package com.gkhy.safePlatform.commons.utils.idService; import java.lang.management.ManagementFactory; import java.net.InetAddress; import java.net.NetworkInterface; public class SnowFlake { // 起始的时间戳 private final static long START_STMP = 1577808000000L; //2020-01-01 // 每一部分占用的位数,就三个 private final static long SEQUENCE_BIT = 12; //序列号占用的位数 private final static long MACHINE_BIT = 5; //机器标识占用的位数 private final static long DATACENTER_BIT = 5; //数据中心占用的位数 // 每一部分最大值 private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT); private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT); private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT); // 每一部分向左的位移 private final static long MACHINE_LEFT = SEQUENCE_BIT; private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT; private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT; private long datacenterId; //数据中心 private long machineId; //机器标识 private long sequence = 0L; //序列号 private long lastStmp = -1L; //上一次时间戳 public SnowFlake(long datacenterId, long machineId) { if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) { throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0"); } if (machineId > MAX_MACHINE_NUM || machineId < 0) { throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0"); } this.datacenterId = datacenterId; this.machineId = machineId; } //产生下一个ID public synchronized long nextId() { long currStmp = timeGen(); if (currStmp < lastStmp) { throw new RuntimeException("Clock moved backwards. Refusing to generate id"); } if (currStmp == lastStmp) { //if条件里表示当前调用和上一次调用落在了相同毫秒内,只能通过第三部分,序列号自增来判断为唯一,所以+1. sequence = (sequence + 1) & MAX_SEQUENCE; //同一毫秒的序列数已经达到最大,只能等待下一个毫秒 if (sequence == 0L) { currStmp = getNextMill(); } } else { //不同毫秒内,序列号置为0 //执行到这个分支的前提是currTimestamp > lastTimestamp,说明本次调用跟上次调用对比,已经不再同一个毫秒内了,这个时候序号可以重新回置0了。 sequence = 0L; } lastStmp = currStmp; //就是用相对毫秒数、机器ID和自增序号拼接 return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分 | datacenterId << DATACENTER_LEFT //数据中心部分 | machineId << MACHINE_LEFT //机器标识部分 | sequence; //序列号部分 } private long getNextMill() { long mill = timeGen(); while (mill <= lastStmp) { mill = timeGen(); } return mill; } private long timeGen() { return System.currentTimeMillis(); } /* //测试 public static void main(String[] args) { SnowFlake snowFlow = new SnowFlake(); // for (int i = 0; i < 3; i++) { // System.out.println(snowFlow.nextId()); // } System.out.println(snowFlow.nextId()); }*/ }