雪花算法代码及其用法

1 简介：

雪花算法是推特内部使用的分布式环境下的唯一ID生成算法，它基于时间戳生成，保证有序递增，加以入计算机硬件等元素，可以满足高并发环境下ID不重复。

2 代码：把下面代码放到工具类中

package com.xuecheng.base.utils;

import java.util.Random;

/**
 * snow flow .
 *
 */
public final class IdWorkerUtils {

    private static final Random RANDOM = new Random();

    private static final long WORKER_ID_BITS = 5L;

    private static final long DATACENTERIDBITS = 5L;

    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);

    private static final long MAX_DATACENTER_ID = ~(-1L << DATACENTERIDBITS);

    private static final long SEQUENCE_BITS = 12L;

    private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;

    private static final long DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;

    private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTERIDBITS;

    private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);

    private static final IdWorkerUtils ID_WORKER_UTILS = new IdWorkerUtils();

    private long workerId;

    private long datacenterId;

    private long idepoch;

    private long sequence = '0';

    private long lastTimestamp = -1L;

    private IdWorkerUtils() {
       this(RANDOM.nextInt((int) MAX_WORKER_ID), RANDOM.nextInt((int) MAX_DATACENTER_ID), 1288834974657L);
    }

    private IdWorkerUtils(final long workerId, final long datacenterId, final long idepoch) {
       if (workerId > MAX_WORKER_ID || workerId < 0) {
          throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", MAX_WORKER_ID));
       }
       if (datacenterId > MAX_DATACENTER_ID || datacenterId < 0) {
          throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", MAX_DATACENTER_ID));
       }
       this.workerId = workerId;
       this.datacenterId = datacenterId;
       this.idepoch = idepoch;
    }

    /**
     * Gets instance.
     *
     * @return the instance
     */
    public static IdWorkerUtils getInstance() {
       return ID_WORKER_UTILS;
    }

    public synchronized long nextId() {
       long timestamp = timeGen();
       if (timestamp < lastTimestamp) {
          throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
       }
       if (lastTimestamp == timestamp) {
          sequence = (sequence + 1) & SEQUENCE_MASK;
          if (sequence == 0) {
             timestamp = tilNextMillis(lastTimestamp);
          }
       } else {
          sequence = 0L;
       }

       lastTimestamp = timestamp;

       return ((timestamp - idepoch) << TIMESTAMP_LEFT_SHIFT)
             | (datacenterId << DATACENTER_ID_SHIFT)
             | (workerId << WORKER_ID_SHIFT) | sequence;
    }

    private long tilNextMillis(final long lastTimestamp) {
       long timestamp = timeGen();
       while (timestamp <= lastTimestamp) {
          timestamp = timeGen();
       }
       return timestamp;
    }

    private long timeGen() {
       return System.currentTimeMillis();
    }

    /**
     * Build part number string.
     *
     * @return the string
     */
    public String buildPartNumber() {
       return String.valueOf(ID_WORKER_UTILS.nextId());
    }

    /**
     * Create uuid string.
     *
     * @return the string
     */
    public String createUUID() {
       return String.valueOf(ID_WORKER_UTILS.nextId());
    }

    public static void main(String[] args) {
       System.out.println(IdWorkerUtils.getInstance().nextId());
    }
}

3 用法，比如生成一个随机号