自增主键之雪花算法

古城微笑少年丶 2021-09-23 10:14 411阅读 0赞

package com.qcloud.component.goods.web.controller.outside;
    
    /**
     * Twitter的分布式自增ID雪花算法snowflake
     **/
    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(1, 1);
    
            long start = System.currentTimeMillis();
            for (int i = 0; i < 1000000; i++) {
                System.out.println(snowFlake.nextId());
            }
    
            System.out.println(System.currentTimeMillis() - start);
    
    
        }
    }