在spring boot项目中使用MyBatis操作数据库

1. 添加MyBatis和MyBatis-Spring依赖

在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.2.0</version>
</dependency>

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.6</version>
</dependency>

2. 配置数据源

在application.properties文件中配置数据源信息，例如：

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/test?serverTimezone=UTC&useSSL=false&characterEncoding=utf8
spring.datasource.username=root
spring.datasource.password=123456

3. 创建实体类和Mapper接口

创建实体类和Mapper接口，例如：

public class User {
    private Long id;
    private String username;
    private String password;
    // 省略getter和setter方法
}

public interface UserMapper {
    User selectById(Long id);
    void insert(User user);
    void update(User user);
    void delete(Long id);
}

4. 编写Mapper.xml文件

在resources目录下创建mapper目录，并创建UserMapper.xml文件，编写SQL语句，例如：

<mapper namespace="com.example.mapper.UserMapper">
    <select id="selectById" parameterType="java.lang.Long" resultType="com.example.entity.User">
        select * from user where id = #{id}
    </select>

    <insert id="insert" parameterType="com.example.entity.User">
        insert into user (username, password) values (#{username}, #{password})
    </insert>

    <update id="update" parameterType="com.example.entity.User">
        update user set username = #{username}, password = #{password} where id = #{id}
    </update>

    <delete id="delete" parameterType="java.lang.Long">
        delete from user where id = #{id}
    </delete>
</mapper>

5. 配置MyBatis

在application.properties文件中添加以下配置：

mybatis.mapper-locations=classpath:mapper/*.xml

6. 注册Mapper接口

在启动类中添加@MapperScan注解，例如：

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

7. 使用Mapper接口操作数据库

在需要使用Mapper接口的地方，通过@Autowired注解注入Mapper接口，并调用其方法，例如：

@RestController
public class UserController {
    @Autowired
    private UserMapper userMapper;

    @GetMapping("/user/{id}")
    public User getUserById(@PathVariable Long id) {
        return userMapper.selectById(id);
    }

    @PostMapping("/user")
    public void addUser(@RequestBody User user) {
        userMapper.insert(user);
    }

    @PutMapping("/user")
    public void updateUser(@RequestBody User user) {
        userMapper.update(user);
    }

    @DeleteMapping("/user/{id}")
    public void deleteUserById(@PathVariable Long id) {
        userMapper.delete(id);
    }
}