关于mybatis的执行过程的简单分析（三）

喜欢ヅ旅行 2022-01-30 08:51 214阅读 0赞

#### 第三步分析：.sqlSession.getMapper(DepartmentMapper.class)获得mapper ####

`sqlSession.getMapper(DepartmentMapper.class)`debug方式进行探索，先进去方法体：  
**如图\#3.1**  
![在这里插入图片描述][20190518163820942.png]  
**接着再往下走图\#3.2**  
![在这里插入图片描述][20190518163923211.png]  
这里里调用 mapperRegistry.getMapper（）方法，进入，往下走  
\*\* 图\#3.3\*\*

@SuppressWarnings("unchecked")
      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);
        }
      }

1.`MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type)`先获得mapperProxyFactory 工厂  
2.`return mapperProxyFactory.newInstance(sqlSession)` 执行.newInstance(sqlSession)方法然后返回，进入看一下`newInstance(sqlSession)`的执行过程。

@SuppressWarnings("unchecked")
      protected T newInstance(MapperProxy<T> mapperProxy) { 
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] {  mapperInterface }, mapperProxy);//#3
      }
    
      public T newInstance(SqlSession sqlSession) { 
        final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);// #1
        return newInstance(mapperProxy);	//#2
      }

代码\#3,先创建一个`mapperProxy`我看一下这个`mapperProxy`是什么东西，点击去看看 。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70]  
注意实现了`InvocationHandler`接口，这个比较熟悉，是用来创建动态代理的，。

接着执行代码\#2，

protected T newInstance(MapperProxy<T> mapperProxy) { 
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] {  mapperInterface }, mapperProxy);//#3
      }

**小结：  
执行了Proxy.newProxyInstance（）方法，创建了动态代理对象，然后返回，然后逐步返回，就获得了我们要的Mapper接口对象，动态代理对象里面包含SqlSession 然后SqlSession里边又包含我们的执行器exectour,那么我们的第四个步骤就能使用我们的执行器，进行查询操作**  
同样，我也画一下时序图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70 1]

[20190518163820942.png]: /images/20220130/d77795711a1c4982b225873b9e06ab62.png
[20190518163923211.png]: /images/20220130/9f3edd35da6a4dc5a8ceca8410e6e433.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70]: /images/20220130/ac473d342c014e8f9abaf9cf64971b41.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70 1]: /images/20220130/db78a43a6169440eb60d405e0c424508.png