Druid的数据源配置：https://www.cnblogs.com/KuroNJQ/p/11171263.html

1.导入依赖

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.0.1</version>
</dependency>

2.我有一个application-dev.yml和一个applicaion.yml

分别是：

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/wrist?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=false
    username: root
    password: 
    driver-class-name: com.mysql.jdbc.Driver
    type: com.alibaba.druid.pool.DruidDataSource
    druid:
      #初始化大小
      initialSize: 5
      #最小值
      minIdle: 5
      #最大值
      maxActive: 20
      #最大等待时间，配置获取连接等待超时，时间单位都是毫秒ms
      maxWait: 60000
      #配置间隔多久才进行一次检测，检测需要关闭的空闲连接
      timeBetweenEvictionRunsMillis: 60000
      #配置一个连接在池中最小生存的时间
      minEvictableIdleTimeMillis: 300000
      validationQuery: SELECT 1 FROM DUAL
      testWhileIdle: true
      testOnBorrow: false
      testOnReturn: false
      poolPreparedStatements: true
      # 配置监控统计拦截的filters，去掉后监控界面sql无法统计，
      #'wall'用于防火墙，SpringBoot中没有log4j，我改成了log4j2
      filters: stat,wall,log4j2
      #最大PSCache连接
      maxPoolPreparedStatementPerConnectionSize: 20
      useGlobalDataSourceStat: true
      # 通过connectProperties属性来打开mergeSql功能；慢SQL记录
      connectionProperties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=500
      # 配置StatFilter
      web-stat-filter:
        #默认为false，设置为true启动
        enabled: true
        url-pattern: "/*"
        exclusions: "*.js,*.gif,*.jpg,*.bmp,*.png,*.css,*.ico,/druid/*"
      #配置StatViewServlet
      stat-view-servlet:
        url-pattern: "/druid/*"
        #允许那些ip
        allow: 127.0.0.1
        login-username: admin
        login-password: 123456
        #禁止那些ip
        deny: 192.168.1.102
        #是否可以重置
        reset-enable: true
        #启用
        enabled: true

mybatis:
  # model的包
  type-aliases-package: ssm.app.model
  configuration:
　　# 开启驼峰uName自动映射到u_name
    map-underscore-to-camel-case: true

# 打印sql
logging:
  level:
    ssm.app.mapper : debug

spring:
  profiles:
    active: dev

3.mybatis已经可以用了，下面是mapper接口

@Mapper
public interface CountryMapper {

    @Select("select * from Country")
    public List<Country> selectAll();

    @Select("select * from Country where id = #{id}")
    public Country selectCountryById(long id);
}

service：

@Service
public class CountryServiceImpl implements CountryService {
    @Autowired
    private CountryMapper countryMapper;

    @Override
    public List<Country> getCountriesFromDb() {
        return countryMapper.selectAll();
    }

    @Override
    public Country getCountryFromDbById(long id) {
        return countryMapper.selectCountryById(id);
    }
}

controller:

@RestController
public class CountryController extends BaseController {
    private final CountryService countryServiceImpl;

    @Autowired
    public BaseController(CountryService countryServiceImpl) {
        this.countryServiceImpl = countryServiceImpl;
    }

    @RequestMapping("/getAllCountries")
    public List<Country> getAllCountries() {
        return countryServiceImpl.getCountriesFromDb();
    }
}

ok！还有就是记得注意yml的层次关系，别写错了，QAQ！