@Async自带的线程池导致的oom

        我们平常如果想使用spring自带的线程池，可以使用@EnableAsync,然后在需要异步调用的方法上加上@Async即可异步调用。但是spring调用异步方法的默认的线程池

SimpleAsyncTaskExecutor却并不是真正意义上的线程池，它会为每一个任务都创建一个线程，这样当我们一次性有很多的任务来时，就会创建大量的线程，可能造成OOM.

/**
 * {@link TaskExecutor} implementation that fires up a new Thread for each task,
 * executing it asynchronously.
 *
 * <p>Supports limiting concurrent threads through the "concurrencyLimit"
 * bean property. By default, the number of concurrent threads is unlimited.
 *
 * <p><b>NOTE: This implementation does not reuse threads!</b> Consider a
 * thread-pooling TaskExecutor implementation instead, in particular for
 * executing a large number of short-lived tasks.
 *
 * @author Juergen Hoeller
 * @since 2.0
 * @see #setConcurrencyLimit
 * @see SyncTaskExecutor
 * @see org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor
 * @see org.springframework.scheduling.commonj.WorkManagerTaskExecutor
 */