雪花算法源码

package com.pxzf.website.utils;

public class OrderNOUtil {
    
    
    private static long machineId = 0;

    private static long datacenterId = 0;

    /**
     * 单例模式创建学法算法对象
     */
    private enum SnowFlakeSingleton {
    
    
        Singleton;
        private SnowFlake snowFlake;

        SnowFlakeSingleton() {
    
    
            snowFlake = new SnowFlake(datacenterId, machineId);
        }

        public SnowFlake getInstance() {
    
    
            return snowFlake;
        }
    }


    public static long getUUID() {
    
    
        return SnowFlakeSingleton.Singleton.getInstance().nextId();
    }

    public static void main(String[] args) {
    
    
        Thread[] threads = new Thread[10];
        for (int i = 0; i < threads.length; i++) {
    
    
            threads[i]=new Thread(new MyThread());
            threads[i].start();
        }
        flag=true;
    }

    private static volatile boolean flag = false;

    static class MyThread implements Runnable {
    
    

        @Override
        public void run() {
    
    
            while (!flag) {
    
    

            }
            long time=System.currentTimeMillis();
            for (int i = 0; i < 10000; i++) {
    
    
                getUUID();
            }
            System.out.println(System.currentTimeMillis()-time);
        }

    }

}

package com.pxzf.website.utils;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

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
//    private Lock lock=new ReentrantLock(true);
    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();
    }
}

经测试雪花算法中使用synchronized比lock快。