar navbar-expand-lg navbar-dark">
<!-- logo -->
<a class="navbar-brand" href="#"></a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<!-- 功能 -->
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav mr-auto">
<li class="nav-item ml-3 btn-group-vertical">
<a class="nav-link" href="index.html">首页</a>
</li>
<li class="nav-item ml-3 btn-group-vertical">
<a class="nav-link position-relative" href="site/letter.html">消息<span class="badge badge-danger">12</span></a>
</li>
<li class="nav-item ml-3 btn-group-vertical">
<a class="nav-link" href="site/register.html">注册</a>
</li>
<li class="nav-item ml-3 btn-group-vertical">
<a class="nav-link" href="site/login.html">登录</a>
</li>
<li class="nav-item ml-3 btn-group-vertical dropdown">
<a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
<img src="http://images.nowcoder.com/head/1t.png" class="rounded-circle" style="width:30px;"/>
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item text-center" href="site/profile.html">个人主页</a>
<a class="dropdown-item text-center" href="site/setting.html">账号设置</a>
<a class="dropdown-item text-center" href="site/login.html">退出登录</a>
<div class="dropdown-divider"></div>
<span class="dropdown-item text-center text-secondary">nowcoder</span>
</div>
</li>
</ul>
<!-- 搜索 -->
<form class="form-inline my-2 my-lg-0" action="site/search.html">
<input class="form-control mr-sm-2" type="search" aria-label="Search" />
<button class="btn btn-outline-light my-2 my-sm-0" type="submit">搜索</button>
</form>
</div>
</nav>
</div>
</header>
<!-- 内容 -->
<div class="main">
<div class="container">
<div class="position-relative">
<!-- 筛选条件 -->
<ul class="nav nav-tabs mb-3">
<li class="nav-item">
<a class="nav-link active" href="#">最新</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">最热</a>
</li>
</ul>
<button type="button" class="btn btn-primary btn-sm position-absolute rt-0" data-toggle="modal" data-target="#publishModal">我要发布</button>
</div>
<!-- 弹出框 -->
<div class="modal fade" id="publishModal" tabindex="-1" role="dialog" aria-labelledby="publishModalLabel" aria-hidden="true">
<div class="modal-dialog modal-lg" role="document">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="publishModalLabel">新帖发布</h5>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">×</span>
</button>
</div>
<div class="modal-body">
<form>
<div class="form-group">
<label for="recipient-name" class="col-form-label">标题：</label>
<input type="text" class="form-control" id="recipient-name">
</div>
<div class="form-group">
<label for="message-text" class="col-form-label">正文：</label>
<textarea class="form-control" id="message-text" rows="15"></textarea>
</div>
</form>
</div>
<div class="modal-footer">
<button type="button" class="btn btn-secondary" data-dismiss="modal">取消</button>
<button type="button" class="btn btn-primary" id="publishBtn">发布</button>
</div>
</div>
</div>
</div>
<!-- 提示框 -->
<div class="modal fade" id="hintModal" tabindex="-1" role="dialog" aria-labelledby="hintModalLabel" aria-hidden="true">
<div class="modal-dialog modal-lg" role="document">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="hintModalLabel">提示</h5>
</div>
<div class="modal-body" id="hintBody">
发布完毕!
</div>
</div>
</div>
</div>
<!-- 帖子列表 -->
<ul class="list-unstyled">
<li class="media pb-3 pt-3 mb-3 border-bottom" th:each="map:${discussPosts}">
<a href="site/profile.html">
<img th:src="${map.user.headerUrl}" class="mr-4 rounded-circle" alt="用户头像" style="width:50px;height:50px;">
</a>
<div class="media-body">
<h6 class="mt-0 mb-3">
<a href="#" th:utext="${map.post.title}">备战春招，面试刷题跟他复习，一个月全搞定！</a>
<span class="badge badge-secondary bg-primary" th:if="${map.post.type==1}">置顶</span>
<span class="badge badge-secondary bg-danger" th:if="${map.post.status==1}">精华</span>
</h6>
<div class="text-muted font-size-12">
<u class="mr-3" th:utext="${map.user.username}">寒江雪</u> 发布于 <b th:text="${#dates.format(map.post.createTime,'yyyy-MM-dd HH:mm:ss')}">2019-04-15 15:32:18</b>
<ul class="d-inline float-right">
<li class="d-inline ml-2">赞 11</li>
<li class="d-inline ml-2">|</li>
<li class="d-inline ml-2">回帖 7</li>
</ul>
</div>
</div>
</li>
</ul>
<!-- 分页 -->
<nav class="mt-5" th:if="${page.rows>0}">
<ul class="pagination justify-content-center">
<li class="page-item">
<a class="page-link" th:href="@{${page.path}(current=1)}">首页</a>
</li>
<li th:class="|page-item ${page.current==1?'disabled':''}|">
<a class="page-link" th:href="@{${page.path}(current=${page.current-1})}">上一页</a></li>
<li th:class="|page-item ${i==page.current?'active':''}|" th:each="i:${#numbers.sequence(page.from,page.to)}">
<a class="page-link" href="#" th:text="${i}">1</a>
</li>
<li th:class="|page-item ${page.current==page.total?'disabled':''}|">
<a class="page-link" th:href="@{${page.path}(current=${page.current+1})}">下一页</a>
</li>
<li class="page-item">
<a class="page-link" th:href="@{${page.path}(current=${page.total})}">末页</a>
</li>
</ul>
</nav>
</div>
</div>
<!-- 尾部 -->
<footer class="bg-dark">
<div class="container">
<div class="row">
<!-- 二维码 -->
<div class="col-4 qrcode">
<img src="https://uploadfiles.nowcoder.com/app/app_download.png" class="img-thumbnail" style="width:136px;" />
</div>
<!-- 公司信息 -->
<div class="col-8 detail-info">
<div class="row">
<div class="col">
<ul class="nav">
<li class="nav-item">
<a class="nav-link text-light" href="#">关于我们</a>
</li>
<li class="nav-item">
<a class="nav-link text-light" href="#">加入我们</a>
</li>
<li class="nav-item">
<a class="nav-link text-light" href="#">意见反馈</a>
</li>
<li class="nav-item">
<a class="nav-link text-light" href="#">企业服务</a>
</li>
<li class="nav-item">
<a class="nav-link text-light" href="#">联系我们</a>
</li>
<li class="nav-item">
<a class="nav-link text-light" href="#">免责声明</a>
</li>
<li class="nav-item">
<a class="nav-link text-light" href="#">友情链接</a>
</li>
</ul>
</div>
</div>
<div class="row">
<div class="col">
<ul class="nav btn-group-vertical company-info">
<li class="nav-item text-white-50">
公司地址：北京市朝阳区大屯路东金泉时代3-2708北京牛客科技有限公司
</li>
<li class="nav-item text-white-50">
联系方式：010-60728802(电话) admin@nowcoder.com
</li>
<li class="nav-item text-white-50">
牛客科技©2018 All rights reserved
</li>
<li class="nav-item text-white-50">
京ICP备14055008号-4
<img src="http://static.nowcoder.com/company/images/res/ghs.png" style="width:18px;" />
京公网安备 11010502036488号
</li>
</ul>
</div>
</div>
</div>
</div>
</div>
</footer>
</div>
<script src="https://code.jquery.com/jquery-3.3.1.min.js" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" crossorigin="anonymous"></script>
<script th:src="@{/js/global.js}"></script>
<script th:src="@{js/index.js}"></script>
</body>
</html>4.2 在 controller 包下新建 HomeController 类
- 省略 Controller 的访问路径，直接访问方法即可
- 在查询的时候调用 Service，因此注入 DiscussPostService
- 注入 UserService：通过 discussPostService 查询到数据中的只是 userId，通过 UserService 把 user的详细数据查询到
package com.example.demo.controller;
import com.example.demo.entity.DiscussPost;
import com.example.demo.service.DiscussPostService;
import com.example.demo.service.UserService;
import org.apache.catalina.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
@Controller
public class HomeController {
//在查询的时候调用 Service，因此注入 DiscussPostService
@Autowired
private DiscussPostService discussPostService;
//通过 discussPostService 查询到数据中的只是 userId，通过 UserService 把 user的详细数据查询到
@Autowired
private UserService userService;
@RequestMapping(path = "/index", method = RequestMethod.GET)//访问首页路径
public String getIndexPage(Model model) {
//只是查询到 userId，不是用户名，但是我们需要展示用户名
List<DiscussPost> list = discussPostService.findDiscussPosts(0,0,10);
//遍历集合，针对每一个 DiscussPost 的 userId 查询到 user，再把数据组装放到新的集合返回给页面
//新建集合，能够封装 DiscussPost 和 User 对象
List<Map<String, Object>> discussPosts = new ArrayList<>();
if(list != null) {
for (DiscussPost post : list) {
Map<String, Object> map = new HashMap<>();//最终结果放到 Map 中，实例化 Map
map.put("post", post);
User user = userService.findUserById(post.getUserId());//得到 user 的完整数据
map.put("user", user);
discussPosts.add(map);
}
}
model.addAttribute("discussPosts", discussPosts);
return "/index";//返回模板路径
}
}
4.3 封装分页相关的信息
在 entity 包下新建 Page类：
package com.example.demo.entity;
/**
* 封装分页相关的信息.
*/
public class Page {
// 当前页码
private int current = 1;
// 显示上限
private int limit = 10;
// 数据总数(用于计算总页数)
private int rows;
// 查询路径(用于复用分页链接)
private String path;
public int getCurrent() {
return current;
}
public void setCurrent(int current) {
if (current >= 1) {
this.current = current;
}
}
public int getLimit() {
return limit;
}
public void setLimit(int limit) {
if (limit >= 1 && limit <= 100) {
this.limit = limit;
}
}
public int getRows() {
return rows;
}
public void setRows(int rows) {
if (rows >= 0) {
this.rows = rows;
}
}
public String getPath() {
return path;
}
public void setPath(String path) {
this.path = path;
}
/**
* 获取当前页的起始行
*
* @return
*/
public int getOffset() {
// current * limit - limit
return (current - 1) * limit;
}
/**
* 获取总页数
*
* @return
*/
public int getTotal() {
// rows / limit [+1]
if (rows % limit == 0) {
return rows / limit;
} else {
return rows / limit + 1;
}
}
/**
* 获取起始页码：最近的两页
*
* @return
*/
public int getFrom() {
int from = current - 2;
return from < 1 ? 1 : from;
}
/**
* 获取结束页码：同样也是两页
*
* @return
*/
public int getTo() {
int to = current + 2;
int total = getTotal();
return to > total ? total : to;
}
}4.4 改进 Controller，支持分页功能（HomeController 类）
- 分页会传入分页的条件，使用 Page 进行分装
- 设置分页总行数、分页访问路径
- 这时候查询帖子的时候就可以动态的写入：获取当前页的起始行——page.getOffset(), 总页码—— page.getLimit()
- 方法调用之前, SpringMVC 会自动实例化 Model 和 Page ,并将 Page 注入 Model，所以,在 thymeleaf 中可以直接访问 Page 对象中的数据.
package com.example.demo.controller;
import com.example.demo.entity.DiscussPost;
import com.example.demo.entity.Page;
import com.example.demo.entity.User;
import com.example.demo.service.DiscussPostService;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
@Controller
public class HomeController {
//在查询的时候调用 Service，因此注入 DiscussPostService
@Autowired
private DiscussPostService discussPostService;
//通过 discussPostService 查询到数据中的只是 userId，通过 UserService 把 user的详细数据查询到
@Autowired
private UserService userService;
@RequestMapping(path = "/index", method = RequestMethod.GET)//访问首页路径
public String getIndexPage(Model model, Page page) {
// 方法调用之前,SpringMVC会自动实例化Model和Page,并将Page注入Model.
// 所以,在thymeleaf中可以直接访问Page对象中的数据.
//加入分页功能
page.setRows(discussPostService.findDiscussPostRows(0));//设置总行数
page.setPath("/index");//访问路径
//只是查询到 userId，不是用户名，但是我们需要展示用户名
List<DiscussPost> list = discussPostService.findDiscussPosts(0, page.getOffset(), page.getLimit());
//遍历集合，针对每一个 DiscussPost 的 userId 查询到 user，再把数据组装放到新的集合返回给页面
//新建集合，能够封装 DiscussPost 和 User 对象
List<Map<String, Object>> discussPosts = new ArrayList<>();
if (list != null) {
for (DiscussPost post : list) {
Map<String, Object> map = new HashMap<>();//最终结果放到 Map 中，实例化 Map
map.put("post", post);
User user = userService.findUserById(post.getUserId());//得到 user 的完整数据
map.put("user", user);
discussPosts.add(map);
}
}
model.addAttribute("discussPosts", discussPosts);
return "/index";//返回模板路径
}
}
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