MyBatis的Dao层实现方式

首先开发mapper接口：

public interface UserMapper {
    // 1、 根据用户ID查询用户信息
    public User findUserById(int id) throws Exception;
    // 2、 添加用户
    public void insertUser(User user) throws Exception;
}

之后创建User的映射文件，在config下创建mapper目录然后创建UserMapper.xml

<mapper namespace="com.itheima.mybatis.mapper.UserMapper">
    <!-- 根据用户ID查询用户信息 -->
    <select id="findUserById" parameterType="int" resultType="User">
        SELECT
        * FROM USER WHERE id =#{id}
    </select>
​
    <!-- 添加用户 -->
    <insert id="insertUser" parameterType="com.itheima.mybatis.po.User">
        <selectKey keyProperty="id" resultType="int" order="AFTER">
            SELECT
            LAST_INSERT_ID()
        </selectKey>
​
        INSERT INTO USER
        (username,birthday,sex,address)
        VALUES(#{username},#{birthday},#{sex},#{address})
    </insert>
</mapper>

之后将映射文件加到全局配置文件即可。然后便可以进行测试：

public class UserMapperTest {
    private SqlSessionFactory sqlSessionFactory;
    @Before
    public void setUp() throws Exception {
        // 读取配置文件
        // 全局配置文件的路径
        String resource = "SqlMapConfig.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        // 创建SqlSessionFactory
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }
​
    @Test
    public void testFindUserById() throws Exception {
        // 创建UserMapper对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
​
        // 由mybatis通过sqlsession来创建代理对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.findUserById(1);
        System.out.println(user);
        sqlSession.close();
    }
    @Test
    public void testInsertUser() throws Exception {
        // 创建UserMapper对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 由mybatis通过sqlsession来创建代理对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = new User();
        user.setUsername("东哥hm19");
        user.setAddress("宝盛西里24号楼");
        mapper.insertUser(user);
        System.out.println(user.getId());
        sqlSession.commit();
        sqlSession.close();
    }
}