结构图
- 共64位
- 第一位 占位符
- 之后的41位存储二进制毫秒时间,最大存储到2039年
- 后十位 5位存储机房id,5位存储机器id,一共10位最多存储1024个节点的机房机器码
- 最后12位存储不规则序列号
实现效果
- 有序 按照时间戳排序,整体有序
- 唯一 在分布式系统架构中也能达到无碰撞,获取唯一id
- 无规则 因为后12位是无规则,就无法通过序列号获取当前系统的数据
- 长度为19位,易于存储 例如uuid为32位,加上-共36位 太长不容易存储
缺陷
此时生成的id的时间是本地时间,如果本地时钟回调,还是有可能出现重复
解决办法:
百度的UidGenerator
美团的Leaf
java源码实现
twitter的雪花算法是scala语言的
/**
* twitter的snowflake算法 -- java实现
*
* @author beyond
* @date 2016/11/26
*/
public class SnowFlake {
/**
* 起始的时间戳
*/
private final static long START_STMP = 1480166465631L;
/**
* 每一部分占用的位数
*/
private final static long SEQUENCE_BIT = 12; //序列号占用的位数
private final static long MACHINE_BIT = 5; //机器标识占用的位数
private final static long DATACENTER_BIT = 5;//数据中心占用的位数
/**
* 每一部分的最大值
*/
private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
/**
* 每一部分向左的位移
*/
private final static long MACHINE_LEFT = SEQUENCE_BIT;
private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
private long datacenterId; //数据中心
private long machineId; //机器标识
private long sequence = 0L; //序列号
private long lastStmp = -1L;//上一次时间戳
public SnowFlake(long datacenterId, long machineId) {
if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
}
if (machineId > MAX_MACHINE_NUM || machineId < 0) {
throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
}
this.datacenterId = datacenterId;
this.machineId = machineId;
}
/**
* 产生下一个ID
*
* @return
*/
public synchronized long nextId() {
long currStmp = getNewstmp();
if (currStmp < lastStmp) {
throw new RuntimeException("Clock moved backwards. Refusing to generate id");
}
if (currStmp == lastStmp) {
//相同毫秒内，序列号自增
sequence = (sequence + 1) & MAX_SEQUENCE;
//同一毫秒的序列数已经达到最大
if (sequence == 0L) {
currStmp = getNextMill();
}
} else {
//不同毫秒内，序列号置为0
sequence = 0L;
}
lastStmp = currStmp;
return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
| datacenterId << DATACENTER_LEFT //数据中心部分
| machineId << MACHINE_LEFT //机器标识部分
| sequence; //序列号部分
}
private long getNextMill() {
long mill = getNewstmp();
while (mill <= lastStmp) {
mill = getNewstmp();
}
return mill;
}
private long getNewstmp() {
return System.currentTimeMillis();
}
public static void main(String[] args) {
SnowFlake snowFlake = new SnowFlake(2, 3);
for (int i = 0; i < (1 << 12); i++) {
System.out.println(snowFlake.nextId());
}
}
}
hutool提供工具类级封装
<dependency>
<groupId>cn.hutool</groupId>
<artifactId>hutool-captcha</artifactId>
<version>5.3.6</version>
</dependency>
package com.zhangyao.snowflake.util;
import cn.hutool.core.lang.Snowflake;
import cn.hutool.core.net.NetUtil;
import cn.hutool.core.util.IdUtil;
import cn.hutool.core.util.IdcardUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;
/**
* @author: zhangyao
* @create:2020-06-04 09:23
**/
@Slf4j
@Component
public class SnowflakeUtil {
private long workerId;
@Value("${datacenterId}")
private long datacenterId;
private Snowflake snowflake = IdUtil.createSnowflake(workerId, datacenterId);
@PostConstruct
private void init(){
try{
workerId = NetUtil.ipv4ToLong(NetUtil.getLocalhostStr());
log.info("当前机器id为:{}",workerId);
}catch (Exception e){
e.printStackTrace();
log.warn(e.toString());
workerId = NetUtil.getLocalhost().hashCode();
}
}
public synchronized long getSnowflakeId(){
return snowflake.nextId();
}
public synchronized long getSnowflake(long workerId,long datacenterId){
Snowflake snowflake = new Snowflake(workerId, datacenterId);
return snowflake.nextId();
}
}
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