理论
PageHelper 是基于 Mybatis 提供的一个第三方分页插件，在基于 Mybatis 的项目中使用非常方便。
实践
pom.xml引入依赖
PageHelper 的依赖：
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper-spring-boot-starter</artifactId>
<version>1.2.8</version>
</dependency>
需要引入的其它依赖：
Knife4j 和 Springfox 为 Knife4j 依赖。
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>2.2.2</version>
</dependency>
<dependency>
<groupId>com.github.xiaoymin</groupId>
<artifactId>knife4j-spring-boot-starter</artifactId>
<!--在引用时请在maven中央仓库搜索3.X最新版本号-->
<version>3.0.3</version>
</dependency>
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-boot-starter</artifactId>
<version>3.0.0</version>
</dependency>
application.properties
PageHelper 配置项：
# 分页框架
pagehelper.helperDialect=mysql
pagehelper.reasonable=true
pagehelper.supportMethodsArguments=true
pagehelper.params=count=countSql
需要开启的其它配置项：
# 解决 Springfox 3.X 与 SpringBoot 2.6.X 的版本冲突问题
spring.mvc.pathmatch.matching-strategy=ant_path_matcher
# 开启增强配置
knife4j.enable=true
# 开启Swagger的Basic认证功能,默认是false
knife4j.basic.enable=false
knife4j.basic.username=langjialing
knife4j.basic.password=123456
spring.datasource.username=root
spring.datasource.password=
spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai&useSSL=false
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
mybatis.mapper-locations=classpath:mapper/*.xml
# 开启 mybatis 驼峰映射
mybatis.configuration.map-underscore-to-camel-case=true
Controller层
使用 PageHelper 的注意点：
- 调用静态方法 PageHelper.startPage(pageNo, pageSize) 后只有下一次查询会使用分页，调用过一次查询分页参数自动清除。
- PageHelper.startPage(pageNo, pageSize) 必须放在查询之前，需知道是调用查询时使用到了分页，是属于服务端分页，而不是客户端分页。
package com.langjialing.springbootpagehelperdemo.controller;
import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import com.langjialing.springbootpagehelperdemo.entity.User;
import com.langjialing.springbootpagehelperdemo.service.IUserService;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import java.util.List;
/**
* <p>
* 用户表 前端控制器
* </p>
*
* @author 郎家岭伯爵
* @since 2023-01-11
*/
@Api(tags = "用户操作")
@RestController
@RequestMapping("/user")
public class UserController {
@Autowired
private IUserService userService;
@ApiOperation("查询所有用户")
@GetMapping("/getAllUsers")
public PageInfo<User> getAllUsers(@RequestParam(defaultValue = "1") int pageNo, @RequestParam(defaultValue = "5") int pageSize){
PageHelper.startPage(pageNo, pageSize);
List<User> allUsers = userService.getAllUsers();
return new PageInfo<>(allUsers);
}
}
至此，PageHelper 分页插件的使用在 Controller 层就已经结束了，其它部分代码无变化。但为了保持 DEMO 的完整性，本文接下来会补充其它部分代码。
User实体类
package com.langjialing.springbootpagehelperdemo.entity;
import java.io.Serializable;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.experimental.Accessors;
/**
* <p>
* 用户表
* </p>
*
* @author 郎家岭伯爵
* @since 2023-01-11
*/
@Data
@NoArgsConstructor
@AllArgsConstructor
@Accessors(chain = true)
@ApiModel(value="User对象", description="用户表")
public class User implements Serializable {
private static final long serialVersionUID = 1L;
@ApiModelProperty(value = "用户ID")
private Integer userId;
@ApiModelProperty(value = "用户名")
private String userName;
@ApiModelProperty(value = "用户密码")
private String password;
}
Service层
Service 接口类：
package com.langjialing.springbootpagehelperdemo.service;
import com.langjialing.springbootpagehelperdemo.entity.User;
import java.util.List;
/**
* <p>
* 用户表 服务类
* </p>
*
* @author 郎家岭伯爵
* @since 2023-01-11
*/
public interface IUserService {
/**
* 分页查询用户。
* @return
*/
List<User> getAllUsers();
}
Service 接口实现类：
package com.langjialing.springbootpagehelperdemo.service.impl;
import com.langjialing.springbootpagehelperdemo.entity.User;
import com.langjialing.springbootpagehelperdemo.mapper.UserMapper;
import com.langjialing.springbootpagehelperdemo.service.IUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
/**
* <p>
* 用户表 服务实现类
* </p>
*
* @author 郎家岭伯爵
* @since 2023-01-11
*/
@Service
public class UserServiceImpl implements IUserService {
@Autowired
private UserMapper userMapper;
@Override
public List<User> getAllUsers() {
return userMapper.getAllUsers();
}
}
mapper文件
<?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.langjialing.springbootpagehelperdemo.mapper.UserMapper">
<!-- 通用查询映射结果 -->
<resultMap id="BaseResultMap" type="com.langjialing.springbootpagehelperdemo.entity.User">
<result column="user_name" property="userName" />
<result column="password" property="password" />
</resultMap>
<!-- 通用查询结果列 -->
<sql id="Base_Column_List">
user_id, user_name, password
</sql>
<select id="getAllUsers" resultType="com.langjialing.springbootpagehelperdemo.entity.User">
select <include refid="Base_Column_List"></include>
from `user`
</select>
</mapper>
mapper类
package com.langjialing.springbootpagehelperdemo.mapper;
import com.langjialing.springbootpagehelperdemo.entity.User;
import org.apache.ibatis.annotations.Mapper;
import java.util.List;
/**
* <p>
* 用户表 Mapper 接口
* </p>
*
* @author 郎家岭伯爵
* @since 2023-01-11
*/
@Mapper
public interface UserMapper {
/**
* 分页查询用户。
* @return
*/
List<User> getAllUsers();
}
总结
SpringBoot 整合 PageHelper 插件使用。
