1.用户使用

1.提供 xxMapper接口

public interface UserMapper {
    @Select(value = "select * from user where id=#{id}")//（1）注解方式
    public User getUser(Long id);
}

2.在xml里配置（可选配置）（2）

<mapper namespace="org.wangying.dao.UserDao">
    <select id="getUser" resultType="org.wangying.entity.User" parameterType="Long">
        select * from user where id=#{id}
    </select>
</mapper>

2.mybatis实现

在调用sqlSession.getMapper(Class)发生了一些神奇的事情

DefaultSqlSession.getMapper(type)
    Configuration.getMapper(type,sqlSession)
        MapperRegistry.getMapper(type,sqlSession) //存放键值对type（接口）-MapperProxyFactory
            MapperProxyFactory.newInstance(sqlSession)
                mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);//代理对象
                MapperProxyFactory.newInstance(mapperProxy)
                    Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy)//生成了一个代理实例，返回

1.实现了对应的接口
mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
2.使用Proxy生成了一个代理实例
Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy)

动态代理实现

MapperProxy 实现InvocationHandler
在invoke方法中从sqlSession的configuration中获取sql语句，
根据sql语句生成方法（jdbc的prepareStatement）

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);//从sqlSession的configuration中获取sql语句，根据sql语句生成方法（jdbc的prepareStatement）
    return mapperMethod.execute(sqlSession, args);//执行映射成的方法
  }