[JavaScript知识库]mybatis源码解析3_getMapper

注

以下内容都是根据尚硅谷2018年mybatis源码解析做的课程笔记，视频链接：
https://www.bilibili.com/video/BV1mW411M737?p=74&share_source=copy_web
另外特别感谢雷丰阳老师的讲解

拿到sqlSession，接下来就该getMapper了

SqlSession sqlSession=MybatisUtils.getSqlSession();
TypeDao dao=sqlSession.getMapper(TypeDao.class);

一路往下

    <T> T getMapper(Class<T> var1);

    public <T> T getMapper(Class<T> type) {
        return this.configuration.getMapper(type, this);
    }

    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        return this.mapperRegistry.getMapper(type, sqlSession);
    }

   public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
        if (mapperProxyFactory == null) {
            throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
        } else {
            try {
                return mapperProxyFactory.newInstance(sqlSession);
            } catch (Exception var5) {
                throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
            }
        }
    }

最终在this.mapperRegistry.getMapper方法真正实现了mapper
其中

return mapperProxyFactory.newInstance(sqlSession);

它new了一个Instance

    public T newInstance(SqlSession sqlSession) {
        MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
        return this.newInstance(mapperProxy);
    }

这里面又new了一个mapper的代理对象

而这个类又实现了动态代理

最后他调用本类的newInstance，这里面又调用了java本类的代理对象

    protected T newInstance(MapperProxy<T> mapperProxy) {
        return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
    }

所以我们最终拿到的mapper是mapperProxy的代理对象
返回的mapper又包含了sqlSession，最终才能用于增删改查