在pojo实体类中增加pagebean实体类

@Data
@NoArgsConstructor
@AllArgsConstructor
public class PageBean <T>{
    private Long total;//总条数
    private List<T> items;//当前页数据集合
}

articlecontroller增加代码

@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);
    }

articleserviceimpl增加代码

@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
        PageHelper.startPage(pageNum,pageSize);
        //3.调用mapper
        Map<String,Object> map=ThreadLocalUtil.get();
        Integer userId=(Integer) map.get("id");
        List<Article> as=articleMapper.list(userId,categoryId,state);
        //Page中提供了方法，可以获取PageHelper分页查询后，得到的总记录条数和当前页数据
        Page<Article> p= (Page<Article>) as;
        //把数据填充到PageBean中
        pb.setTotal(p.getTotal());
        pb.setItems(p.getResult());
        return pb;
    }

因为用了 PageHelper.startPage 所以我们要在pom文件中导入依赖

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

实现mapper层方法，我们用动态sql来进行查询

在resource下目录下建立xml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.itheima.mapper.ArticleMapper">

    <!--动态sql-->
    <select id="list" resultType="com.itheima.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>
</mapper>