Mybatis的Dao为什么都是接口

我们在使用mybatis做orm时, 只需要告知框架我们的mapper映射和domian所在位置即可, 不需要实现类, mybatis是如何帮我们访问数据库的呢 ?

debug查看dao接口的mybatis的实现类

// 追踪代码每个接口的实现类是MapperProxy
// 该类实现了 `InvocationHandler` 使用的jdk的动态代理
public class MapperProxy<T> implements InvocationHandler, Serializable {
}

我们自己来实现一个简单的mybatis

1. 创建接口
2. 创建代理类
3. 向mvc中注入代理类
4. 测试调用

创建接口类

public interface UserDao {
    public User getById(String id);
}

创建代理类

public class IBatisProxy implements InvocationHandler
{
    private HikariDataSource pool;

    public IBatisProxy(HikariDataSource pool)
    {
        this.pool = pool;
    }

    @ Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
    {
        Connection connection = pool.getConnection();
        PreparedStatement statement = connection.prepareStatement("select * from dem_user where id =?");
        statement.setString(1, args[0].toString());
        ResultSet resultSet = statement.executeQuery();

        resultSet.next();
        String id = resultSet.getString("id");
        String name = resultSet.getString("name");
        String account = resultSet.getString("account");
        String password = resultSet.getString("password");
        String auth = resultSet.getString("auth");
        String organId = resultSet.getString("organ_id");
        User user = new User(id, name, account, password, auth, organId);

        connection.close();
        return user;
    }

}

向ApplicationContext中注入代理类

@ Configuration
public class UserDaoConfig
{

    @ Autowired
    private HikariDataSource hikariDataSource;

    @ Bean
    public UserDao userDao2()
    {
        Class<UserDao> clazz = UserDao.class;
        UserDao userDao = (UserDao)Proxy.newProxyInstance(clazz.getClassLoader(), new Class<?>[]{clazz},
            new IBatisProxy(hikariDataSource));
        return userDao;
    }

}

测试调用

@ RestController
public class HelloWorldController
{
    @ Autowired
    @ Qualifier("userDao2")
    private UserDao userDao;
    
    @ RequestMapping("/user/{id}")
    @ Transactional
    public com.inus.domain.User getUser(@ PathVariable String id)
    {
        if (StringUtils.isNotEmpty(id))
        {
            return userDao.getById(id);
        }
        
        return null;
    }
}

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