package com.fastbee.iot.util;
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public class SnowflakeIdWorker {
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/**
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* 开始时间：2020-01-01 00:00:00
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*/
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private final long beginTs = 1577808000000L;
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private final long workerIdBits = 10;
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/**
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* 2^10 - 1 = 1023
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*/
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private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
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private final long sequenceBits = 12;
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/**
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* 2^12 - 1 = 4095
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*/
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private final long maxSequence = -1L ^ (-1L << sequenceBits);
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/**
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* 时间戳左移22位
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*/
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private final long timestampLeftOffset = workerIdBits + sequenceBits;
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/**
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* 业务ID左移12位
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*/
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private final long workerIdLeftOffset = sequenceBits;
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/**
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* 合并了机器ID和数据标示ID，统称业务ID，10位
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*/
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private long workerId;
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/**
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* 毫秒内序列，12位，2^12 = 4096个数字
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*/
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private long sequence = 0L;
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/**
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* 上一次生成的ID的时间戳，同一个worker中
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*/
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private long lastTimestamp = -1L;
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public SnowflakeIdWorker(long workerId) {
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if (workerId > maxWorkerId || workerId < 0) {
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throw new IllegalArgumentException(String.format("WorkerId必须大于或等于0且小于或等于%d", maxWorkerId));
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}
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this.workerId = workerId;
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}
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public synchronized long nextId() {
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long ts = System.currentTimeMillis();
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if (ts < lastTimestamp) {
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throw new RuntimeException(String.format("系统时钟回退了%d毫秒", (lastTimestamp - ts)));
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}
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// 同一时间内，则计算序列号
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if (ts == lastTimestamp) {
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// 序列号溢出
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if (++sequence > maxSequence) {
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ts = tilNextMillis(lastTimestamp);
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sequence = 0L;
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}
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} else {
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// 时间戳改变，重置序列号
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sequence = 0L;
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}
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lastTimestamp = ts;
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// 0 - 00000000 00000000 00000000 00000000 00000000 0 - 00000000 00 - 00000000 0000
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// 左移后，低位补0，进行按位或运算相当于二进制拼接
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// 本来高位还有个0<<63，0与任何数字按位或都是本身，所以写不写效果一样
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return (ts - beginTs) << timestampLeftOffset | workerId << workerIdLeftOffset | sequence;
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}
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/**
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* 阻塞到下一个毫秒
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*
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* @param lastTimestamp
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* @return
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*/
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private long tilNextMillis(long lastTimestamp) {
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long ts = System.currentTimeMillis();
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while (ts <= lastTimestamp) {
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ts = System.currentTimeMillis();
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}
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return ts;
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}
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public static void main(String[] args) {
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SnowflakeIdWorker snowflakeIdWorker = new SnowflakeIdWorker(1);
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for (int i = 0; i < 10; i++) {
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long id = snowflakeIdWorker.nextId();
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System.out.println(id);
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}
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}
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}
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