package com.fzzy.api.utils;
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public class SnowflakeIdWorker {
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//下面两个每个5位，加起来就是10位的工作机器id
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private static long workerId = 2; //工作id
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private static long datacenterId =2; //数据id
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//12位的序列号
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private static long sequence = 2;
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public SnowflakeIdWorker(long workerId, long datacenterId, long sequence){
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// sanity check for workerId
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if (workerId > maxWorkerId || workerId < 0) {
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throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0",maxWorkerId));
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}
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if (datacenterId > maxDatacenterId || datacenterId < 0) {
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throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0",maxDatacenterId));
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}
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System.out.printf("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d",
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timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId);
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SnowflakeIdWorker.workerId = workerId;
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SnowflakeIdWorker.datacenterId = datacenterId;
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SnowflakeIdWorker.sequence = sequence;
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}
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//初始时间戳
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private static long twepoch = 1645587680;
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//长度为5位
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private static long workerIdBits = 5L;
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private static long datacenterIdBits = 5L;
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//最大值
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private static long maxWorkerId = -1L ^ (-1L << workerIdBits);
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private static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
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//序列号id长度
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private static long sequenceBits = 12L;
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//序列号最大值
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private static long sequenceMask = -1L ^ (-1L << sequenceBits);
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//工作id需要左移的位数，12位
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private static long workerIdShift = sequenceBits;
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//数据id需要左移位数 12+5=17位
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private static long datacenterIdShift = sequenceBits + workerIdBits;
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//时间戳需要左移位数 12+5+5=22位
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private static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
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//上次时间戳，初始值为负数
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private static long lastTimestamp = -1L;
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public static long getWorkerId(){
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return workerId;
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}
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public static long getDatacenterId(){
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return datacenterId;
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}
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public static long getTimestamp(){
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return System.currentTimeMillis();
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}
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//下一个ID生成算法
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public synchronized static long nextId() {
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long timestamp = SnowflakeIdWorker.timeGen();
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//获取当前时间戳如果小于上次时间戳，则表示时间戳获取出现异常
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if (timestamp < lastTimestamp) {
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System.err.printf("clock is moving backwards. Rejecting requests until %d.", lastTimestamp);
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throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
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lastTimestamp - timestamp));
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}
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//获取当前时间戳如果等于上次时间戳（同一毫秒内），则在序列号加一；否则序列号赋值为0，从0开始。
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if (lastTimestamp == timestamp) {
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sequence = (sequence + 1) & sequenceMask;
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if (sequence == 0) {
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timestamp = tilNextMillis(lastTimestamp);
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}
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} else {
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sequence = 0;
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}
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//将上次时间戳值刷新
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lastTimestamp = timestamp;
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/**
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* 返回结果：
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* (timestamp - twepoch) << timestampLeftShift) 表示将时间戳减去初始时间戳，再左移相应位数
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* (datacenterId << datacenterIdShift) 表示将数据id左移相应位数
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* (workerId << workerIdShift) 表示将工作id左移相应位数
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* | 是按位或运算符，例如：x | y，只有当x，y都为0的时候结果才为0，其它情况结果都为1。
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* 因为个部分只有相应位上的值有意义，其它位上都是0，所以将各部分的值进行 | 运算就能得到最终拼接好的id
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*/
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return ((timestamp - twepoch) << timestampLeftShift) |
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(datacenterId << datacenterIdShift) |
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(workerId << workerIdShift) |
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sequence;
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}
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//获取时间戳，并与上次时间戳比较
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private static long tilNextMillis(long lastTimestamp) {
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long timestamp = timeGen();
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while (timestamp <= lastTimestamp) {
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timestamp = timeGen();
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}
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return timestamp;
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}
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//获取系统时间戳
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private static long timeGen(){
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return System.currentTimeMillis();
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}
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//---------------测试---------------
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public static void main(String[] args) {
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// SnowflakeIdWorker snowflakeIdWorker= new SnowflakeIdWorker(2,2,2);
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for (int i = 0; i < 100; i++) {
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System.out.println(SnowflakeIdWorker.nextId());
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}
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}
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}
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