前言

在使用 Mybatis 时，最头痛的就是写分页了，需要先写一个查询count的select语句，然后再写一个真正分页查询的语句，当查询条件多了之后，会发现真的不想花双倍的时间写 count 和 select，幸好我们有 pagehelper 分页插件，pagehelper 是一个强大实用的 MyBatis 分页插件，可以帮助我们快速的实现MyBatis分页功能，而且pagehelper有个优点是，分页和Mapper.xml完全解耦，并以插件的形式实现，对Mybatis执行的流程进行了强化，这有效的避免了我们需要直接写分页 SQL语句 来实现分页功能。
现在我把自己在项目中实现分页的方法总结如下：

1.导入 Maven 依赖

 <!--分页插件-->
<!--  -->
<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper-spring-boot-starter</artifactId>
    <version>1.3.0</version>
</dependency>
  

2.controller中分页方法

  /**
     　　* @Description: 分页查询
     　   * @Param: waterloggingPreventionDto
     　　* @return com.graphsafe.api.msg.RestMessage(封装的返回值信息)
     　　* @author songwp
     　　* @date 2021/11/2 15:00
     　　*/    @PostMapping(value = "getListForPage", produces = "application/json; charset =UTF-8")
    public RestMessage getListForPage(@ Request Body WaterloggingPreventionDto waterloggingPreventionDto){
        WaterloggingPreventionVo result = new WaterloggingPreventionVo();
        List<WaterloggingPrevention> list = waterloggingPrevention service .getListForPage(waterloggingPreventionDto);
        result.setWaterloggingPreventionList(list);
        if (null != waterloggingPreventionDto.getCount()){
            result.setTotal(waterloggingPreventionDto.getCount().intValue());
        }
        return new RestMessage(result);
    }
  

3.service业务方法的实现

 @Override
    public List<WaterloggingPrevention> getListForPage(WaterloggingPreventionDto waterloggingPreventionDto) {
        List<WaterloggingPrevention> list = new ArrayList<>();
        if (waterloggingPreventionDto.getPage() != null && waterloggingPreventionDto.getLimit() != null){
            PageHelper.startPage(waterloggingPreventionDto.getPage(),waterloggingPreventionDto.getLimit());
            list = waterloggingPreventionMapper.getListForPage(waterloggingPreventionDto);
            PageInfo<WaterloggingPrevention> pageInfo = new PageInfo<>(list);
            waterloggingPreventionDto.setCount(pageInfo.getTotal());
        }else {
            list = waterloggingPreventionMapper.getListForPage(waterloggingPreventionDto);
        }
        return list;
    }
  

4.serviceye业务方法接口

 /**
 * @Description: 
 * @ClassName: WaterloggingPreventionService
 * @Author: songwp
 * @Date: 2021/10/16 13:35
 */public interface WaterloggingPreventionService {
    List<WaterloggingPrevention> getListForPage(WaterloggingPreventionDto waterloggingPreventionDto);
}
  

5.Mapper方法接口

 /**
 * @Description: 
 * @ClassName: WaterloggingPreventionMapper
 * @Author: songwp
 * @Date: 2021/10/16 13:30
 */@Mapper
public interface WaterloggingPreventionMapper {
    List<WaterloggingPrevention> getListForPage(WaterloggingPreventionDto waterloggingPreventionDto);

}

  

6.参数实体类

 /**
 * @author songwp
 * @Description:
 * @date 2021/10/29:47
 */@Data
public class WaterloggingPreventionDto {

    @ApiModelProperty(value = "名称")
     private  String name;

    //分页
    @ApiModelProperty(value = "当前页码")
    private Integer page; //当前页第一页是0

    @ApiModelProperty(value = "每页条数")
    private Integer limit;//每页步长

    @ApiModelProperty(value = "总条数")
    private Long count;//总条数
}
  

7.post数据测试分页展示：

古今成大事者，不唯有超世之才，必有坚韧不拔之志！