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SnowFlake 雪花算法生成id

雪花算法生成的id 是一个long类型的  转换成二进制 是64位  

0   |      00000000000000000000000000000000000000000  |   0000000000|    000000000000
 

第一部分:第一位0 表示符号位   因为生成的id都是正数  所以第一位就是0  (用第一位标识正负 1表示负数 0表示正数)

第二部分:00000000000000000000000000000000000000000  这个41位表示当前服务器的时间戳 毫秒值  因为毫秒值转换成二进制 就是41位    时间戳的最大值  是大约70年  

第三部分:  0000000000  这10位中 前五位标识 机器id  后五位表示 集群id   也就是说机器id 最大值是2的5次方减1 也就是31  集群id最大值也是31

第四部分:000000000000 这12位表示 序列    12位都是1 最多是 4095   也就是说 每台机器 每毫秒最多能生成4095个id

代码示例

package com.xiao;


public class IdWorker{

    //下面两个每个5位,加起来就是10位的工作机器id
    private long workerId;    //工作id
    private long datacenterId;   //数据id
    //12位的序列号
    private long sequence;

    public IdWorker(long workerId, long datacenterId, long sequence){
        // sanity check for workerId
        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;
    }

    //初始时间戳
    private long twepoch = 1288834974657L;

    //长度为5位
    private long workerIdBits = 5L;
    private long datacenterIdBits = 5L;
    //最大值
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    //序列号id长度
    private long sequenceBits = 12L;
    //序列号最大值
    private long sequenceMask = -1L ^ (-1L << sequenceBits);
    
    //工作id需要左移的位数,12位
    private long workerIdShift = sequenceBits;
   //数据id需要左移位数 12+5=17位
    private long datacenterIdShift = sequenceBits + workerIdBits;
    //时间戳需要左移位数 12+5+5=22位
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    
    //上次时间戳,初始值为负数
    private long lastTimestamp = -1L;

    public long getWorkerId(){
        return workerId;
    }

    public long getDatacenterId(){
        return datacenterId;
    }

    public long getTimestamp(){
        return System.currentTimeMillis();
    }

     //下一个ID生成算法
    public synchronized long nextId() {
        long timestamp = timeGen();

        //获取当前时间戳如果小于上次时间戳,则表示时间戳获取出现异常
        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));
        }

        //获取当前时间戳如果等于上次时间戳
        //说明:还处在同一毫秒内,则在序列号加1;否则序列号赋值为0,从0开始。
        if (lastTimestamp == timestamp) {  // 0  - 4095
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0;
        }
        
        //将上次时间戳值刷新
        lastTimestamp = timestamp;

        /**
          * 返回结果:
          * (timestamp - twepoch) << timestampLeftShift) 表示将时间戳减去初始时间戳,再左移相应位数
          * (datacenterId << datacenterIdShift) 表示将数据id左移相应位数
          * (workerId << workerIdShift) 表示将工作id左移相应位数
          * | 是按位或运算符,例如:x | y,只有当x,y都为0的时候结果才为0,其它情况结果都为1。
          * 因为个部分只有相应位上的值有意义,其它位上都是0,所以将各部分的值进行 | 运算就能得到最终拼接好的id
        */
        return ((timestamp - twepoch) << timestampLeftShift) |
                (datacenterId << datacenterIdShift) |
                (workerId << workerIdShift) |
                sequence;
    }

    //获取时间戳,并与上次时间戳比较
    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    //获取系统时间戳
    private long timeGen(){
        return System.currentTimeMillis();
    }




    public static void main(String[] args) {
        IdWorker worker = new IdWorker(31,31,0);
        for (int i = 0; i < 100; i++) {
            System.out.println(worker.nextId());
        }
    }

}

 

版权声明
本文为[xiaozhou18]所创,转载请带上原文链接,感谢
https://my.oschina.net/xiaozhou18/blog/4840265

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