魔改後的雪花算法
生成13位long類型ID,适用于單機版,避免平行越權
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public class IdWorker{
//12位的序列号
private static long sequence;
//初始時間戳
private static long twepoch = 1288834974657L;
//序列号id長度
private static long sequenceBits = 4L;
//序列号最大值
private static long sequenceMask = -1L ^ (-1L << sequenceBits);
//時間戳需要左移位數 4位
private static long timestampLeftShift = sequenceBits;
//上次時間戳,初始值為負數
private static long lastTimestamp = -1L;
//下一個ID生成算法
public static synchronized long nextId() {
long timestamp = timeGen();
//擷取目前時間戳如果小于上次時間戳,則表示時間戳擷取出現異常
if (timestamp < lastTimestamp) {
System.err.printf("clock is moving backwards. Rejecting requests until %d.", lastTimestamp);
throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
lastTimestamp - timestamp));
}
//擷取目前時間戳如果等于上次時間戳(同一毫秒内),則在序列号加一;否則序列号指派為0,從0開始。
if (lastTimestamp == timestamp) {
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0;
}
//将上次時間戳值重新整理
lastTimestamp = timestamp;
/**
* 傳回結果:
* (timestamp - twepoch) << timestampLeftShift) 表示将時間戳減去初始時間戳,再左移相應位數
* (datacenterId << datacenterIdShift) 表示将資料id左移相應位數
* (workerId << workerIdShift) 表示将工作id左移相應位數
* | 是按位或運算符,例如:x | y,隻有當x,y都為0的時候結果才為0,其它情況結果都為1。
* 因為個部分隻有相應位上的值有意義,其它位上都是0,是以将各部分的值進行 | 運算就能得到最終拼接好的id
*/
System.out.println("(timestamp - twepoch) :" + (timestamp - twepoch));
System.out.println("front :" + ((timestamp - twepoch) << timestampLeftShift));
System.out.println("sequence :" + sequence);
return ((timestamp - twepoch) << timestampLeftShift) | sequence;
}
//擷取時間戳,并與上次時間戳比較
private static long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}
//擷取系統時間戳
private static long timeGen(){
return System.currentTimeMillis();
}
}