mybatismapper 怎么实现动态代理的调用思路 使用代码实现一下

MyBatis Mapper 实现动态代理的调用思路：

1. 定义 Mapper 接口，该接口可以通过注解或 XML 文件的方式定义 SQL 语句和参数映射关系。
2. 使用 MyBatis 的 MapperFactory 创建 MapperProxyFactory 对象，该对象用于创建 Mapper 接口的代理对象。
3. 创建 MapperProxy 对象，该对象实现了 InvocationHandler 接口，用于处理代理对象方法的调用。
4. 通过 MapperProxyFactory 对象的 newInstance 方法创建 Mapper 接口的代理对象，该对象会被传入 MapperProxy 对象的构造函数中。
5. 通过代理对象调用 Mapper 接口的方法时，会被 MapperProxy 对象的 invoke 方法拦截，该方法会根据方法名和参数类型动态生成 SQL 语句，并通过 MyBatis 的 SqlSession 执行 SQL 语句。

下面是使用 Java 代码实现 MyBatis Mapper 动态代理的调用过程：

1. 定义 Mapper 接口

public interface UserMapper {
    @Select("SELECT * FROM users WHERE id = #{id}")
    User getUserById(int id);
}

2. 创建 MapperProxyFactory 对象

public class MapperFactory {
    private final Configuration configuration;
    
    public MapperFactory(Configuration configuration) {
        this.configuration = configuration;
    }
    
    public <T> T getMapper(Class<T> mapperInterface) {
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(),
                new Class[]{mapperInterface},
                new MapperProxy(configuration, mapperInterface));
    }
}

3. 创建 MapperProxy 对象

public class MapperProxy<T> implements InvocationHandler {
    private final SqlSession sqlSession;
    private final Class<T> mapperInterface;
    
    public MapperProxy(Configuration configuration, Class<T> mapperInterface) {
        this.sqlSession = new SqlSessionFactoryBuilder().build(configuration).openSession();
        this.mapperInterface = mapperInterface;
    }
    
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        String statement = mapperInterface.getName() + "." + method.getName();
        MappedStatement mappedStatement = sqlSession.getConfiguration().getMappedStatement(statement);
        if (mappedStatement == null) {
            throw new RuntimeException("Can't find mapped statement for " + statement);
        }
        Object result = null;
        switch (mappedStatement.getSqlCommandType()) {
            case SELECT:
                result = sqlSession.selectOne(statement, args);
                break;
            case INSERT:
                result = sqlSession.insert(statement, args);
                break;
            case UPDATE:
                result = sqlSession.update(statement, args);
                break;
            case DELETE:
                result = sqlSession.delete(statement, args);
                break;
            default:
                throw new RuntimeException("Unknown SqlCommandType " + mappedStatement.getSqlCommandType());
        }
        sqlSession.commit();
        return result;
    }
}

4. 创建 Mapper 接口的代理对象

Configuration configuration = new Configuration();
configuration.addMapper(UserMapper.class);
MapperFactory mapperFactory = new MapperFactory(configuration);
UserMapper userMapper = mapperFactory.getMapper(UserMapper.class);

5. 调用 Mapper 接口的方法

User user = userMapper.getUserById(1);