mybatis-plus雪花算法自动生成机器id原理及源码

public Sequence() {
    //通过当前物理网卡地址获取datacenterId
    this.datacenterId = getDatacenterId(maxDatacenterId);
    //物理网卡地址+jvm进程pi获取workerId
    this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
}

/**
 * 有参构造器
 *
 * @param workerId     工作机器 ID
 * @param datacenterId 序列号
 */
public Sequence(long workerId, long datacenterId) {
    Assert.isFalse(workerId > maxWorkerId || workerId < 0,
            String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
    Assert.isFalse(datacenterId > maxDatacenterId || datacenterId < 0,
            String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
    this.workerId = workerId;
    this.datacenterId = datacenterId;
}

protected static long getDatacenterId(long maxDatacenterId) {
    long id = 0L;
    try {
        //获取本机(或者服务器ip地址)
        //DESKTOP-123SDAD/192.168.1.87
        InetAddress ip = InetAddress.getLocalHost();
        NetworkInterface network = NetworkInterface.getByInetAddress(ip);
        //一般不是null会进入else
        if (network == null) {
            id = 1L;
        } else {
            //获取物理网卡地址
            byte[] mac = network.getHardwareAddress();
            if (null != mac) {
                id = ((0x000000FF & (long) mac[mac.length - 2]) | (0x0000FF00 & (((long) mac[mac.length - 1]) << 8))) >> 6;
                id = id % (maxDatacenterId + 1);
            }
        }
    } catch (Exception e) {
        logger.warn(" getDatacenterId: " + e.getMessage());
    }
    return id;
}

/**
 * 获取 maxWorkerId
 */
protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
    StringBuilder mpid = new StringBuilder();
    mpid.append(datacenterId);
    //获取jvm进程信息
    String name = ManagementFactory.getRuntimeMXBean().getName();
    if (StringUtils.isNotBlank(name)) {
        /*
         * 获取进程PID
         */
        mpid.append(name.split(StringPool.AT)[0]);
    }
    /*
     * MAC + PID 的 hashcode 获取16个低位
     */
    return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
}