MyBatis 3源码解析(二)

二、获取SqlSession对象

1.首先调用DefaultSqlSessionFactory 的 openSession 方法，代码如下：

  @Override
  public SqlSession openSession() {
    //configuration.getDefaultExecutorType 是调用configuration的Executor执行器的类型，默认simple
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
  }

• 下面是openSessionFromDataSource方法：

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
       //从configuration中获取环境配置信息
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      //获取一些信息，创建了一个事物
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      //根据Executor在configuration中的配置，创建一个新的Executor
      final Executor executor = configuration.newExecutor(tx, execType);
      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();
    }
  }

创建Executor的代码如下：

  public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
      executor = new ReuseExecutor(this, transaction);
    } else {
      executor = new SimpleExecutor(this, transaction);
    }
    //如果二级缓存配置开启了，创建CachingExecutor
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

最后返回了DefaultSqlSession，DefaultSqlSession中包含配置信息。

总结：返回SqlSession的实现类DefaultSqlSession对象。他里面包含了Executor和Configuration；Executor会在这一步被创建