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其实雪花算法比较简单，可能称不上什么算法就是一种构造UID的方法。
点1：UID是一个long类型的41位时间戳，10位存储机器码，12位存储序列号。
点2：时间戳的单位是毫秒，可以同时链接1024台机器，每台机器每毫秒可以使用4096个序列好，我们会给生成id上一个同步锁，阻塞住其他线程的访问。
点3：利用掩码我们可以检测序列是否溢出，如果溢出的话，就强制等待到下一毫秒。

/*** @author hardstone* @since 29 July 2023(1690603385473)*/
public class SnowFlakes {//开始的时间戳private final  long start = 1690603385473L;//机器标识长度5位private final long machineIdBits = 5L;//机器集群标识长度5位private final long centerIdBits = 5L;//序列标识所占位数12位private final long sequenceBits = 12L;//机器标识最大值private final long maxMachineId = -1L ^ (-1L << machineIdBits);//机器集群标识最大值private final long maxCenterId = -1L ^ (-1L << centerIdBits);//序列标识的最大值private final long sequenceMask = -1L ^ (-1L << sequenceBits);//机器标识左移长度private final long machineIdShift = sequenceBits;//机器集群标识左移长度private final long centerIdShift = sequenceBits + machineIdBits;//时间戳左移长度private final long timeStampIdShift = sequenceBits + machineIdBits + centerIdBits;//序列Idprivate long sequence = 0L;//机器Idprivate long machineId;//机器集群Idprivate long centerId;//时间戳private long lastTimeStamp = -1L;public SnowFlakes(long machineId, long centerId) {if (machineId > maxMachineId || machineId < 0) {throw new IllegalArgumentException(String.format("WorkerId should be between 0 and 31"));}if (centerId > maxCenterId || centerId < 0) {throw new IllegalArgumentException(String.format("CenterId should be between 0 and 31"));}}public synchronized long nextId() {long timeStamp = System.currentTimeMillis();//时间回滚现象if (timeStamp < lastTimeStamp) {throw new RuntimeException(String.format("Time gone backwards!"));}if (lastTimeStamp == timeStamp) {sequence = (sequence + 1) & sequenceMask;//如果序列分配完了if (sequence == 0) {timeStamp = getNextMillis(lastTimeStamp);}} else {sequence = 0L;}lastTimeStamp = timeStamp;return ((timeStamp - start) << timeStampIdShift)| (centerId << centerIdShift)| (machineId << machineIdShift)| sequence;}protected long getNextMillis(long lastTimeStamp) {long timeStamp = System.currentTimeMillis();while (timeStamp <= lastTimeStamp) {timeStamp = System.currentTimeMillis();}return timeStamp;}public static void main(String[] args) {System.out.println(new SnowFlakes(0, 0).nextId());}
}