雪花算法生成唯一ID

灰太狼 2022-12-27 01:13 217阅读 0赞

/**
     * @author ws
     * @description: 雪花算法生成唯一ID
     * @datetime 2020/6/26 10:07
     */
    public class SnowFlake {
        public static void main(String[] args) {
            System.out.println(getId());
        }
        /**
         * 起始的时间戳(2020-05-27 00:00:00)
         */
        private final static long START_STAMP = 1590508800000L;
    
        /**
         * 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 DATA_CENTER_BIT = 5;//数据中心占用的位数
    
        /**
         * 每一部分的最大值
         */
        private final static long MAX_DATA_CENTER_NUM = -1L ^ (-1L << DATA_CENTER_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 DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
        private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;
    
        //单例模式
        private static SnowFlake snowFlake;
    
        static {
            snowFlake = new SnowFlake(1,2);
        }
    
    
        public static long getId(){
            return snowFlake.nextId();
        }
    
        private long dataCenterId;  //数据中心
        private long machineId;     //机器标识
        private long sequence = 0L; //序列号
        private long lastStamp = -1L;//上一次时间戳
    
        private SnowFlake(long dataCenterId, long machineId) {
            if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {
                throw new IllegalArgumentException("dataCenterId can't be greater than MAX_DATA_CENTER_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 currStamp = getNewStamp();
            if (currStamp < lastStamp) {
                throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
            }
    
            if (currStamp == lastStamp) {
                //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) {
                    currStamp = getNextMill();
                }
            } else {
                //不同毫秒内，序列号置为0
                sequence = 0L;
            }
    
            lastStamp = currStamp;
    
            return (currStamp - START_STAMP) << TIMESTAMP_LEFT //时间戳部分
                    | dataCenterId << DATA_CENTER_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 = getNewStamp();
            while (mill <= lastStamp) {
                mill = getNewStamp();
            }
            return mill;
        }
    
        private long getNewStamp() {
            return System.currentTimeMillis();
        }
    
    }