springboot 配置 mysql

pom.xml:

<!--    database    -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.32</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.9</version>
        </dependency>
        <!--缺少此jar包，导致@Mapper注解无效-->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>3.0.0</version>
        </dependency>
<!--    database    -->

application.yml配置数据源：

spring:
  datasource:
    url: jdbc:mysql://127.0.0.1:3306/databaseName
    driver-class-name: com.mysql.cj.jdbc.Driver
    username: xxxxxx
    password: xxxxxx

启动类添加包扫描：

@MapperScan(basePackages = "com.example.dao") 
@SpringBootApplication
@EnableCaching
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args); } 
    }

创建mapper类：

这里注意mapper不能重载！！

public interface AppMapper {

    @Select("select * from app")
    App findApp();

    @Select("select version from app")
    Long findVersion();

    @Update("update app set version=${version} where id=${id}")
    void updateApp(int id, long version);

}

在Service层调用：

@Service
public class AppServiceImpl implements AppService {

    @Autowired
    AppMapper am;

    public String version(){
        return String.valueOf(am.findVersion());
    }

}

最后再由controller层调用service层即可