public class SnowIdUtils {
    /**
     * 私有的 靜態(tài)內(nèi)部類
     */
    private static class SnowFlake {

        /**
         * 內(nèi)部類對(duì)象（單例模式）
         */
        private static final SnowIdUtils.SnowFlake SNOW_FLAKE = new SnowIdUtils.SnowFlake();
        /**
         * 起始的時(shí)間戳
         */
        private final long START_TIMESTAMP = 1557489395327L;
        /**
         * 序列號(hào)占用位數(shù)
         */
        private final long SEQUENCE_BIT = 12;
        /**
         * 機(jī)器標(biāo)識(shí)占用位數(shù)
         */
        private final long MACHINE_BIT = 10;
        /**
         * 時(shí)間戳位移位數(shù)
         */
        private final long TIMESTAMP_LEFT = SEQUENCE_BIT + MACHINE_BIT;
        /**
         * 最大序列號(hào)  （4095）
         */
        private final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
        /**
         * 最大機(jī)器編號(hào) （1023）
         */
        private final long MAX_MACHINE_ID = ~(-1L << MACHINE_BIT);
        /**
         * 生成id機(jī)器標(biāo)識(shí)部分
         */
        private long machineIdPart;
        /**
         * 序列號(hào)
         */
        private long sequence = 0L;
        /**
         * 上一次時(shí)間戳
         */
        private long lastStamp = -1L;

        /**
         * 構(gòu)造函數(shù)初始化機(jī)器編碼
         */
        private SnowFlake() {
            //模擬這里獲得本機(jī)機(jī)器編碼
            long localIp = 4321;
            //localIp & MAX_MACHINE_ID最大不會(huì)超過1023,在左位移12位
            machineIdPart = (localIp & MAX_MACHINE_ID) << SEQUENCE_BIT;
        }
        /**
         * 獲取雪花ID
         */
        public synchronized long nextId() {
            long currentStamp = timeGen();
            //避免機(jī)器時(shí)鐘回?fù)?
            while (currentStamp < lastStamp) {
                // //服務(wù)器時(shí)鐘被調(diào)整了,ID生成器停止服務(wù).
                throw new RuntimeException(String.format("時(shí)鐘已經(jīng)回?fù)?  Refusing to generate id for %d milliseconds", lastStamp - currentStamp));
            }
            if (currentStamp == lastStamp) {
                // 每次+1
                sequence = (sequence + 1) & MAX_SEQUENCE;
                // 毫秒內(nèi)序列溢出
                if (sequence == 0) {
                    // 阻塞到下一個(gè)毫秒,獲得新的時(shí)間戳
                    currentStamp = getNextMill();
                }
            } else {
                //不同毫秒內(nèi)，序列號(hào)置0
                sequence = 0L;
            }
            lastStamp = currentStamp;
            //時(shí)間戳部分+機(jī)器標(biāo)識(shí)部分+序列號(hào)部分
            return (currentStamp - START_TIMESTAMP) << TIMESTAMP_LEFT | machineIdPart | sequence;
        }
        /**
         * 阻塞到下一個(gè)毫秒，直到獲得新的時(shí)間戳
         */
        private long getNextMill() {
            long mill = timeGen();
            //
            while (mill <= lastStamp) {
                mill = timeGen();
            }
            return mill;
        }
        /**
         * 返回以毫秒為單位的當(dāng)前時(shí)間
         */
        protected long timeGen() {
            return System.currentTimeMillis();
        }
    }

    /**
     * 獲取long類型雪花ID
     */
    public static long uniqueLong() {
        return SnowIdUtils.SnowFlake.SNOW_FLAKE.nextId();
    }
    /**
     * 獲取String類型雪花ID
     */
    public static String uniqueLongHex() {
        return String.format("%016x", uniqueLong());
    }

    /**
     * 測(cè)試
     */
    public static void main(String[] args) throws InterruptedException {
        //計(jì)時(shí)開始時(shí)間
        long start = System.currentTimeMillis();
        //讓100個(gè)線程同時(shí)進(jìn)行
        final CountDownLatch latch = new CountDownLatch(100);
        //判斷生成的20萬條記錄是否有重復(fù)記錄
        final Map<Long, Integer> map = new ConcurrentHashMap();
        for (int i = 0; i < 100; i++) {
            //創(chuàng)建100個(gè)線程
            new Thread(() -> {
                for (int s = 0; s < 2000; s++) {
                    long snowID = SnowIdUtils.uniqueLong();
                    log.info("生成雪花ID={}",snowID);
                    Integer put = map.put(snowID, 1);
                    if (put != null) {
                        throw new RuntimeException("主鍵重復(fù)");
                    }
                }
                latch.countDown();
            }).start();
        }
        //讓上面100個(gè)線程執(zhí)行結(jié)束后，在走下面輸出信息
        latch.await();
        log.info("生成20萬條雪花ID總用時(shí)={}", System.currentTimeMillis() - start);
    }
}

public static void main(String[] args) {
    //41位二進(jìn)制最小值
    String minTimeStampStr = "00000000000000000000000000000000000000000";
    //41位二進(jìn)制最大值
    String maxTimeStampStr = "11111111111111111111111111111111111111111";
    //轉(zhuǎn)10進(jìn)制
    long minTimeStamp = new BigInteger(minTimeStampStr, 2).longValue();
    long maxTimeStamp = new BigInteger(maxTimeStampStr, 2).longValue();
    //一年總共多少毫秒
    long oneYearMills = 1L * 1000 * 60 * 60 * 24 * 365;
    //算出最大可以多少年
    System.out.println((maxTimeStamp - minTimeStamp) / oneYearMills);
}