序列号生成器

public synchronized String nextId() { long timestamp = timeGen(); //获取当前毫秒数 //如果服务器时间有问题(时钟后退) 报错。 if (timestamp < lastTimestamp) { throw new RuntimeException(String.format( "Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp)); } //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12bit，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4095，当为4096时，与sequenceMask相与，sequence就等于0 if (sequence == 0) { timestamp = tilNextMillis(lastTimestamp); //自旋等待到下一毫秒 } } else { sequence = 0L; //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 } lastTimestamp = timestamp; long suffix = (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence; String datePrefix = DateFormatUtils.format(timestamp, "yyyyMMddHHMMssSSS"); return datePrefix + suffix; } protected long tilNextMillis(long lastTimestamp) { long timestamp = timeGen(); while (timestamp <= lastTimestamp) { timestamp = timeGen(); } return timestamp; } protected long timeGen() { return System.currentTimeMillis(); } private byte getLastIP(){ byte lastip = 0; try{ InetAddress ip = InetAddress.getLocalHost(); byte[] ipByte = ip.getAddress(); lastip = ipByte[ipByte.length - 1]; } catch (UnknownHostException e) { e.printStackTrace(); } return lastip; }