【java】【多线程】等待并行无关任务获取整体结果

【方案一】java8流式实现

       
        List root = roleDao.selRootPermission(roleReq.getApplicationId());//获取应用所有根节点权限

List> completableFutureList = root.stream()
                .map(permission -> CompletableFuture.supplyAsync(() -> {
                    System.out.println("------cu------" + Thread.currentThread().getName() + "*****" + Thread.currentThread().getId());
                    try {
                        cycle(permission);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return permission;
                }))  //格式转换
                .collect(Collectors.toList());

        return completableFutureList.stream().map(CompletableFuture::join).collect(Collectors.toList());

【方案二】

CountDownLatch 中有一个计数器字段，在对象创建时初始化，表示需要等待的事件数量。countDown() 方法递减计数器，表示有一个事件已经发生了，await() 方法等待计数器为 0 时，表示所有的需要等待的时间都已经发生。如果计数器的值非 0 会一直阻塞直到计数器为 0

        List root = roleDao.selRootPermission(roleReq.getApplicationId());//获取应用所有根节点权限

        //主线程阻塞，直到所有分线程执行完毕
        CountDownLatch end = new CountDownLatch(root.size());

        List total = new ArrayList<>();

        for (PermissionTree permission : root) {
            CompletableFuture future = CompletableFuture.runAsync(() -> {
                try {
                    cycle(permission);//递归找出所有子节点权限
//                    System.out.println("int" + Thread.currentThread().getName());
                } catch (Exception e) {
                    e.printStackTrace();
                }
                total.add(permission);
                end.countDown();
            });

//            System.out.println("out2" + Thread.currentThread().getName());
        }
        end.await();
//        System.out.println("out3" + Thread.currentThread().getName());
        return total;

 

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