/**
* 自定義 ID 生成器
* ID 生成規(guī)則: ID長達 64 bits
*
* | 41 bits: Timestamp (毫秒) | 3 bits: 區(qū)域（機房） | 10 bits: 機器編號 | 10 bits: 序列號 |
*/
public class GameUUID{
// 基準(zhǔn)時間
private long twepoch = 1288834974657L; //Thu, 04 Nov 2010 01:42:54 GMT
// 區(qū)域標(biāo)志位數(shù)
private final static long regionIdBits = 3L;
// 機器標(biāo)識位數(shù)
private final static long workerIdBits = 10L;
// 序列號識位數(shù)
private final static long sequenceBits = 10L;
// 區(qū)域標(biāo)志ID最大值
private final static long maxRegionId = -1L ^ (-1L << regionIdBits);
// 機器ID最大值
private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
// 序列號ID最大值
private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
// 機器ID偏左移10位
private final static long workerIdShift = sequenceBits;
// 業(yè)務(wù)ID偏左移20位
private final static long regionIdShift = sequenceBits + workerIdBits;
// 時間毫秒左移23位
private final static long timestampLeftShift = sequenceBits + workerIdBits + regionIdBits;
private static long lastTimestamp = -1L;
private long sequence = 0L;
private final long workerId;
private final long regionId;
public GameUUID(long workerId, long regionId) {
// 如果超出范圍就拋出異常
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException("worker Id can't be greater than %d or less than 0");
}
if (regionId > maxRegionId || regionId < 0) {
throw new IllegalArgumentException("datacenter Id can't be greater than %d or less than 0");
}
this.workerId = workerId;
this.regionId = regionId;
}
public GameUUID(long workerId) {
// 如果超出范圍就拋出異常
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException("worker Id can't be greater than %d or less than 0");
}
this.workerId = workerId;
this.regionId = 0;
}
public long generate() {
return this.nextId(false, 0);
}
/**
* 實際產(chǎn)生代碼的
*
* @param isPadding
* @param busId
* @return
*/
private synchronized long nextId(boolean isPadding, long busId) {
long timestamp = timeGen();
long paddingnum = regionId;
if (isPadding) {
paddingnum = busId;
}
if (timestamp < lastTimestamp) {
try {
throw new Exception("Clock moved backwards. Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds");
} catch (Exception e) {
e.printStackTrace();
}
}
//如果上次生成時間和當(dāng)前時間相同,在同一毫秒內(nèi)
if (lastTimestamp == timestamp) {
//sequence自增，因為sequence只有10bit，所以和sequenceMask相與一下，去掉高位
sequence = (sequence + 1) & sequenceMask;
//判斷是否溢出,也就是每毫秒內(nèi)超過1024，當(dāng)為1024時，與sequenceMask相與，sequence就等于0
if (sequence == 0) {
//自旋等待到下一毫秒
timestamp = tailNextMillis(lastTimestamp);
}
} else {
// 如果和上次生成時間不同,重置sequence，就是下一毫秒開始，sequence計數(shù)重新從0開始累加,
// 為了保證尾數(shù)隨機性更大一些,最后一位設(shè)置一個隨機數(shù)
sequence = new SecureRandom().nextInt(10);
}
lastTimestamp = timestamp;
return ((timestamp - twepoch) << timestampLeftShift) | (paddingnum << regionIdShift) | (workerId << workerIdShift) | sequence;
}
// 防止產(chǎn)生的時間比之前的時間還要小（由于NTP回撥等問題）,保持增量的趨勢.
private long tailNextMillis(final long lastTimestamp) {
long timestamp = this.timeGen();
while (timestamp <= lastTimestamp) {
timestamp = this.timeGen();
}
return timestamp;
}
// 獲取當(dāng)前的時間戳
protected long timeGen() {
return System.currentTimeMillis();
}
}