PageHelper can also be combined with lambda expressions to achieve concise paging encapsulation

1、 introduce POM

        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.4.2</version>
        </dependency>

2、 encapsulation PageBean

Create query paging class BaseQueryParam, The query parameter class it needs to pass , You can inherit directly , The code is as follows ：

@Data
public class BaseQueryParam {
    
    /** *  The current page number  */
    private Integer pageNum;

    /** *  Number of pages  */
    private Integer pageSize;
}

Encapsulate the new PageBean, Use generics to encapsulate unified request method and response paging information parameters , The code is as follows ：

import com.github.pagehelper.ISelect;
import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import java.util.List;

public class NewPageBean<T> {
    
    private Long total;
    private List<T> list;
    private MyPage pageInfo;

    /** * @param select  call Mapper The result of the interface  * @param param  Request parameters  * @param tClass  Responsive Class object  * @param <T> * @return */
    public static <T> NewPageBean<T> generatePage(ISelect select, BaseQueryParam param, Class<T> tClass) {
    
        Integer current = param.getPageNum();
        Integer pageSize = param.getPageSize();
        List<T> list = PageHelper
                .startPage(current == null ? 1 : current, pageSize == null ? 10 : pageSize)
                .doSelectPage(select);
        return new NewPageBean<>(list);
    }

    public NewPageBean(List<T> list) {
    
        PageInfo<T> pageInfo = new PageInfo<>(list);
        this.total = pageInfo.getTotal();
        this.list = list;
        MyPage page = new MyPage();
        page.setTotalPage(pageInfo.getPages());
        page.setPageNum(pageInfo.getPageNum());
        page.setPageSize(pageInfo.getPageSize());
        page.setPreviousPage(pageInfo.getPrePage());
        page.setNextPage(pageInfo.getNextPage());
        this.pageInfo = page;
    }

    public long getNum() {
    
        return this.total;
    }

    public void setNum(Long total) {
    
        this.total = total;
    }

    public Long getTotal() {
    
        return total;
    }

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

    public List<T> getList() {
    
        return list;
    }

    public void setList(List<T> list) {
    
        this.list = list;
    }

    public MyPage getPageInfo() {
    
        return pageInfo;
    }

    public void setPageInfo(MyPage pageInfo) {
    
        this.pageInfo = pageInfo;
    }

    static class MyPage {
    
        private int pageNum;
        private int pageSize;
        private int totalPage;
        private int nextPage;
        private int previousPage;

        public int getPageNum() {
    
            return pageNum;
        }

        public void setPageNum(int pageNum) {
    
            this.pageNum = pageNum;
        }

        public int getPageSize() {
    
            return pageSize;
        }

        public void setPageSize(int pageSize) {
    
            this.pageSize = pageSize;
        }

        public int getTotalPage() {
    
            return totalPage;
        }

        public void setTotalPage(int totalPage) {
    
            this.totalPage = totalPage;
        }

        public int getNextPage() {
    
            return nextPage;
        }

        public void setNextPage(int nextPage) {
    
            this.nextPage = nextPage;
        }

        public int getPreviousPage() {
    
            return previousPage;
        }

        public void setPreviousPage(int previousPage) {
    
            this.previousPage = previousPage;
        }
    }
}

3、 usage

3.1 Definition Mapper

@Mapper
public interface TaskMapper {
    
	List<Task> list(BaseQueryParam param);
}

3.2 Definition Mapping

<?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.mapper.TaskMapper">

    <select id="list" parameterType="com.lhz.controller.page.BaseQueryParam" resultMap="BaseResultMap">
        select
            id,name,create_by,create_time,update_by,update_time,remark
        from sys_task
    </select>
    
</mapper>

3.3 Concrete realization

Don't write here servce, layer , Convenient demonstration directly in Controller Call in Mapper

@RestController	
public class TaskController {
    

    @Resource
    private TaskMapper taskMapper;

    @GetMapping("test")
    public Object test(BaseQueryParam param) {
    
        /** * BaseQueryParam  Is the query parameter  * Task  Is the entity that responded  */
        return NewPageBean.generatePage(() -> taskMapper.list(param), param, Task.class);
    }
}

4、 test

test url：http://localhost:9090/demo/test?pageNum=2&pageSize=2

SQL preview ：

Return results ：

{
    
    "total":3,
    "list":[
        {
    
            "id":"1",
            "name":" Timed task one ",
            "createBy":"1",
            "createTime":1601178428000,
            "updateBy":"1",
            "updateTime":1601178428000,
            "remark":""
        },
        {
    
            "id":"2",
            "name":" Timed task two ",
            "createBy":"1",
            "createTime":1601178546000,
            "updateBy":"1",
            "updateTime":1601178546000,
            "remark":""
        }
    ],
    "pageInfo":{
    
        "pageNum":1,
        "pageSize":2,
        "totalPage":2,
        "nextPage":2,
        "previousPage":0
    },
    "num":3
}