Java CompletableFuture：allOf等待所有异步线程任务结束

   private void method() throws ExecutionException, InterruptedException {
        CompletableFuture<String> f1 = CompletableFuture.supplyAsync(() -> {
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
 
            return "f1";
        });
 
        f1.whenCompleteAsync(new BiConsumer<String, Throwable>() {
            @Override
            public void accept(String s, Throwable throwable) {
                System.out.println(System.currentTimeMillis() + ":" + s);
            }
        });
 
        CompletableFuture<String> f2 = CompletableFuture.supplyAsync(() -> {
            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
 
            return "f2";
        });
 
        f2.whenCompleteAsync(new BiConsumer<String, Throwable>() {
            @Override
            public void accept(String s, Throwable throwable) {
                System.out.println(System.currentTimeMillis() + ":" + s);
            }
        });
 
        CompletableFuture<Void> all = CompletableFuture.allOf(f1, f2);
 
        //阻塞，直到所有任务结束。
        System.out.println(System.currentTimeMillis() + ":阻塞");
        all.join();
        System.out.println(System.currentTimeMillis() + ":阻塞结束");
 
        //一个需要耗时2秒，一个需要耗时3秒，只有当最长的耗时3秒的完成后，才会结束。
        System.out.println("任务均已完成。");
    }

06-12 20:16:37.400 31142-31142/zhangphil.test I/System.out: 1528805797400:阻塞
06-12 20:16:39.406 31142-31171/zhangphil.test I/System.out: 1528805799406:f2
06-12 20:16:40.404 31142-31170/zhangphil.test I/System.out: 1528805800404:f1
06-12 20:16:40.404 31142-31142/zhangphil.test I/System.out: 1528805800404:阻塞结束
任务均已完成。