Twitter的分布式雪花算法 SnowFlake 每秒自增生成26個萬個可排序的ID

1、twitter的SnowFlake生成ID能夠按照時間有序生成
2捺癞、SnowFlake算法生成id的結(jié)果是一個64bit大小的整數(shù)
3夷蚊、分布式系統(tǒng)內(nèi)不會產(chǎn)生重復id（用有datacenterId和machineId來做區(qū)分）
datacenterId（分布式）（服務ID 1，2髓介，3.....） 每個服務中寫死
machineId（用于集群） 機器ID 讀取機器的環(huán)境變量MACHINEID 部署時每臺服務器ID不一樣

/**
 * Twitter的分布式自增ID雪花算法snowflake
 * @author MENG
 * @create 2018-08-23 10:21
 **/
public class SnowFlake {

    /**
     * 起始的時間戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位數(shù)
     */
    private final static long SEQUENCE_BIT = 12; //序列號占用的位數(shù)
    private final static long MACHINE_BIT = 5;   //機器標識占用的位數(shù)
    private final static long DATACENTER_BIT = 5;//數(shù)據(jù)中心占用的位數(shù)

    /**
     * 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;  //數(shù)據(jù)中心
    private long machineId;     //機器標識
    private long sequence = 0L; //序列號
    private long lastStmp = -1L;//上一次時間戳

    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;
    }

    /**
     * 產(chǎn)生下一個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) {
            //相同毫秒內(nèi)惕鼓，序列號自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列數(shù)已經(jīng)達到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒內(nèi)，序列號置為0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //時間戳部分
                | datacenterId << DATACENTER_LEFT       //數(shù)據(jù)中心部分
                | machineId << MACHINE_LEFT             //機器標識部分
                | sequence;                             //序列號部分
    }

    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(1, 1);

        long start = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            System.out.println(snowFlake.nextId());
        }

        System.out.println(System.currentTimeMillis() - start);


    }
}