雪花算法和UUID
public class SnowFlake {
// 数据中心(机房) id
private long datacenterId;
// 机器ID
private long workerId;
// 同一时间的序列
private long sequence;
public SnowFlake(long workerId, long datacenterId) {
this(workerId, datacenterId, 0);
}
public SnowFlake(long workerId, long datacenterId, long sequence) {
// 合法判断
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
}
if (datacenterId > maxDatacenterId || datacenterId < 0) {
throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
}
System.out.printf("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d",
timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId);
this.workerId = workerId;
this.datacenterId = datacenterId;
this.sequence = sequence;
}
// 开始时间戳（2021-10-16 22:03:32）
private long twepoch = 1634393012000L;
// 机房号，的ID所占的位数 5个bit 最大:11111(2进制)--> 31(10进制)
private long datacenterIdBits = 5L;
// 机器ID所占的位数 5个bit 最大:11111(2进制)--> 31(10进制)
private long workerIdBits = 5L;
// 5 bit最多只能有31个数字，就是说机器id最多只能是32以内
private long maxWorkerId = -1L ^ (-1L << workerIdBits);
// 5 bit最多只能有31个数字，机房id最多只能是32以内
private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
// 同一时间的序列所占的位数 12个bit 111111111111 = 4095 最多就是同一毫秒生成4096个
private long sequenceBits = 12L;
// workerId的偏移量
private long workerIdShift = sequenceBits;
// datacenterId的偏移量
private long datacenterIdShift = sequenceBits + workerIdBits;
// timestampLeft的偏移量
private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
// 序列号掩码 4095 (0b111111111111=0xfff=4095)
// 用于序号的与运算，保证序号最大值在0-4095之间
private long sequenceMask = -1L ^ (-1L << sequenceBits);
// 最近一次时间戳
private long lastTimestamp = -1L;
// 获取机器ID
public long getWorkerId() {
return workerId;
}
// 获取机房ID
public long getDatacenterId() {
return datacenterId;
}
// 获取最新一次获取的时间戳
public long getLastTimestamp() {
return lastTimestamp;
}
// 获取下一个随机的ID
public synchronized long nextId() {
// 获取当前时间戳，单位毫秒
long timestamp = timeGen();
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));
}
// 去重
if (lastTimestamp == timestamp) {
sequence = (sequence + 1) & sequenceMask;
// sequence序列大于4095
if (sequence == 0) {
// 调用到下一个时间戳的方法
timestamp = tilNextMillis(lastTimestamp);
}
} else {
// 如果是当前时间的第一次获取，那么就置为0
sequence = 0;
}
// 记录上一次的时间戳
lastTimestamp = timestamp;
// 偏移计算
return ((timestamp - twepoch) << timestampLeftShift) |
(datacenterId << datacenterIdShift) |
(workerId << workerIdShift) |
sequence;
}
private long tilNextMillis(long lastTimestamp) {
// 获取最新时间戳
long timestamp = timeGen();
// 如果发现最新的时间戳小于或者等于序列号已经超4095的那个时间戳
while (timestamp <= lastTimestamp) {
// 不符合则继续
timestamp = timeGen();
}
return timestamp;
}
private long timeGen() {
return System.currentTimeMillis();
}
public static void main(String[] args) {
SnowFlake worker = new SnowFlake(1, 1);
long timer = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
worker.nextId();
}
System.out.println(System.currentTimeMillis());
System.out.println(System.currentTimeMillis() - timer);
}
}