On the other hand, the ConcurrentTaskExecutor runs the same as the ThreadPoolTaskExecutor but in a more flexible manner. It has a decorator which is executed as a runnable task that can be utilized to add some monitoring and statistics for its task execution.

There is only one TaskExecutor that can be injected into the container implemented by AsyncConfigurer. This happens because we have only one method, getAsyncExecutor(), to override in order to inject that sole TaskExecutor appropriate for the applications.

This entire configuration will not be triggered without invoking the class-level @EnableAsync in the custom SpringAsyncConfig context definition. In the case that getAsyncExecutor() has not been overridden, it will inject SimpleAsyncTaskExecutor by default.