读mybatis源码之五：执行器Executor创建

         在sqlsession中主要是执行都是通过executor来处理的：

 executor.query(ms, wrapCollection(parameter), rowBounds, handler);

executor.update(ms, wrapCollection(parameter));

      执行器从哪里来呢？在DefaultSqlSessionFactory里面openSessionFromDataSource：

 final Executor executor = configuration.newExecutor(tx, execType, autoCommit);

看configuration里面怎么构建执行器的：

public Executor newExecutor(Transaction transaction, ExecutorType executorType, boolean autoCommit) {
    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);
    }
    if (cacheEnabled) {
      <span style="color:#ff0000;">executor = new CachingExecutor(executor, autoCommit);</span>
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

可以看到，默认是是简单执行器，还有批量、重用执行器，下面这段话解释不用的执行器使用方式：

executor = (Executor) interceptorChain.pluginAll(executor);  

是将执行器添加到拦截器中，这个很重要，为后续写插件提供时机。

具体为session指定执行器可以使用类似这种方式sessionFactory.openSession(ExecutorType.BATCH, false);