Java唯一Id生成器基于雪花算法
java代碼
package cn.pconline.common.utils;
import lombok.extern.slf4j.Slf4j;
@Slf4j
public class SnowFlakeUtil {
private static SnowFlakeUtil flowIdWorker = new SnowFlakeUtil(1);
private final long id;
private final long epoch = 1524291141010L;
private final long workerIdBits = 10L;
private final long maxWorkerId = -1L ^ -1L << this.workerIdBits;
private final long sequenceBits = 12L;
private final long workerIdShift = this.sequenceBits;
private final long timestampLeftShift = this.sequenceBits + this.workerIdBits;
private final long sequenceMask = -1L ^ -1L << this.sequenceBits;
private long sequence = 0L;
private long lastTimestamp = -1L;
private SnowFlakeUtil(long id) {
if (id > this.maxWorkerId || id < 0) {
throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", this.maxWorkerId));
}
this.id = id;
}
public static SnowFlakeUtil getFlowIdInstance() {
return flowIdWorker;
}
private static long timeGen() {
return System.currentTimeMillis();
}
public static void main(String[] args) {
for (int i = 0; i < 100; i++) {
SnowFlakeUtil snowFlakeUtil = SnowFlakeUtil.getFlowIdInstance();
System.out.println(snowFlakeUtil.nextId());
}
}
public synchronized long nextId() {
long timestamp = timeGen();
if (this.lastTimestamp == timestamp) {
//如果上一個timestamp與新産生的相等，則sequence加一(0-4095循環); 對新的timestamp，sequence從0開始
this.sequence = this.sequence + 1 & this.sequenceMask;
if (this.sequence == 0) {
// 重新生成timestamp
timestamp = this.tilNextMillis(this.lastTimestamp);
}
} else {
this.sequence = 0;
}
if (timestamp < this.lastTimestamp) {
log.error(String.format("clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
return -1;
}
this.lastTimestamp = timestamp;
return timestamp - this.epoch << this.timestampLeftShift | this.id << this.workerIdShift | this.sequence;
}
private long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}
}