咱们直入主题，分析源码吧！从获取Mapper开始吧。
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);public <T> T getMapper(Class<T> type) { return configuration.getMapper(type, this); }
mapperRegistry.getMapper是从MapperRegistry的knownMappers里面取的,knownMappers里面存的是接口类型(interface mapper.UserMapper)和工厂类(MapperProxyFactory)。
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { return mapperRegistry.getMapper(type, sqlSession); }
从knownMappers的Map里根据接口类型(interface mapper.UserMapper)取出对应的工厂类
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>)knownMappers.get(type); if (mapperProxyFactory == null) { throw new BindingException("Type " + type + " is not known to the MapperRegistry."); } try { return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } } public T newInstance(SqlSession sqlSession) { final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }
这里通过JDK动态代理返回代理对象MapperProxy。