package com.nanjing.water.common.util;
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public class SnowFlakeUtil {
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/**
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* 起始的时间戳(2020-05-27 00:00:00)
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*/
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private final static long START_STAMP = 1590508800000L;
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/**
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* 每一部分占用的位数
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*/
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//序列号占用的位数
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private final static long SEQUENCE_BIT = 12;
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//机器标识占用的位数
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private final static long MACHINE_BIT = 5;
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//数据中心占用的位数
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private final static long DATA_CENTER_BIT = 5;
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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 ^ (-1L << DATA_CENTER_BIT);
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private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
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private final static long MAX_SEQUENCE = -1L ^ (-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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* 单例模式
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*/
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private static SnowFlakeUtil snowFlake;
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static {
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snowFlake = new SnowFlakeUtil(1L, 2L);
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}
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public static long getId() {
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return snowFlake.nextId();
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}
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public static long getId(long machineId) {
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return SnowFlakeUtil.getId(1L, machineId);
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}
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public static long getId(long dataCenterId, long machineId) {
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return new SnowFlakeUtil(dataCenterId, machineId).nextId();
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}
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//数据中心
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private long dataCenterId;
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//机器标识
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private long machineId;
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//序列号
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private long sequence = 0L;
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//上一次时间戳
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private long lastStamp = -1L;
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private SnowFlakeUtil(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 < lastStamp) {
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throw new RuntimeException("Clock moved backwards. Refusing to generate id");
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}
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if (currStamp == lastStamp) {
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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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lastStamp = 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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private long getNextMill() {
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long mill = getNewStamp();
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while (mill <= lastStamp) {
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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 LocalDateTimeUtil.nowTimeStamp();
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}
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}
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