public class SnowflakeIdWorker{
    /** 開始時(shí)間截 (2015-01-01) */
    private final long twepoch = 1288834974657L;
 
    /** 機(jī)器id所占的位數(shù) */
    private final long workerIdBits = 5L;
 
    /** 數(shù)據(jù)標(biāo)識(shí)id所占的位數(shù) */
    private final long datacenterIdBits = 5L;
 
    /** 支持的最大機(jī)器id，結(jié)果是31 (這個(gè)移位算法可以很快的計(jì)算出幾位二進(jìn)制數(shù)所能表示的最大十進(jìn)制數(shù)) */
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
 
    /** 支持的最大數(shù)據(jù)標(biāo)識(shí)id，結(jié)果是31 */
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
 
    /** 序列在id中占的位數(shù) */
    private final long sequenceBits = 12L;
 
    /** 機(jī)器ID向左移12位 */
    private final long workerIdShift = sequenceBits;
 
    /** 數(shù)據(jù)標(biāo)識(shí)id向左移17位(12+5) */
    private final long datacenterIdShift = sequenceBits + workerIdBits;
 
    /** 時(shí)間截向左移22位(5+5+12) */
    private final long timestampLeftShift = sequenceBits + workerIdBits
            + datacenterIdBits;
 
    /** 生成序列的掩碼，這里為4095 (0b111111111111=0xfff=4095) */
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);
 
    /** 工作機(jī)器ID(0~31) */
    private long workerId;
 
    /** 數(shù)據(jù)中心ID(0~31) */
    private long datacenterId;
 
    /** 毫秒內(nèi)序列(0~4095) */
    private long sequence = 0L;
 
    /** 上次生成ID的時(shí)間截 */
    private long lastTimestamp = -1L;
 
    /**
     * 構(gòu)造函數(shù)
     *
     * @param workerId
     *            工作ID (0~31)
     * @param datacenterId
     *            數(shù)據(jù)中心ID (0~31)
     */
    public SnowflakeIdWorker(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format(
                    "worker Id can't be greater than %d or less than 0",
                    maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format(
                    "datacenter Id can't be greater than %d or less than 0",
                    maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }
 
    /**
     * 獲得下一個(gè)ID (該方法是線程安全的)
     *
     * @return SnowflakeId
     */
    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(shuō)明系統(tǒng)時(shí)鐘回退過(guò)這個(gè)時(shí)候應(yīng)當(dāng)拋出異常
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(
                    String.format(
                            "Clock moved backwards.  Refusing to generate id for %d milliseconds",
                            (lastTimestamp - timestamp)));
        }
 
        // 如果是同一時(shí)間生成的，則進(jìn)行毫秒內(nèi)序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            // 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
                timestamp = tilNextMillis(lastTimestamp);
            }
        }
        // 時(shí)間戳改變，毫秒內(nèi)序列重置
        else {
            sequence = 0L;
        }
 
        // 上次生成ID的時(shí)間截
        lastTimestamp = timestamp;
 
        // 移位并通過(guò)或運(yùn)算拼到一起組成64位的ID
        return ((timestamp - twepoch) << timestampLeftShift) //
                | (datacenterId << datacenterIdShift) //
                | (workerId << workerIdShift) //
                | sequence;
    }
 
    /**
     * 阻塞到下一個(gè)毫秒，直到獲得新的時(shí)間戳
     *
     * @param lastTimestamp
     *            上次生成ID的時(shí)間截
     * @return 當(dāng)前時(shí)間戳
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }
 
    /**
     * 返回以毫秒為單位的當(dāng)前時(shí)間
     *
     * @return 當(dāng)前時(shí)間(毫秒)
     */
    protected long timeGen() {
        return System.currentTimeMillis();
    }
 
    //測(cè)試方法
    public static void main(String[] args) {
 
        // 假設(shè)我們有一個(gè)工作機(jī)器ID為1，數(shù)據(jù)中心ID為1的環(huán)境
        long workerId = 1L;
        long datacenterId = 1L;
        
        // 創(chuàng)建一個(gè)SnowflakeIdWorker實(shí)例
        SnowflakeIdWorker idWorker = new SnowflakeIdWorker(workerId, datacenterId);
        
        // 生成并打印10個(gè)ID作為示例
        for (int i = 0; i < 10; i++) {
            long id = idWorker.nextId();
            System.out.println(id);
        }
    }
 
}