Mybatis SqlSessionTemplate 源码解析

    <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commit
14         if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
15           // force commit even on non-dirty sessions because some databases require
16           // 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sqlSession
33         //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-1
35         //否则才真正的关闭sqlSession
36         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   }