springboot实现分页查询

1.环境介绍：

springboot2.7.4

pagehelper1.4.6

mybatis-plus3.5.1

2.需求分析

　　通过前端传回的分页要求的参数<页码，页数据量>，返回结果

　　实现

{
    "code": 0,
    "message": "操作成功",
    "data": {
        "total": 5,
        "items": [
            {
                "id": 1,
                "title": "背景2",
                "content": "测试,测试2,测试3,测试4......",
                "coverImg": "https://www.bing.com",
                "state": "已发布",
                "categoryId": 2,
                "createUser": 3,
                "createTime": "2024-02-01T14:43:27",
                "updateTime": "2024-02-01T14:43:27"
            },
            {
                。。。}

3.具体实现步骤

构建controller类，接受参数

public Result<PageBean<Article>> list(
            Integer pageNum,Integer pageSize,
            @RequestParam(required = false) Integer categoryId,
            @RequestParam(required = false) String state
    )

可通过@RequestParam指定该参数是否必须

impl中实现

@Override
    public PageBean<Article> list(Integer pageNum, Integer pageSize, Integer categoryId, String state) {
        PageBean<Article> pb = new PageBean<>();//PageBean包含一个total，和一个泛型List
        PageHelper.startPage(pageNum,pageSize);//使用PageHelper实现分页
        Map<String,Object> map = ThreadLocalUtil.get();
        Integer userId = (Integer) map.get("id");//查询用户创建的文章时，从threadLocal中读取用户id
        List<Article> as = articleMapper.list(userId,categoryId,state);
        Page<Article> p = (Page<Article>)as;//将List强制转换为Page子类，以调用Page子类中方法
        pb.setTotal(p.getTotal());
        pb.setItems(p.getResult());
        return pb;
    }

mapper.xml实现

<select id="list" resultType="com.example.springdemo.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>