1.2.2、第二种：利用注解的形式整合

1、SQL

1.1、数据库连接

导入依赖

<!--导入jdbc场景-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jdbc</artifactId>
</dependency>

<!--数据库驱动-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

修改配置项

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mybatis_plus
    username: root
    password: 1017
    driver-class-name: com.mysql.cj.jdbc.Driver

测试

@Slf4j
@SpringBootTest
class Springboot2WebApplicationTests {

    @Autowired
    JdbcTemplate jdbcTemplate;

    @Test
    void contextLoads() {
        Long aLong = jdbcTemplate.queryForObject("select count(*) from user", Long.class);
        log.info("记录总数：{}",aLong);
    }
}

1.2、整合MyBatis操作

1.2.1、第一种：利用配置文件的形式整合

导入mybatis依赖

<!--mybatis-->
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.1.4</version>
</dependency>

工程的目录结构如下

编写实体类User

@Data
public class User {

    private Integer id;
    private String name;
    private Integer age;
    private String email;
}

编写mapper接口层，标准@Mapper注解

@Mapper
public interface UserMapper {

    /**
     * @Description：根据id查询员工信息
     * @Author：crz
     * @Date：2022/2/12 13:33
     */
    public User getUse(Integer id);
}

编写sql映射文件并绑定mapper接口

<?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.crz.springboot.mapper.UserMapper">

    <!-- 根据id查询员工信息 -->
    <!--public User getUse(Integer id);-->
    <select id="getUse" resultType="com.crz.springboot.bean.User">
        SELECT * FROM user WHERE id=#{id}
    </select>
</mapper>

在 application.yml 中进行相关配置

mybatis:
  # 全局配置文件的位置
  #config-location: classpath:mybatis/mybatis-config.xml
  # mapper sql映射文件的位置
  mapper-locations: classpath:mybatis/mapper/*.xml
  configuration:
    map-underscore-to-camel-case: true #开启驼峰命名法

#可以不写全局；配置文件，所有全局配置文件的配置都放在configuration配置项中即可

编写 Service 层

@Service
public class UserService {

    @Autowired
    UserMapper userMapper;

    public User getUserId(Integer id){
        return userMapper.getUse(id);
    }
}

编写 Controller 层

@Controller
public class UserController {

    @Autowired
    UserService userService;

    @ResponseBody
    @GetMapping("/user")
    public User getUser(@RequestParam("id") Integer id){
        return userService.getUserId(id);
    }
}

测试

1.2.2、第二种：利用注解的形式整合

工程的目录结构如下

编写实体类City

@Data
public class City {

    private Integer id;
    private String name;
    private Integer age;
    private String email;
}

编写mapper接口层，标准@Mapper注解

@Mapper
public interface CityMapper {

    @Select("select * from city where id=#{id}")
    public City getById(Integer id);
}

编写 Service 层

@Service
public class CityService {

    @Autowired
    CityMapper cityMapper;

    public City getById(Integer id){
        return cityMapper.getById(id);
    }
}

编写 Controller 层

@Controller
public class CityController {

    @Autowired
    CityService cityService;

    @ResponseBody
    @GetMapping("/city")
    public City getCityById(@RequestParam("id") Integer id){
        return cityService.getById(id);
    }
}

测试

1.3、整合 MyBatis-Plus 操作

导入mybatis-plus依赖

<!--mybatis-plus-->        
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.1</version>
</dependency>

编写实体类User

@Data
public class User {

    private Integer id;
    private String name;
    private Integer age;
    private String email;
}

编写mapper接口层，标准@Mapper注解

@Mapper
public interface UserMapper extends BaseMapper<User> {

}

在com/crz/springboot/Springboot2WebApplicationTests.java文件进行测试

@Autowired
    UserMapper userMapper;

    @Test
    void testUserMapper(){
        User user = userMapper.selectById(1L);
        System.out.println("用户信息："+user);
    }

测试