java多线程执行有返回值的任务示例

public static void main(String[] args) throws Exception {

        long startTime = System.currentTimeMillis();

        //ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
        Map<String, String> map = new HashMap<>();

        ExecutorService executorService = Executors.newFixedThreadPool(10);
        //final BlockingQueue<Future<String>> queue = new LinkedBlockingDeque<>(10);
        //实例化CompletionService
        //final CompletionService<String> completionService = new ExecutorCompletionService<>(executorService, queue);

        //for (int i = 0; i < 10; i++) {
        //    int finalI = i;
        //    executorService.submit(new Callable<String>() {
        //        public String call() {
        //            return getResult(finalI);
        //        }
        //    });
        //}
        //
        //// 输出结果
        //for (int i = 0; i < 10; i++) {
        //    // 获取包含返回结果的future对象
        //    // （若整个阻塞队列中还没有一条线程返回结果，那么调用take将会被阻塞，
        //    // 当然你可以调用poll，不会被阻塞，若没有结果会返回null，poll和take返回正确的结果后会将该结果从队列中删除）
        //    Future<String> future = completionService.take();
        //    // 从future中取出执行结果，这里存储的future已经拥有执行结果，get不会被阻塞
        //    String result = future.get();
        //    System.out.println(result);
        //}
        //executorService.shutdown();

        //for (int i = 0; i < 10; i++) {
        //    int finalI = i;
        //    executorService.submit(() -> {
        //        String result = getResult(finalI);
        //        map.put(String.valueOf(finalI), result);
        //    });
        //}
        //
        //executorService.shutdown();
        //while (!executorService.isTerminated()){
        //    Thread.sleep(1000);
        //    System.out.println("还没停止。。。");
        //}
        //System.out.println("全部执行完毕");


        List<CompletableFuture<Void>> futures = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            int finalI = i;
            CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(() -> {
                String result = getResult(finalI);
                map.put(String.valueOf(finalI), result);
            }, executorService);
            futures.add(completableFuture);
        }
        CompletableFuture.allOf(futures.toArray(new CompletableFuture[futures.size()])).join();
        executorService.shutdown();

        //for (int i = 0; i < 10; i++) {
        //    String result = getResult(i);
        //    map.put(String.valueOf(i), result);
        //}

        System.out.println("大小：" + map.size());
        //System.out.println(map);

        long endTime = System.currentTimeMillis();
        System.out.println("耗时：" + (endTime - startTime));
    }

    public static String getResult(int i) {
        try {
            Thread.sleep(new Random().nextInt(500));
            System.out.println(i);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        String result = "当前值：" + i;
        return result;
    }

 

参考：http://www.bryh.cn/a/388436.html、https://blog.csdn.net/hkk666123/article/details/131946695