snowflake分析

雪花算法

结构图

1. 共64位
2. 第一位 占位符
3. 之后的41位存储二进制毫秒时间,最大存储到2039年
4. 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
5. 最后12位存储不规则序列号

实现效果

1. 有序 按照时间戳排序,整体有序
2. 唯一 在分布式系统架构中也能达到无碰撞,获取唯一id
3. 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
4. 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.hutoolgroupId>
    <artifactId>hutool-captchaartifactId>
    <version>5.3.6version>
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();
    }
}