20210826

public class SnowFlake {
    public static long getId() {
        String s = "0" + getTimestampInBitStr() + getMachineIdInBitStr() + getSeqInBitStr();
        return Long.parseLong(s, 2);
    }

    /**
     * 获得41位时间戳的01字符串
     *
     * @return 例如 10100111101110010010110000011001111011001  共41位
     */
    private static String getTimestampInBitStr() {
        Long _100YearsInMillis = 189216000000L;// 100*365*24*60*60*60 即100年
        long currentTimeMillis = System.currentTimeMillis();
        long timeMillis = currentTimeMillis - _100YearsInMillis;// 为了使时间戳能多用100年
        return Long.toString(timeMillis, 2);
    }

    /**
     * 获得10位的机器id,机器id可以从配置文件中读取，
     * 每台机器的机器id配置成不同的
     */
    private static String getMachineIdInBitStr() {
        return "0000000001";// TODO
    }

    /**
     * 获得12位的序列
     * 可以使用随机的方式
     */
    private static String getSeqInBitStr() {
        String seq = "";
        Random random = new Random();
        for (int i = 0; i < 12; i++) seq += random.nextInt(2);
        return seq;
    }
}

测试代码

public class SnowFlakeTest {
    public static void main(String[] args) {
        Set<Long> set = new CopyOnWriteArraySet<>();
        ThreadPoolExecutor pool = new ThreadPoolExecutor(20,
                100,
                10,
                TimeUnit.MICROSECONDS,
                new ArrayBlockingQueue<>(2),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.DiscardPolicy()
        );

        for (int i = 0; i < 10000; i++) {
            pool.execute(() -> {
                long id = SnowFlake.getId();
                if (set.contains(id))
                    System.out.println("重复=>" + id + ",threadName=>" + Thread.currentThread().getName());
                else set.add(id);
            });
        }
    }
}

发现会出现重复id,并发1万时只有1~2次重复

重复=>6042929485324490319,threadName=>pool-1-thread-5