package tech.powerjob.server.core.uid;
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/**
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* Twitter SnowFlake(Scala -> Java)
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*
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* @author tjq
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* @since 2020/4/6
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*/
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public class SnowFlakeIdGenerator {
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/**
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* 起始的时间戳(a special day for me)
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*/
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private final static long START_STAMP = 1555776000000L;
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/**
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* 序列号占用的位数
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*/
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private final static long SEQUENCE_BIT = 6;
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/**
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* 机器标识占用的位数
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*/
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private final static long MACHINE_BIT = 14;
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/**
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* 数据中心占用的位数
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*/
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private final static long DATA_CENTER_BIT = 2;
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/**
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* 每一部分的最大值
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*/
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private final static long MAX_DATA_CENTER_NUM = ~(-1L << DATA_CENTER_BIT);
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private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
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private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
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/**
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* 每一部分向左的位移
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*/
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private final static long MACHINE_LEFT = SEQUENCE_BIT;
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private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
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private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;
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/**
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* 数据中心
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*/
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private final long dataCenterId;
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/**
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* 机器标识
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*/
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private final long machineId;
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/**
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* 序列号
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*/
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private long sequence = 0L;
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/**
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* 上一次时间戳
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*/
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private long lastTimestamp = -1L;
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public SnowFlakeIdGenerator(long dataCenterId, long machineId) {
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if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {
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throw new IllegalArgumentException("dataCenterId can't be greater than MAX_DATA_CENTER_NUM or less than 0");
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}
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if (machineId > MAX_MACHINE_NUM || machineId < 0) {
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throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
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}
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this.dataCenterId = dataCenterId;
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this.machineId = machineId;
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}
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/**
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* 产生下一个ID
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*/
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public synchronized long nextId() {
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long currStamp = getNewStamp();
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if (currStamp < lastTimestamp) {
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return futureId();
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}
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if (currStamp == lastTimestamp) {
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//相同毫秒内,序列号自增
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sequence = (sequence + 1) & MAX_SEQUENCE;
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//同一毫秒的序列数已经达到最大
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if (sequence == 0L) {
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currStamp = getNextMill();
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}
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} else {
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//不同毫秒内,序列号置为0
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sequence = 0L;
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}
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lastTimestamp = currStamp;
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return (currStamp - START_STAMP) << TIMESTAMP_LEFT //时间戳部分
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| dataCenterId << DATA_CENTER_LEFT //数据中心部分
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| machineId << MACHINE_LEFT //机器标识部分
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| sequence; //序列号部分
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}
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/**
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* 发生时钟回拨时借用未来时间生成Id,避免运行过程中任务调度和工作流直接进入不可用状态
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* 注:该方式不可解决原算法中停服状态下时钟回拨导致的重复id问题
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*/
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private long futureId() {
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sequence = (sequence + 1) & MAX_SEQUENCE;
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if (sequence == 0L) {
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lastTimestamp = lastTimestamp + 1;
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}
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return (lastTimestamp - START_STAMP) << TIMESTAMP_LEFT //时间戳部分
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| dataCenterId << DATA_CENTER_LEFT //数据中心部分
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| machineId << MACHINE_LEFT //机器标识部分
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| sequence; //序列号部分
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}
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private long getNextMill() {
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long mill = getNewStamp();
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while (mill <= lastTimestamp) {
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mill = getNewStamp();
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}
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return mill;
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}
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private long getNewStamp() {
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return System.currentTimeMillis();
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}
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}
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