111

  1 package com.xiaozhou.springbootwiki.util;
  2 
  3 //@Component
  4 public class SnowflakeIdWorker {
  5     // 起始的时间戳（自定义，例如系统上线时间）
  6     private final long twepoch = 1732162441000L;
  7 
  8     // 机器id所占的位数
  9     private final long workerIdBits = 5L;
 10 
 11     // 数据标识id所占的位数
 12     private final long datacenterIdBits = 5L;
 13 
 14     // 最大机器ID
 15     private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
 16 
 17     // 最大数据标识ID
 18     private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
 19 
 20     // 序列在id中占的位数
 21     private final long sequenceBits = 12L;
 22 
 23     // 机器ID左移12位
 24     private final long workerIdShift = sequenceBits;
 25 
 26     // 数据标识id左移17位(12+5)
 27     private final long datacenterIdShift = sequenceBits + workerIdBits;
 28 
 29     // 时间截左移22位(5+5+12)
 30     private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
 31 
 32     // 序列的掩码，这里为4095 (0b111111111111=4095)
 33     private final long sequenceMask = -1L ^ (-1L << sequenceBits);
 34 
 35     // 上次生成ID的时间截
 36     private long lastTimestamp = -1L;
 37 
 38     // 序列号
 39     private long sequence = 0L;
 40 
 41     // 工作机器ID
 42     private final long workerId;
 43 
 44     // 数据中心ID
 45     private final long datacenterId;
 46 
 47     public SnowflakeIdWorker(long workerId, long datacenterId) {
 48         if (workerId > maxWorkerId || workerId < 0) {
 49             throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
 50         }
 51         if (datacenterId > maxDatacenterId || datacenterId < 0) {
 52             throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
 53         }
 54         this.workerId = workerId;
 55         this.datacenterId = datacenterId;
 56     }
 57 
 58     // 生成ID
 59     public synchronized long nextId() {
 60         long timestamp = timeGen();
 61 
 62         // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退，抛出异常
 63         if (timestamp < lastTimestamp) {
 64             throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
 65         }
 66 
 67         // 如果时间戳相同，则序列号自增
 68         if (lastTimestamp == timestamp) {
 69             sequence = (sequence + 1) & sequenceMask;
 70             // 序列号溢出，等待下一毫秒
 71             if (sequence == 0) {
 72                 timestamp = tilNextMillis(lastTimestamp);
 73             }
 74         } else {
 75             // 时间戳改变，序列号重置为0
 76             sequence = 0L;
 77         }
 78 
 79         // 更新最后的时间戳
 80         lastTimestamp = timestamp;
 81 
 82         // 移位并通过或运算拼到一起组成64位的ID
 83         return ((timestamp - twepoch) << timestampLeftShift) |
 84                 (datacenterId << datacenterIdShift) |
 85                 (workerId << workerIdShift) |
 86                 sequence;
 87     }
 88 
 89     // 获取当前时间戳
 90     protected long timeGen() {
 91         return System.currentTimeMillis();
 92     }
 93 
 94     // 等待下一个毫秒
 95     protected long tilNextMillis(long lastTimestamp) {
 96         long timestamp = timeGen();
 97         while (timestamp <= lastTimestamp) {
 98             timestamp = timeGen();
 99         }
100         return timestamp;
101     }
102 
103     public static void main(String[] args) {
104         SnowflakeIdWorker idWorker = new SnowflakeIdWorker(1, 1);
105         long start = System.currentTimeMillis();
106         for (int i = 0; i < 100000L; i++) {
107             System.out.println(idWorker.nextId());
108         }
109         System.out.println(System.currentTimeMillis() - start);
110     }
111 }