6.CountDownLatch

CountDownLatch

用来进行线程间的同步协作，等待所有线程完成倒计时

其中构造参数用来初始化等待计数值，await()用来等待计数归零，countDown()用来让计数减一

可以让主线程等待线程池中的所有线程执行完毕再运行

例如：王者荣耀游戏需要等所有玩家加载完毕才能开始

private static void test2() throws InterruptedException {
    AtomicInteger num = new AtomicInteger(0);
    ExecutorService service = Executors.newFixedThreadPool(10, (r) -> {
        return new Thread(r, "t" + num.getAndIncrement());
    });
    CountDownLatch latch = new CountDownLatch(10);
    String[] all = new String[10];
    Random r = new Random();
    for (int j = 0; j < 10; j++) {
        int x = j;
        service.submit(() -> {
            for (int i = 0; i <= 100; i++) {
                try {
                    Thread.sleep(r.nextInt(100));
                } catch (InterruptedException e) {
                }
                all[x] = Thread.currentThread().getName() + "(" + (i + "%") + ")";
                System.out.print("\r" + Arrays.toString(all));
            }
            latch.countDown();
        });
    }
    latch.await();
    System.out.println("\n游戏开始...");
    service.shutdown();
}

future：

利用future让主线程获取其他多线程运行的返回结果

private static void test3() throws InterruptedException, ExecutionException {
    RestTemplate restTemplate = new RestTemplate();
    log.debug("begin");
    ExecutorService service = Executors.newCachedThreadPool();
    CountDownLatch latch = new CountDownLatch(4);
    Future<Map<String, Object>> f1 = service.submit(() -> {
        Map<String, Object> response = restTemplate.getForObject("http://localhost:8080/order/{1}", Map.class, 1);
        return response;
    });
    Future<Map<String, Object>> f2 = service.submit(() -> {
        Map<String, Object> response1 = restTemplate.getForObject("http://localhost:8080/product/{1}", Map.class, 1);
        return response1;
    });
    Future<Map<String, Object>> f3 = service.submit(() -> {
        Map<String, Object> response1 = restTemplate.getForObject("http://localhost:8080/product/{1}", Map.class, 2);
        return response1;
    });
    Future<Map<String, Object>> f4 = service.submit(() -> {
        Map<String, Object> response3 = restTemplate.getForObject("http://localhost:8080/logistics/{1}", Map.class, 1);
        return response3;
    });
    System.out.println(f1.get());
    System.out.println(f2.get());
    System.out.println(f3.get());
    System.out.println(f4.get());
    log.debug("执行完毕");
    service.shutdown();
}