mybatis源码(二) mapper代理生成,sqlsession生成

Love The Way You Lie 2022-12-03 08:55 177阅读 0赞

### 文章目录 ###

*   *  回顾
     *  SqlSession的生成
     *   *  生成执行器Executor方法
     *  再看看SqlSession
     *   *  getMapper方法

## 回顾 ##

上一篇讲了DefaultSqlSessionFactory类的生成,主要讲的就是maybatis配置文件的解析,mapper的解析,然后根据Configuration生成SqlSessionFactory;  
**这一篇我们讲前面提到的SqlSession.和mapper的生成**.

## SqlSession的生成 ##

还是前面的小例子,前面创建了SqlSessionFactory,SqlSessionFactory有个方法openSession返回SqlSession;  
我们看DefaultSqlSessionFactory的openSession方法:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MzY2MDYz_size_16_color_FFFFFF_t_70_pic_center]  
再看具体方法:

/** * execType执行器类型,默认是ExecutorType.simple * * level 事务隔离级别,默认null * * autoCommit是否自动提交,默认false * protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE; * @Override * public SqlSession openSession() { * return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false); * } * * @param execType * @param level * @param autoCommit * @return */
      private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) { 
        Transaction tx = null;
        try { 
          //获取环境信息
          final Environment environment = configuration.getEnvironment();
          //根据环境信息返回事务工厂,我们使用spring进行管理,返回的是SpringManagedTransactionFactory
          final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
          //根据数据源,事务隔离级别,是否自动提交生成事务管理器,返回的是Spring的事物SpringManagedTransaction
          tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
          //根据事务和执行器类别生成执行器,二级缓存默认打开,这里的SimpleExecutor会被包装成CacheExecutor
          final Executor executor = configuration.newExecutor(tx, execType);
          //返回默认的sqlsession
          return new DefaultSqlSession(configuration, executor, autoCommit);
        } catch (Exception e) { 
          closeTransaction(tx); // may have fetched a connection so lets call close()
          throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
        } finally { 
          ErrorContext.instance().reset();
        }
      }

### 生成执行器Executor方法 ###

public Executor newExecutor(Transaction transaction, ExecutorType executorType) { 
        //如果为null,则设置为默认的tyoe,就是ExecutorType.SIMPLE
        executorType = executorType == null ? defaultExecutorType : executorType;
        //如果还是为null,则手动设置为ExecutorType.SIMPLE
        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
        Executor executor;
        if (ExecutorType.BATCH == executorType) { 
          // batch开头的想必大家不陌生了,批量操作
          executor = new BatchExecutor(this, transaction);
        } else if (ExecutorType.REUSE == executorType) { 
          //复用预处理语句
          executor = new ReuseExecutor(this, transaction);
        } else { 
          //simple简单的执行器
          executor = new SimpleExecutor(this, transaction);
        }
        if (cacheEnabled) { 
          //是否开启二级缓存,封装为CachingExecutor
          executor = new CachingExecutor(executor);
        }
        //执行一次所有拦截方法
        executor = (Executor) interceptorChain.pluginAll(executor);
        return executor;
      }

interceptorChain的实现也比较简单,就是将所有拦截器放到list里面,循环调用:

public class InterceptorChain { 
    
      private final List<Interceptor> interceptors = new ArrayList<>();
    
      public Object pluginAll(Object target) { 
        for (Interceptor interceptor : interceptors) { 
          target = interceptor.plugin(target);
        }
        return target;
      }
    
      public void addInterceptor(Interceptor interceptor) { 
        interceptors.add(interceptor);
      }
    
      public List<Interceptor> getInterceptors() { 
        return Collections.unmodifiableList(interceptors);
      }
    
    }

## 再看看SqlSession ##

前面openSession的时候,根据configuration,执行器,是否自动提交生成了默认的SqlSession:

return new DefaultSqlSession(configuration, executor, autoCommit);
    
    // 这是sqlSession的属性
    public class DefaultSqlSession implements SqlSession { 
    
    //mybatis配置文件,mapper信息
      private final Configuration configuration;
      //执行器
      private final Executor executor;
    //自动提交
      private final boolean autoCommit;
      //记录本次executor执行过程中是否有过更改操作
      private boolean dirty;
      //游标,,具体没研究
      private List<Cursor<?>> cursorList;
    
      public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) { 
        this.configuration = configuration;
        this.executor = executor;
        this.dirty = false;
        this.autoCommit = autoCommit;
      }

看一下sqlsession的方法,主要是增删改查,还有获取mapper方法:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MzY2MDYz_size_16_color_FFFFFF_t_70_pic_center 1]

### getMapper方法 ###

上篇文章其实大部分讲过了,因为getMapper方法走的是configuration的getMapper方法,前面解析mapper文件的时候,也是解析xml的namespace类,将类加到MapperRegistry里面:

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MzY2MDYz_size_16_color_FFFFFF_t_70_pic_center 2]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MzY2MDYz_size_16_color_FFFFFF_t_70_pic_center 3]  
通过属性knownMappers获取到对应的maooer代理工厂类,然后通过MapperProxyFactory类生成对应的mapper代理;Proxy.newProxyInstance是通过jdk动态代理生成代理类的,详情可以了解:[https://blog.csdn.net/qq\_38366063/article/details/105298512][https_blog.csdn.net_qq_38366063_article_details_105298512]

public class MapperProxyFactory<T> { 
    
      private final Class<T> mapperInterface;
      private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<>();
    
      public MapperProxyFactory(Class<T> mapperInterface) { 
        this.mapperInterface = mapperInterface;
      }
    
      public Class<T> getMapperInterface() { 
        return mapperInterface;
      }
    
      public Map<Method, MapperMethod> getMethodCache() { 
        return methodCache;
      }
    
      @SuppressWarnings("unchecked")
      protected T newInstance(MapperProxy<T> mapperProxy) { 
        //根据mapperProxy生成代理,
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] {  mapperInterface }, mapperProxy);
      }
    
      public T newInstance(SqlSession sqlSession) { 
        //根据传入的sqlsession生成mapperProxy类,mapperProxy类必须实现InvocationHandler接口;
        final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
        return newInstance(mapperProxy);
      }
    
    }

而新建的MapperProxy类就是实现了InvocationHandler接口的具体执行方法的类;具体怎么执行,下次在讲,到这里,mapper代理就生成了;而通过spring结合mybatis的是通过往spring容器注入对应接口的方式,详见:  
[https://blog.csdn.net/qq\_38366063/article/details/108120233][https_blog.csdn.net_qq_38366063_article_details_108120233]

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[https_blog.csdn.net_qq_38366063_article_details_105298512]: https://blog.csdn.net/qq_38366063/article/details/105298512
[https_blog.csdn.net_qq_38366063_article_details_108120233]: https://blog.csdn.net/qq_38366063/article/details/108120233