Guava的ListenableFuture使用范例

ListenableFuture是对JDK的Future的封装和增强，为Future添加回调机制。 JDK8也新增了CompletableFuture类实现了相同的功能，范例见 https://chenjumin.iteye.com/blog/2437228 ，建议用JDK8自带的CompletableFuture类。

 

public class ListenableFutureTest {
    private static int threadCount = 5; //线程数
	private static AtomicInteger count = new AtomicInteger(0);
    private static CountDownLatch countDownLatch = new CountDownLatch(threadCount);;
	
	public static void main(String[] args) throws Exception {
		//将 ExecutorService 转为 ListeningExecutorService
		ListeningExecutorService executorService = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10));
        
		//提交多个任务
		List<ListenableFuture<Boolean>> futureList = new ArrayList<>();
		for(int i=0; i<threadCount; i++){
			ListenableFuture<Boolean> future = submitTask(executorService);
			futureList.add(future);
		}
		
		//堵塞方式获取所有任务的执行结果
		//如果任务出异常，会一直堵塞下去
//		System.out.println("堵塞等待执行结果...");
//		ListenableFuture<List<Boolean>> allFuture = Futures.allAsList(futureList);
//		allFuture.get(3000, TimeUnit.MILLISECONDS);
		
		countDownLatch.await();
		
        System.out.println("main task done");
        executorService.shutdown(); //等待task执行完后再shutdown
//        executorService.shutdownNow(); //停止执行中的task，立即shutdown
	}

	private static ListenableFuture<Boolean> submitTask(ListeningExecutorService executorService) {
		//提交Callable任务
		ListenableFuture<Boolean> future = executorService.submit(new Callable<Boolean>() {
			@Override
			public Boolean call() throws Exception {
				int t = 1000 + new Random().nextInt(2000);
				System.out.println(t);
				Thread.sleep(t);
				
				if(count.incrementAndGet() == 1){
					throw new RuntimeException();
				}
				
                return true;
			}
		});
		
		//为 ListenableFuture 注册回调方法(callback)
		Futures.addCallback(future, new FutureCallback<Boolean>() {
			/**
			 * Callable任务执行成功时回调该方法
			 */
			@Override
			public void onSuccess(Boolean b) {
				countDownLatch.countDown();
				System.out.println("task result=" + b);
			}
			
			/**
			 * Callable任务执行出现异常时回调该方法
			 */
			@Override
			public void onFailure(Throwable ex) {
				countDownLatch.countDown();
				System.out.println(ex.toString());
			}
		});
		
		return future;
	}
}