public class SnowFlakeIdWorker {

    /**
     * 開始時(shí)間戳，單位毫秒；這里是2021-06-01
     */
    private static final long TW_EPOCH = 1622476800000L;

    /**
     * 機(jī)器 ID 所占的位數(shù)
     */
    private static final long WORKER_ID_BITS = 5L;

    /**
     * 數(shù)據(jù)標(biāo)識 ID 所占的位數(shù)
     */
    private static final long DATA_CENTER_ID_BITS = 5L;

    /**
     * 支持的最大機(jī)器ID，最大為31
     *
     * PS. Twitter的源碼是 -1L ^ (-1L << workerIdBits)；這里最后和-1進(jìn)行異或運(yùn)算，由于-1的二進(jìn)制補(bǔ)碼的特殊性，就相當(dāng)于進(jìn)行取反。
     */
    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);

    /**
     * 支持的最大機(jī)房ID，最大為31
     */
    private static final long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS);

    /**
     * 序列在 ID 中占的位數(shù)
     */
    private static final long SEQUENCE_BITS = 12L;

    /**
     * 機(jī)器 ID 向左移12位
     */
    private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;

    /**
     * 機(jī)房 ID 向左移17位
     */
    private static final long DATA_CENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;

    /**
     * 時(shí)間截向左移22位
     */
    private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATA_CENTER_ID_BITS;

    /**
     * 生成序列的掩碼最大值，最大為4095
     */
    private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);

    /**
     * 工作機(jī)器 ID(0~31)
     */
    private final long workerId;

    /**
     * 機(jī)房 ID(0~31)
     */
    private final long dataCenterId;

    /**
     * 毫秒內(nèi)序列(0~4095)
     */
    private long sequence = 0L;

    /**
     * 上次生成 ID 的時(shí)間戳
     */
    private long lastTimestamp = -1L;

    /**
     * 創(chuàng)建 ID 生成器的方式一: 使用工作機(jī)器的序號(也就是將機(jī)房的去掉給機(jī)器ID使用)，范圍是 [0, 1023]，優(yōu)點(diǎn)是方便給機(jī)器編號
     *
     * @param workerId 工作機(jī)器 ID
     */
    public SnowFlakeIdWorker(long workerId) {
        // 計(jì)算最大值
        long maxMachineId = (MAX_DATA_CENTER_ID + 1) * (MAX_WORKER_ID + 1) - 1;

        if (workerId < 0 || workerId > maxMachineId) {
            throw new IllegalArgumentException(String.format("Worker ID can't be greater than %d or less than 0", maxMachineId));
        }

        // 取高位部分作為機(jī)房ID部分
        this.dataCenterId = (workerId >> WORKER_ID_BITS) & MAX_DATA_CENTER_ID;
        // 取低位部分作為機(jī)器ID部分
        this.workerId = workerId & MAX_WORKER_ID;
    }

    /**
     * 創(chuàng)建 ID 生成器的方式二: 使用工作機(jī)器 ID 和機(jī)房 ID，優(yōu)點(diǎn)是方便分機(jī)房管理
     *
     * @param dataCenterId 機(jī)房 ID (0~31)
     * @param workerId     工作機(jī)器 ID (0~31)
     */
    public SnowFlakeIdWorker(long dataCenterId, long workerId) {
        if (workerId > MAX_WORKER_ID || workerId < 0) {
            throw new IllegalArgumentException(String.format("Worker ID can't be greater than %d or less than 0", MAX_WORKER_ID));
        }
        if (dataCenterId > MAX_DATA_CENTER_ID || dataCenterId < 0) {
            throw new IllegalArgumentException(String.format("DataCenter ID can't be greater than %d or less than 0", MAX_DATA_CENTER_ID));
        }

        this.workerId = workerId;
        this.dataCenterId = dataCenterId;
    }

    /**
     * 獲得下一個(gè) ID(該方法是線程安全的)
     *
     * @return 返回一個(gè)長度位15的 long類型的數(shù)字
     */
    public synchronized long nextId() {
        long timestamp = timeGen();
        // 如果當(dāng)前時(shí)間小于上一次 ID 生成的時(shí)間戳，說明發(fā)生時(shí)鐘回?fù)?，為保證ID不重復(fù)拋出異常。
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        if (lastTimestamp == timestamp) {
            // 同一時(shí)間生成的，則序號+1
            sequence = (sequence + 1) & SEQUENCE_MASK;
            // 毫秒內(nèi)序列溢出：超過最大值
            if (sequence == 0) {
                // 阻塞到下一個(gè)毫秒，獲得新的時(shí)間戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 時(shí)間戳改變，毫秒內(nèi)序列重置
            sequence = 0L;
        }
        // 上次生成 ID 的時(shí)間戳
        lastTimestamp = timestamp;

        // 移位并通過或運(yùn)算拼到一起
        return ((timestamp - TW_EPOCH) << TIMESTAMP_LEFT_SHIFT)
                | (dataCenterId << DATA_CENTER_ID_SHIFT)
                | (workerId << WORKER_ID_SHIFT)
                | sequence;
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }
}

// 初始化
SnowFlakeIdWorker idWorker = new SnowFlakeIdWorker(1, 0);

// 生成ID
for(int i=0; i<100; i++){
    System.out.println(idWorker.nextId());
}