验证并发情况下的自定义订单流水号生成器是否会有重复

gistfile1.txt

// 验证并发情况下的自定义订单流水号生成器是否会有重复
// 订单流水号生成器
public static String getOrderNo(){
        String orderNo = "";
        String date = new SimpleDateFormat("yyMMddHHmmss").format(new Date());
        Integer math = new Random().nextInt(1000);
        orderNo = date+""+math;
        return orderNo;
}
// 验证代码
public static void main(String[] args) throws InterruptedException {
        int nThreads = 60; //并发数
        ExecutorService pool = Executors.newFixedThreadPool(nThreads);
        final CountDownLatch latch = new CountDownLatch(nThreads);
        final List<String> list = new CopyOnWriteArrayList<>(); //使用线程安全list 保存每次生成的订单流水号
        for (int i = 0; i < nThreads; i++) {
            pool.submit(new Runnable() {
                @Override
                public void run() {
                    String orderNo = getOrderNo();
                    list.add(orderNo);
                    latch.countDown();
                }
            });
        }
        latch.await(); //等待所有任务完成
        System.out.println(list.size()); 
        System.out.println(new HashSet<>(list).size()); //去重后的大小
        Map<String, Long> countMap = list.stream().collect(Collectors.groupingBy(s->s,Collectors.counting()));
        countMap.entrySet().forEach( e->{ //输出出现次数大于1次的订单流水号
            if(e.getValue()>1L)
                System.out.println(e.getKey() + " " +e.getValue());
        });
}

时间+随机数，肯定会出现重复的