使用mybatisplus-join自带的分页方法进行分页查询，不依靠pagehelper,不写xml文件

首先实现类先继承实现好接口：

方法实现，我用的是自带的page方法，把传参pagenum和pagesize放到page对象中，注意这个page对象是导包是从：

package com.baomidou.mybatisplus.extension.plugins.pagination;不能导入错了，ProvinceSorce就是对应数据库的实体类了，用来接受对应的字段；最后这个tableddatainfo是自己封装的返回方法，实际开发中如果不想封装可以直接返回list数据，也就是page.getRecords；

 /**
     * 全身得分情况分页条件查询
     *
     * @param hospitalScoreDetailQuery 筛选条件
     * @return 查询结果
     */
    @Override
        public TableDataInfo queryByPage(HospitalScoreDetailQuery hospitalScoreDetailQuery) {
            if (StringUtils.isBlank(hospitalScoreDetailQuery.getReportDate())){
                return new TableDataInfo(0,Collections.emptyList());
            }
            //获取医院等级字典列表
            List<SysDictData> level = iSysDictTypeService.selectDictDataByType("sys_hosp_leve");
            Map<String, String> collect = level.stream().collect(Collectors.toMap(SysDictData::getDictValue, SysDictData::getDictLabel));
//            PageUtils.startPage();
            MPJLambdaWrapper<ProvinceScore> wrapper= new MPJLambdaWrapper<ProvinceScore>()
                    .selectAll(ProvinceScore.class)
                    .leftJoin(TsWebHospital.class,
                            TsWebHospital::getHospname, ProvinceScore::getHospitalName)
                    .eq(StringUtils.isNotBlank(hospitalScoreDetailQuery.getReportDate()),
                            ProvinceScore::getDate, hospitalScoreDetailQuery.getReportDate())
                    .eq(StringUtils.isNotBlank(hospitalScoreDetailQuery.getHospitalThirdType()), ProvinceScore::getHospitalType,
                            hospitalScoreDetailQuery.getHospitalThirdType())
                    .eq(StringUtils.isNotBlank(hospitalScoreDetailQuery.getLevel()),ProvinceScore::getHospitalLevel,collect.get(hospitalScoreDetailQuery.getLevel()))
                    .orderByAsc(ProvinceScore::getSort);

            //分页核心
            int pageNum = hospitalScoreDetailQuery.getPageNum();
            int pageSize = hospitalScoreDetailQuery.getPageSize();
            //注意导包：mybatisplus
            Page<ProvinceScore> provinceScorePage = new Page<>();
            provinceScorePage.setSize(pageSize);
            provinceScorePage.setCurrent(pageNum);
            provinceScorePage.setOptimizeCountSql(true);
            Page<ProvinceScore> page = page(provinceScorePage, wrapper);
            List<ProvinceScore> records = page.getRecords();
            List<ProvinceScore> provinceScores = Optional.ofNullable(records).orElse(Collections.emptyList());
            List<ProvinceScoreVO> voList = BeanUtil.copyToList(provinceScores, ProvinceScoreVO.class);
            voList.forEach(vo -> {
                //数据封装
                vo.setChapterFive(new ProvinceScoreBO(vo.getChapterFiveTotalScore(), vo.getChapterFiveScore(), vo.getChapterFiveScoreRate()));
                vo.setChapterFour(new ProvinceScoreBO(vo.getChapterFourTotalScore(), vo.getChapterFourScore(), vo.getChapterFourScoreRate()));
                vo.setChapterThree(new ProvinceScoreBO(vo.getChapterThreeTotalScore(), vo.getChapterThreeScore(), vo.getChapterThreeScoreRate()));
                vo.setChapterTwo(new ProvinceScoreBO(vo.getChapterTwoTotalScore(), vo.getChapterTwoScore(), vo.getChapterTwoScoreRate()));
                vo.setChapterOne(new ProvinceScoreBO(vo.getChapterOneTotalScore(), vo.getChapterOneScore(), vo.getChapterOneScoreRate()));
                vo.setQuarterly(new ProvinceScoreBO(vo.getQuarterlyTotalScore(), vo.getQuarterlyScore(), vo.getQuarterlyScoreRate()));
                vo.setYear(new ProvinceScoreBO(vo.getYearTotalScore(), vo.getYearScore(), vo.getYearScoreRate()));
                vo.setHand(new ProvinceScoreBO(vo.getHandTotalScore(), vo.getHandScore(), vo.getHandScoreRate()));
                vo.setAuto(new ProvinceScoreBO(vo.getAutoTotalScore(), vo.getAutoScore(), vo.getAutoScoreRate()));
                vo.setTotal(new ProvinceScoreBO(vo.getTotalScore(), vo.getScore(), vo.getScoreRate()));
                vo.setTotalAchieved(new ProvinceScoreBO(vo.getFullScore(), vo.getTotalAchievedScore(), vo.getTotalAchievedScoreRate()));
            });
            return new TableDataInfo(page.getTotal(), voList);
        }

provinceScorePage.setOptimizeCountSql(true);的作用：在分页的时候会执行两条sql

--原始sql
SELECT * FROM ts_province_score t LEFT JOIN ts_web_hospital t1 ON t1.hospname = t.hospital_name WHERE ...

--开启之后
-- 1. 用来查总数（count）
SELECT COUNT(*) FROM ts_province_score t LEFT JOIN ts_web_hospital t1 ON t1.hospname = t.hospital_name WHERE ...

-- 2. 用来查分页数据
SELECT * FROM ts_province_score t LEFT JOIN ts_web_hospital t1 ON t1.hospname = t.hospital_name WHERE ... LIMIT ? OFFSET ?

附：TableDateInfo返回类，这里的状态码就自己设置了就可以了

import java.io.Serializable;
import java.util.List;

/**
 * 表格分页数据对象
 * 
 * 
 */
public class TableDataInfo implements Serializable
{
    private static final long serialVersionUID = 1L;

    /** 总记录数 */
    private long total;

    /** 列表数据 */
    private List<?> rows;

    /** 消息状态码 */
    private int code;

    /** 消息内容 */
    private String msg;

    /**
     * 表格数据对象
     */
    public TableDataInfo()
    {
    }

    /**
     * 分页
     * 
     * @param list 列表数据
     * @param total 总记录数
     */
    public TableDataInfo(List<?> list, int total)
    {
        this.rows = list;
        this.total = total;
    }
    /**
     * 表格数据对象
     */
    public TableDataInfo(long total, List<?> list)
    {
        this.setCode(HttpStatus.SUCCESS);
        this.setMsg("查询成功");
        this.setTotal(total);
        this.setRows(list);
    }
    public long getTotal()
    {
        return total;
    }

    public void setTotal(long total)
    {
        this.total = total;
    }

    public List<?> getRows()
    {
        return rows;
    }

    public void setRows(List<?> rows)
    {
        this.rows = rows;
    }

    public int getCode()
    {
        return code;
    }

    public void setCode(int code)
    {
        this.code = code;
    }

    public String getMsg()
    {
        return msg;
    }

    public void setMsg(String msg)
    {
        this.msg = msg;
    }
}