问答平台（1），开发社区首页

开发社区首页

- 开发流程
    - 一次请求的执行过程
- 分步实现
    - 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

实体

// DiscussPost.java
public class DiscussPost {

    private int id;

    private int userId;

    private String title;

    private String content;

    private int type;

    private int status;

    private Date createTime;

    private int commentCount;

    private double score;

    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 +
                '}';
    }
}

---

数据访问层

// DiscussPostMapper.java
@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。
    int selectDiscussPostRows(@Param("userId") int userId);
}

<!-- 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.nowcoder.community.dao.DiscussPostMapper">

    <sql id="selectFields">
        id, user_id, title, content, type, status, create_time, comment_count, score
    </sql>

    <sql id="insertFields">
        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>
        <if test="orderMode==0">
            order by type desc, create_time desc
        </if>
        <!-- <if test="orderMode==1">
            order by type desc, score desc, create_time desc
        </if> -->
        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>

---

业务层

// DiscussPostService.java
@Service
public class DiscussPostService {

    @Autowired
    private DiscussPostMapper discussPostMapper;

    public List<DiscussPost> findDiscussPosts(int userId, int offset, int limit) {

        // return discussPostMapper.selectDiscussPosts(userId, offset, limit, orderMode);
        return discussPostMapper.selectDiscussPosts(userId, offset, limit);
    }

    public int findDiscussPostRows(int userId) {
        return discussPostMapper.selectDiscussPostRows(userId);
    }
}

// UserService.java
@Service
public class UserService {

    @Autowired
    private UserMapper userMapper;

    public User findUserById(int id) {
        return userMapper.selectById(id);
    }
}

---

表现层

// HomeController.java
@Controller
public class HomeController {

    @Autowired
    private DiscussPostService discussPostService;

    @Autowired
    private UserService userService;
    
    @RequestMapping(path = "/index", method = RequestMethod.GET)
    public String getIndexPage(Model model, Page page) {
        // 方法调用前，Spring MVC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
        page.setRows(discussPostService.findDiscussPostRows(0));
        page.setPath("/index");

        List<DiscussPost> list = discussPostService
                .findDiscussPosts(0, page.getOffset(), page.getLimit());
        List<Map<String, Object>> discussPosts = new ArrayList<>();
        if (list != null) {
            for (DiscussPost post : list) {
                Map<String, Object> map = new HashMap<>();
                map.put("post", post);
                User user = userService.findUserById(post.getUserId());
                map.put("user", user);
                discussPosts.add(map);
            }
        }
        model.addAttribute("discussPosts", discussPosts);

        return "/index";
    }
}

---

分页

• 实体

  // Page.java
  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 - 1imit
          return (current - 1) * limit;
      }
  
      /**
       * 获取总页数
       *
       * @return
       */
      public int getTotal() {
          // rows / limit
          if (rows % limit == 0) {
              return rows / limit;
          } else {
              return rows / limit + 1;
          }
      }
  
      /**
       * 获取起始页码
       *
       * @return
       */
      public int getFrom() {
          int from = current - 2;
          return (from < 1) ? 1 : from;
      }
  
      /**
       * 获取结束页码
       *
       * @return
       */
      public int getTo() {
          int to = current + 2;
          int total = getTotal();
          return (to > total) ? total : to;
      }
  }

---

页面

• index.html: 调整页面

  <!-- 帖子列表 -->
  <ul class="list-unstyled">
      <li class="media pb-3 pt-3 mb-3 border-bottom" th:each="map:${discussPosts}">
          <a th:href="@{|/user/profile/${map.user.id}|}">
              <img th:src="${map.user.headerUrl}" class="mr-4 rounded-circle" alt="用户头像" style="width:50px;height:50px;">
          </a>
          <div class="media-body">
              <h6 class="mt-0 mb-3">
                  <a th:href="@{|/discuss/detail/${map.post.id}|}" 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="${#dates.format(map.post.createTime, 'yyyy-MM-dd HH:mm:ss')}">2019-04-15 15:32:18</b>
                  <ul class="d-inline float-right">
                      <li class="d-inline ml-2">赞 <span th:text="${map.likeCount}">11</span></li>
                      <li class="d-inline ml-2">|</li>
                      <li class="d-inline ml-2">回帖 <span th:text="${map.post.commentCount}">7</span></li>
                  </ul>
              </div>
          </div>
      </li>
  </ul>
  <!-- 分页 -->
  <nav class="mt-5" th:if="${page.rows>0}" th:fragment="pagination">
      <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" th:href="@{${page.path}(current=${i})}" 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>