/**
* 自定义 ID 生成器
* ID 生成规则: ID长达 64 bits
*
* | 41 bits: Timestamp (毫秒) | 3 bits: 区域（机房） | 10 bits: 机器编号 | 10 bits: 序列号 |
*/
public class GameUUID{
// 基准时间
private long twepoch = 1288834974657L; //Thu, 04 Nov 2010 01:42:54 GMT
// 区域标志位数
private final static long regionIdBits = 3L;
// 机器标识位数
private final static long workerIdBits = 10L;
// 序列号识位数
private final static long sequenceBits = 10L;
// 区域标志ID最大值
private final static long maxRegionId = -1L ^ (-1L << regionIdBits);
// 机器ID最大值
private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
// 序列号ID最大值
private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
// 机器ID偏左移10位
private final static long workerIdShift = sequenceBits;
// 业务ID偏左移20位
private final static long regionIdShift = sequenceBits + workerIdBits;
// 时间毫秒左移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) {
// 如果超出范围就抛出异常
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) {
// 如果超出范围就抛出异常
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);
}
/**
* 实际产生代码的
*
* @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();
}
}
//如果上次生成时间和当前时间相同,在同一毫秒内
if (lastTimestamp == timestamp) {
//sequence自增，因为sequence只有10bit，所以和sequenceMask相与一下，去掉高位
sequence = (sequence + 1) & sequenceMask;
//判断是否溢出,也就是每毫秒内超过1024，当为1024时，与sequenceMask相与，sequence就等于0
if (sequence == 0) {
//自旋等待到下一毫秒
timestamp = tailNextMillis(lastTimestamp);
}
} else {
// 如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加,
// 为了保证尾数随机性更大一些,最后一位设置一个随机数
sequence = new SecureRandom().nextInt(10);
}
lastTimestamp = timestamp;
return ((timestamp - twepoch) << timestampLeftShift) | (paddingnum << regionIdShift) | (workerId << workerIdShift) | sequence;
}
// 防止产生的时间比之前的时间还要小（由于NTP回拨等问题）,保持增量的趋势.
private long tailNextMillis(final long lastTimestamp) {
long timestamp = this.timeGen();
while (timestamp <= lastTimestamp) {
timestamp = this.timeGen();
}
return timestamp;
}
// 获取当前的时间戳
protected long timeGen() {
return System.currentTimeMillis();
}
}