SpringBoot整合PageHelper实现分页查询功能

<!-- pageHelper 坐标 -->
<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper-spring-boot-starter</artifactId>
    <version>1.4.6</version>
</dependency>

public class PageBean<T> {
    private Long total;      // 总记录数
    private List<T> items;   // 当前页数据列表
}

//开启分页查询 PageHelp
PageHelper.startPage(pageNum,pageSize);
//直接进入mapper层即可，pagehelper会自动插入LIMIT语句
List<Article>as= articleMapper.list(userid,categoryId,state);

@GetMapping
public Result<PageBean<Article>> list(
    Integer pageNum,
    Integer pageSize,
    @RequestParam(required = false) Integer categoryId,
    @RequestParam(required = false) String state
) {
    PageBean<Article> pb = articleService.list(pageNum, pageSize, categoryId, state);
    return Result.success(pb);
}

@Override
public PageBean<Article> list(Integer pageNum, Integer pageSize, 
                              Integer categoryId, String state) {
    // 1. 创建 PageBean 对象
    PageBean<Article> pb = new PageBean<>();

    // 2. 开启分页查询
    PageHelper.startPage(pageNum, pageSize);

    // 3. 调用 Mapper 查询（此时返回的 List 实际是 Page 类型）
    Map<String, Object> map = ThreadLocalUtil.get();
    Integer userid = (Integer) map.get("id");
    List<Article> as = articleMapper.list(userid, categoryId, state);

    // 4. 强转为 Page 对象，获取分页信息
    Page<Article> p = (Page<Article>) as;

    // 5. 封装结果
    pb.setTotal(p.getTotal());
    pb.setItems(p.getResult());
    return pb;
}

<select id="list" resultType="org.example.pojo.Article">
    select * from article
    <where>
        <if test="categoryId != null">
            category_id = #{categoryId}
        </if>
        <if test="state != null">
            and state = #{state}
        </if>
        and create_user = #{userid}
    </where>
</select>