SnowFlakeID

package com.bjtcrj.scm.common.utils;

/**
 * 雪花算法
 * 64位ID = 1位符号位(固定为0,表示正数) + 41位时间戳 + 10位工作机器id + 12位序列号
 *
 * @author shuyan.qi
 * @date 2020/5/3 9:42 下午
 */
public class SnowFlakeID {
    //12位序列号
    private long sequence;//序列号
    private long sequenceBits = 12L;//序列号位数
    private long maxSequence = -1 ^ (-1 << sequenceBits);//序列号最大值

    //10位工作机器id = 5位机房id + 5位机器id
    private long workerId;//机器id
    private long workerIdBits = 5L;//机器id位数
    private long maxWorkerId = -1 ^ (-1 << workerIdBits);//机器id最大值
    private long workerIdMoveBits = sequenceBits;//机器id左移位数 = 序列号位数
    private long workerIdAfterMove = 0L;//左移后的机器id

    private long workerCenterId;//机房id
    private long workerCenterIdBits = 5L;//机房id位数
    private long maxWorkerCenterId = -1 ^ (-1 << workerCenterIdBits);//机房id最大值
    private long workerCenterIdMoveBits = workerIdBits + workerIdMoveBits;//机房id左移位数 = 机器id位数 + 序列号位数
    private long workerCenterIdAfterMove = 0L;//左移后的机房id

    //41位时间戳
    private long lastTimestamp = -1L;//默认-1L
    private long initTimestamp = 1588518046057L;//初始时间戳
    private long timestampMoveBits = workerCenterIdBits + workerCenterIdMoveBits;//时间戳左移位数 = 机房id位数 + 机器id位数 + 序列号位数

    public SnowFlakeID(long workerCenterId, long workerId) {
        if (workerCenterId < 0 || workerCenterId > maxWorkerCenterId) {
            throw new IllegalArgumentException("workerCenterId is illegal");
        }
        if (workerId < 0 || workerId > maxWorkerId) {
            throw new IllegalArgumentException("workerId is illegal");
        }
        this.workerCenterId = workerCenterId;
        this.workerId = workerId;
        this.workerCenterIdAfterMove = this.workerCenterId << this.workerCenterIdMoveBits;
        this.workerIdAfterMove = this.workerCenterId << this.workerCenterIdMoveBits;
    }

    /**
     * 生成ID的核心方法
     */
    public synchronized long nextId() {
        long currentTimestamp = timestamp();
        if (currentTimestamp < lastTimestamp) {
            String s = String.format("currentTimestamp is earlier than lastTimestamp,lastTimestamp=%s,currentTimestamp=%s", lastTimestamp, currentTimestamp);
            System.out.println(s);
            //throw new RuntimeException(s);
            // 时钟回拨后手动拨正。
            // 因为依赖lastTimestamp，所以重启后第一次就发生时钟回拨的情况无法处理。
            // 可以将lastTimestamp存放到redis之类第三方缓存中，但这样生成id的效率会降低，请开发者根据实际情况去选择。
            currentTimestamp = lastTimestamp;
        }
        if (currentTimestamp == lastTimestamp) {
            //同一时间戳，序列号加1
            sequence = (sequence + 1) & maxSequence;
            if (sequence == 0L) {
                //如果序列号加1后的值为0，表示当前时间戳内的序列号已用完，需要获取下一个时间戳
                currentTimestamp = nextTimestamp(currentTimestamp);
            }
        } else {
            sequence = 0L;//不同时间戳，重置序列号
        }
        lastTimestamp = currentTimestamp;//更新成功生成id的最新时间戳
        return ((currentTimestamp - initTimestamp) << timestampMoveBits) | workerCenterIdAfterMove | workerIdAfterMove | sequence;
    }

    /**
     * 获取timestamp的下一毫秒数
     *
     * @param timestamp 当前毫秒数
     * @return
     */
    public long nextTimestamp(long timestamp) {
        long timestamp1 = 0L;
        do {
            timestamp1 = timestamp();
        } while (timestamp >= timestamp1);
        return timestamp1;
    }

    /**
     * 获取当前时间戳
     *
     * @return
     */
    public long timestamp() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) throws InterruptedException {

     /*
        //测试并发
        Map<String,Object> map = new ConcurrentHashMap<>();
        SnowFlakeID snowFlakeID = new SnowFlakeID(1, 1);
        for(int i = 0;i < 100;i++){
            new Thread(() -> {
                try {
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                for (int j = 0 ;j < 100000;j++){
                    map.put(String.valueOf(snowFlakeID.nextId()),1);
                }
            }).start();;
        }

        for(;;){
            TimeUnit.SECONDS.sleep(1);
            System.out.println("size="+map.size());
        }

    */
        //测试速度
        long startTime = System.currentTimeMillis();
        for (int i = 0; i < 30; i++) {
            System.out.println(getId());
        }
        System.out.println("耗时：" + (System.currentTimeMillis() - startTime) / 1000.0d + "秒");
    }

    private static SnowFlakeID snowFlakeID = new SnowFlakeID(1, 1);
    public static long getId() {
        return snowFlakeID.nextId();
    }
}