<bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">          <constructor-arg index="0" ref="sqlSessionFactory" />    </bean>

 1   public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, 2       PersistenceExceptionTranslator exceptionTranslator) { 3  4     notNull(sqlSessionFactory, "Property ‘sqlSessionFactory‘ is required"); 5     notNull(executorType, "Property ‘executorType‘ is required"); 6  7     this.sqlSessionFactory = sqlSessionFactory; 8     this.executorType = executorType; 9     this.exceptionTranslator = exceptionTranslator;10     this.sqlSessionProxy = (SqlSession) newProxyInstance(11         SqlSessionFactory.class.getClassLoader(),12         new Class[] { SqlSession.class },13         new SqlSessionInterceptor());14   }

 1   private class SqlSessionInterceptor implements InvocationHandler { 2     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 3       //获取SqlSession(这个SqlSession才是真正使用的，它不是线程安全的) 4       //这个方法可以根据Spring的事物上下文来获取事物范围内的sqlSession 5       //一会我们在分析这个方法 6       final SqlSession sqlSession = getSqlSession( 7           SqlSessionTemplate.this.sqlSessionFactory, 8           SqlSessionTemplate.this.executorType, 9           SqlSessionTemplate.this.exceptionTranslator);10       try {11         //调用真实SqlSession的方法12         Object result = method.invoke(sqlSession, args);13         //然后判断一下当前的sqlSession是否被Spring托管 如果未被Spring托管则自动commit14         if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {15           // force commit even on non-dirty sessions because some databases require16           // a commit/rollback before calling close()17           sqlSession.commit(true);18         }19         //返回执行结果20         return result;21       } catch (Throwable t) {22         //如果出现异常则根据情况转换后抛出23         Throwable unwrapped = unwrapThrowable(t);24         if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {25           Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);26           if (translated != null) {27             unwrapped = translated;28           }29         }30         throw unwrapped;31       } finally {32         //关闭sqlSession33         //它会根据当前的sqlSession是否在Spring的事物上下文当中来执行具体的关闭动作34         //如果sqlSession被Spring管理 则调用holder.released(); 使计数器-135         //否则才真正的关闭sqlSession36         closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);37       }38     }39   }

 1 public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {      2     //根据sqlSessionFactory从当前线程对应的资源map中获取SqlSessionHolder，当sqlSessionFactory创建了sqlSession，就会在事务管理器中添加一对映射：key为sqlSessionFactory，value为SqlSessionHolder，该类保存sqlSession及执行方式  3     SqlSessionHolder holder = (SqlSessionHolder) getResource(sessionFactory);  4  //如果holder不为空，且和当前事务同步  5     if (holder != null && holder.isSynchronizedWithTransaction()) {  6       //hodler保存的执行类型和获取SqlSession的执行类型不一致，就会抛出异常，也就是说在同一个事务中，执行类型不能变化，原因就是同一个事务中同一个sqlSessionFactory创建的sqlSession会被重用  7       if (holder.getExecutorType() != executorType) {  8         throw new TransientDataAccessResourceException("Cannot change the ExecutorType when there is an existing transaction");  9       } 10       //增加该holder,也就是同一事务中同一个sqlSessionFactory创建的唯一sqlSession，其引用数增加，被使用的次数增加 11       holder.requested(); 12    //返回sqlSession 13       return holder.getSqlSession(); 14     } 15  //如果找不到，则根据执行类型构造一个新的sqlSession 16     SqlSession session = sessionFactory.openSession(executorType); 17  //判断同步是否激活，只要SpringTX被激活，就是true 18     if (isSynchronizationActive()) { 19    //加载环境变量，判断注册的事务管理器是否是SpringManagedTransaction，也就是Spring管理事务 20       Environment environment = sessionFactory.getConfiguration().getEnvironment(); 21       if (environment.getTransactionFactory() instanceof SpringManagedTransactionFactory) { 22   //如果是，则将sqlSession加载进事务管理的本地线程缓存中 23         holder = new SqlSessionHolder(session, executorType, exceptionTranslator); 24   //以sessionFactory为key，hodler为value，加入到TransactionSynchronizationManager管理的本地缓存ThreadLocal<Map<Object, Object>> resources中 25         bindResource(sessionFactory, holder); 26   //将holder, sessionFactory的同步加入本地线程缓存中ThreadLocal<Set<TransactionSynchronization>> synchronizations 27         registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory)); 28         //设置当前holder和当前事务同步 29   holder.setSynchronizedWithTransaction(true); 30   //增加引用数 31         holder.requested(); 32       } else { 33         if (getResource(environment.getDataSource()) == null) { 34         } else { 35           throw new TransientDataAccessResourceException( 36               "SqlSessionFactory must be using a SpringManagedTransactionFactory in order to use Spring transaction synchronization"); 37         } 38       } 39     } else { 40     } 41     return session; 42   } 

 1 public static void closeSqlSession(SqlSession session, SqlSessionFactory sessionFactory) {  2  //其实下面就是判断session是否被Spring事务管理，如果管理就会得到holder   3     SqlSessionHolder holder = (SqlSessionHolder) getResource(sessionFactory);  4     if ((holder != null) && (holder.getSqlSession() == session)) {  5    //这里释放的作用，不是关闭，只是减少一下引用数，因为后面可能会被复用  6       holder.released();  7     } else {  8    //如果不是被spring管理，那么就不会被Spring去关闭回收，就需要自己close  9       session.close(); 10     } 11   }