1. springboot项目基本配置

springboot基本pom依赖

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.5.2</version>
</parent>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>
</dependencies>

主启动类，此处在 com.hex下建立

package com.hex;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        SpringApplication.run(MainApplication.class, args);
    }
}

2. mysql准备工作

首先创建一个表，这里使用 mysql5.7 为例

CREATE TABLE `sys_user` (
  `id` BIGINT(20) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `user_name` VARCHAR(64) NOT NULL DEFAULT 'NULL' COMMENT '用户名',
  `nick_name` VARCHAR(64) NOT NULL DEFAULT 'NULL' COMMENT '昵称',
  `password` VARCHAR(64) NOT NULL DEFAULT 'NULL' COMMENT '密码',
  `del_flag` INT(11) DEFAULT '0' COMMENT '删除标志（0代表未删除，1代表已删除）',
  PRIMARY KEY (`id`)
) ENGINE=INNODB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COMMENT='用户表'

引入mysql依赖

<!-- 引入mysql依赖-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

在resources下新建application.yml文件，配置mysql相关信息（按实际自行修改配置）

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/db2022?characterEncoding=utf-8&serverTimezone=UTC
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver

3. 使用mybaitsplus

引入依赖

<!-- 引入mybaitsplus依赖-->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.3</version>
</dependency>

创建user实体类，这里注意2点

1. 在类定义前加注解 @TableName("sys_user")，参数为表名
2. 在主键上添加注解 @TableId

package com.hex.domain;

import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.io.Serializable;
import java.util.Date;

/**
 * 用户表(User)实体类
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
@TableName("sys_user")
public class User implements Serializable {
    private static final long serialVersionUID = -40356785423868312L;
    
    /**
    * 主键
    */
    @TableId
    private Long id;
    /**
    * 用户名
    */
    private String userName;
    /**
    * 昵称
    */
    private String nickName;
    /**
    * 密码
    */
    private String password;
    /**
    * 删除标志（0代表未删除，1代表已删除）
    */
    private Integer delFlag;
}

创建UserMapper类，继承 BaseMapper<T>

package com.hex.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.hex.domain.User;

public interface UserMapper extends BaseMapper<User> {
}

在主启动类添加扫描mapper注解：@MapperScan("com.hex.mapper")，参数为UserMapper的路径

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.hex.mapper")
public class MainApplication {
    public static void main(String[] args) {
        SpringApplication.run(MainApplication.class, args);
    }
}

4. 单元测试看效果

引入junit依赖

<!--单元测试-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
</dependency>

在test/java/com/hex下，建立测试类 MapperTest，

添加 @SpringBootTest，使用 @Autowired（或者@Resource） 注入userMapper，如下

import com.hex.domain.User;
import com.hex.mapper.UserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.List;

@SpringBootTest
public class MapperTest {

    @Autowired
    public UserMapper userMapper;

    @Test
    public void testUserMapper(){
        List<User> users = userMapper.selectList(null);
        System.out.println(users);
    }
}

结果可在控制台查看用户列表信息输出

2022-02-25 12:40:35.849  INFO 13272 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2022-02-25 12:40:38.134  INFO 13272 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
[User(id=1, userName=hex, nickName=hex, password=123456, delFlag=0)]