七天带你入门Mybatis源码第四天，MappedStatement

以你之姓@ 2023-02-15 10:08 36阅读 0赞

有了前三讲的基础，我们知道mybatis的架构，mybatis的xml解析，Configuration的解析等知识的奠基。我们今天就来深刻探讨一下MappedStatement是个啥东西，有啥作用。

我们现在来思考一下，看下这两个东西：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70][]

我们写的一个接口和这个xml的mapper文件，是怎样结合起来的？

我们只要用过mybatis，我们应该都知道mybatis有一个这样的一个流程：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 1][]

我们就从源码的角度来看待这个问题吧

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 2][]

这个截图，我们在第三讲是有截图的，就是解析了XML之后，会得到这些参数信息，最后利用建造者模式builder出来，最后把这个MappedStatement放在Configuration中

![2020060423112461.png][]

我们可以猜测一个这个ms.getId()是什么东西？

没错，正是我们的namespace+我们接口的方法名，这样就能把我们的接口和mapper的xml关联在一起了。

我们的sqlSessionFactory就算是构建完成了，下面就要掉我们的openSession来打开我们的openSession了，进去看一看

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 3][]

有了SqlSession之后，我们就可以调用获取我们的Mapper了

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 4][]

从我们之前添加的mapper的那个map中，获取到这个mapper，最后利用jdk的动态代理，返会一个代理对象

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 5][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 6][]

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就这样这个这个代理对象就被弄出来了，底层就用了jdk的动态代理来实现的，so easy吧

解决了这个疑惑，我们来看下MappedStatement的构建吧

我们在addMapper的时候

![20200607224603102.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 8][]

我们会执行parser.parse();

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 9][]

我们这上面几天SqlSessionFactory和SqlSession的构建，我们应该已经很熟悉了，今天我们就重点看下

BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);是怎样生成的

从configuration对象中把mapper获取到

![20200608220341584.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 10][]

我们之前看过，这个是一个代理对象,执行invoke方法,看下execute方法

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 11][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L29sZHNoYXVp_size_16_color_FFFFFF_t_70 12][]

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