讀mybatis源碼之五：執行器Executor創建

         在sqlsession中主要是執行都是通過executor來處理的：

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

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

      執行器從哪裏來呢？在DefaultSqlSessionFactory裏面openSessionFromDataSource：

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

看configuration裏面怎麼構建執行器的：

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，默認是是簡單執行器，還有批量、重用執行器，下面這段話解釋不用的執行器使用方式：

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

是將執行器添加到攔截器中，這個很重要，爲後續寫插件提供時機。

具體爲session指定執行器可以使用類似這種方式sessionFactory.openSession(ExecutorType.BATCH, false);