Mybaits源码分析八之sqlSessiion的openSession方法

mybatis的Demo案例中  ,通过sqlSessionFactory创建Session

 //通过sqlSessionFactory创建SqlSession
    public static SqlSession getSession(){
        return sqlSessionFactory.openSession();
    }

  @Override
  public SqlSession openSession(boolean autoCommit) {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, autoCommit);
  }

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
     //获取environment对象，就是mybatis配置中的environment子节点下的配置内容
      final Environment environment = configuration.getEnvironment();
     //构建事务工厂
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
    //创建事务实例
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
    //创建一个执行器
      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();
    }
  }

 configuration.newExecutor(tx, execType);为创建一个执行器，创建执行器的过程为：

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    //获取默认的执行器类型，默认为SIMPLE
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
   //执行器类型为三种BATCH 批量执行已经预编译的sql，REUSE 重复执行sql，SIMPLE只执行一次
    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);
    }
    //判断是否开启缓存，默认是开启的
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }