public class FutureBlockTest {
    public static void main(String[] args) {
        // 為了模擬我這里只存創(chuàng)建一個工作線程
        ExecutorService fixedThreadPool = Executors.newFixedThreadPool(1);
        // 第一層異步任務
        Runnable runnable = () -> {
            System.out.println(Thread.currentThread().getName() + "-main-thread");
            // 第二層異步任務（嵌套任務）
            FutureTask<Long> futureTask = new FutureTask<>(() -> {
                System.out.println(Thread.currentThread().getName() + "-child-thread");
                return 10L;
            });
            fixedThreadPool.execute(futureTask);
            System.out.println("子任務提交完畢");

            // 獲取子線程的返回值
            try {
                System.out.println(futureTask.get());
            } catch (Exception e) {
                e.printStackTrace();
            }
        };
        // 提交主線
        fixedThreadPool.submit(runnable);
    }
}

// 程序入口
@Controller
public class AsyncController {
    @Autowired
    private MainThreadService mainThreadService;

    @GetMapping("/")
    public String helloWorld() throws Exception {
        mainThreadService.asyncMethod();
        return "Hello World";
    }
}

// 主任務代碼
@Service
public class MainThreadService {
    @Autowired
    private ChildThreadService childThreadService;

    @Async("asyncThreadPool")
    public void asyncMethod() throws Exception {
        // 主任務開始
        // TODO
        // 開啟子任務
        Future<Long> longFuture = childThreadService.asyncMethod();
        // 子任務阻塞子任務
        longFuture.get();
        // TODO
    }
}
// 子任務示例
@Service
public class ChildThreadService {
    @Async("asyncThreadPool")
    public Future<Long> asyncMethod() throws Exception {
        // 子任務執(zhí)行
        Thread.sleep(1000);
        // 返回異步結(jié)果
        return new AsyncResult<>(10L);
    }
}

jstack 81173 | grep 'WAITING' -A 15

	/**
	 * This implementation searches for a unique {@link org.springframework.core.task.TaskExecutor}
	 * bean in the context, or for an {@link Executor} bean named "taskExecutor" otherwise.
	 * If neither of the two is resolvable (e.g. if no {@code BeanFactory} was configured at all),
	 * this implementation falls back to a newly created {@link SimpleAsyncTaskExecutor} instance
	 * for local use if no default could be found.
	 * @see #DEFAULT_TASK_EXECUTOR_BEAN_NAME
	 */
	@Override
	protected Executor getDefaultExecutor(BeanFactory beanFactory) {
		Executor defaultExecutor = super.getDefaultExecutor(beanFactory);
		return (defaultExecutor != null ? defaultExecutor : new SimpleAsyncTaskExecutor());
	}

	/**
	 * Template method for the actual execution of a task.
	 * <p>The default implementation creates a new Thread and starts it.
	 * @param task the Runnable to execute
	 * @see #setThreadFactory
	 * @see #createThread
	 * @see java.lang.Thread#start()
	 */
	protected void doExecute(Runnable task) {
		Thread thread = (this.threadFactory != null ? this.threadFactory.newThread(task) : createThread(task));
		thread.start();
	}