springboot如何集成mybatis中的分页插件pagehelper

为什么要引入pagehelper（这里代码简写）

原始写法计算起始页 (page-1)*pageSize,pageSize

结束页 pageSize

select 字段名称.....  from 表名 limit 起始页，结束页

 有个这个以后就不用这么写了直接使用下面的方法即可。

（1）导入pom.xml依赖

	<!--父级项目依赖-->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.5.RELEASE</version>
	</parent>
	<properties>
		<java.version>1.8</java.version>
		<fastjson_version>1.2.28</fastjson_version>
		<!--mybatis-->
		<mybatis-spring-boot-starter>2.0.0</mybatis-spring-boot-starter>
		<!--alibaba数据源-->
		<alibaba>1.0.29</alibaba>
		<!--mysql-->
		<mysql>5.1.47</mysql>
<pagehelper>1.2.5</pagehelper>
	</properties>
<dependencies>
<dependency>
			<groupId>com.github.pagehelper</groupId>
			<artifactId>pagehelper-spring-boot-starter</artifactId>
			<version>${pagehelper}</version>
		</dependency>
<!--web支持的jar springboot的启动器-->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	<!--数据库驱动-->
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>${mysql}</version>
		</dependency>
<dependency>
			<groupId>com.alibaba</groupId>
			<artifactId>druid</artifactId>
			<version>${alibaba}</version>
		</dependency>
	<dependency>
			<groupId>org.mybatis.spring.boot</groupId>
			<artifactId>mybatis-spring-boot-starter</artifactId>
			<version>${mybatis-spring-boot-starter}</version>
		</dependency>
</dependencies>

（2）编写配置文件application.yml

#  指定端口
spring:
server:
  port: 8999
# 分页配置
pagehelper:
  helper-dialect: mysql
  reasonable: true
  support-methods-arguments: true
  params: count=countSql
#mysql连接
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.jdbc.Driver
    username: root
    password: root
    url: jdbc:mysql://localhost:3306/ems?serverTimezone=UTC&useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&useSSL=false
mybatis:
  type-aliases-package: springsecurity.entity
  mapper-locations: classpath:com/baidu/mapper/*.xml

(2)编写实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class log {
    private Integer id;
    private String username;
    @JsonFormat(pattern = "yyyy-MM-dd")
    private Date date;
    private String operation;
}

(3)编写dao mapper层

@Mapper
public interface logDao(){
 List<log> queryAll();
}

(4)编写dao的实现logDaoImpl.xml

<?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="springsecurity.Dao.logMapper">
    <insert id="add" useGeneratedKeys="true" parameterType="log">
        insert into log value(#{id},#{username},#{date},#{operation})
    </insert>
    <select id="queryAll" resultType="springsecurity.entity.log">
        select * from log
    </select>

</mapper>

(5)编写server

public interface logService {
    PageInfo<log> listUser(int currentPage, int pageSize);
}

(6)编写serverImpl

@Service
@Transactional
public class logServeImpl implements logService{
    @Autowired
    private logMapper logMapper;
    @Override
    public PageInfo<log> listUser(int pageNum, int pageSize) {
        PageHelper.startPage(pageNum,pageSize);
        // 查询数据库
        List<log> userDOList = logMapper.queryAll();
        // UserDO->UserVO...
        PageInfo pageInfo = new PageInfo(userDOList);
        return pageInfo;
    }
}

(7)编写controller

@RestController
@RequestMapping(value = "log")
public class logController {


private logService logService;
@Autowired
    public logController(springsecurity.service.serviceImpl.logService logService) {
        this.logService = logService;
    }
/**
参数说明
page 当前页数
pageSize 一页展示几条
**/
    @GetMapping(value = "/logs")
    public List<log> queryList(@RequestParam(value = "page",required = false,defaultValue ="1") int page,@RequestParam(value = "pageSize",required = false,defaultValue = "3") int pageSize){
         final PageInfo<log> logPageInfo = logService.listUser(page, pageSize);
         final int nextPage=logPageInfo.getNextPage();
         logPageInfo.getTotal();
         System.out.println("查询出来的条数"+nextPage);
         System.out.println("总条数"+total);
        return logPageInfo.getList();
    }
}

(8)测试 http://localhost:8999/log/logs