com.xiaoleilu.hutool.lang.Snowflake Maven / Gradle / Ivy
package com.xiaoleilu.hutool.lang;
import com.xiaoleilu.hutool.date.SystemClock;
/**
* Twitter的Snowflake 算法
* 分布式系统中，有一些需要使用全局唯一ID的场景，有些时候我们希望能使用一种简单一些的ID，并且希望ID能够按照时间有序生成。
* snowflake的结构如下(每部分用-分开):
*
*
* 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000
*
*
* 第一位为未使用，接下来的41位为毫秒级时间(41位的长度可以使用69年)
* 然后是5位datacenterId和5位workerId(10位的长度最多支持部署1024个节点）
* 最后12位是毫秒内的计数（12位的计数顺序号支持每个节点每毫秒产生4096个ID序号）
*
* 参考：http://www.cnblogs.com/relucent/p/4955340.html
*
* @author Looly
* @since 3.0.1
*/
public class Snowflake {
private final long twepoch = 1288834974657L;
private final long workerIdBits = 5L;
private final long datacenterIdBits = 5L;
private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
private final long sequenceBits = 12L;
private final long workerIdShift = sequenceBits;
private final long datacenterIdShift = sequenceBits + workerIdBits;
private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
private final long sequenceMask = -1L ^ (-1L << sequenceBits);
private long workerId;
private long datacenterId;
private long sequence = 0L;
private long lastTimestamp = -1L;
private boolean useSystemClock;
/**
* 构造
* @param workerId 终端ID
* @param datacenterId 数据中心ID
*/
public Snowflake(long workerId, long datacenterId) {
this(workerId, datacenterId, false);
}
/**
* 构造
* @param workerId 终端ID
* @param datacenterId 数据中心ID
* @param isUseSystemClock 是否使用{@link SystemClock} 获取当前时间戳
*/
public Snowflake(long workerId, long datacenterId, boolean isUseSystemClock) {
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));
}
this.workerId = workerId;
this.datacenterId = datacenterId;
this.useSystemClock = isUseSystemClock;
}
/**
* 下一个ID
* @return ID
*/
public synchronized long nextId() {
long timestamp = useSystemClock ? SystemClock.now() : System.currentTimeMillis();
if (timestamp < lastTimestamp) {
throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
}
if (lastTimestamp == timestamp) {
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}
lastTimestamp = timestamp;
return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
}
private long tilNextMillis(long lastTimestamp) {
long timestamp = useSystemClock ? SystemClock.now() : System.currentTimeMillis();
while (timestamp <= lastTimestamp) {
timestamp = useSystemClock ? SystemClock.now() : System.currentTimeMillis();
}
return timestamp;
}
}