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package com.mashibing.common.utils;
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import com.mashibing.common.enums.ExceptionEnums;
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import com.mashibing.common.exception.ApiException;
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import org.springframework.beans.factory.annotation.Value;
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import org.springframework.stereotype.Component;
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import javax.annotation.PostConstruct;
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/**
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* @author heqijun
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* @ClassName: SnowFlakeUtil
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* @Description: 雪花算法生成唯一id
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* @date 2025/6/7 16:40
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*/
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@Component
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public class SnowFlakeUtil {
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/**
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* 雪花算法生成全局唯一ID
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* 64个bit为的long类型的值
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* 第一位：占1个bit位，就是0.
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* 第二位：占41个bit位，代表时间戳
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* 第三位：占5个bit位，代表机器id
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* 第四位：占5个bit位，服务id
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* 第五位：占12个bit位，序列，自增的数值
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*/
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/**
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* 41个bit位存储时间戳，从0开始计算，最多可以存储69.7年。
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* 那么如果默认使用，从1970年到现在，最多可以用到2039年左右。
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* 按照从2022-11-11号开始计算，存储41个bit为，这样最多可以使用到2092年不到~~
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*/
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private final long timeStart = 1668096000000L;
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/**
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* 机器id
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*/
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@Value("${snowflake.machineId:0}")
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private long machineId;
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/**
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* 服务id
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*/
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@Value("${snowflake.serviceId:0}")
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private long serviceId;
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/**
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* 序列
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*/
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private long sequence;
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/**
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* 机器id占用的bit位数
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*/
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private final long machineIdBits = 5L;
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/**
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* 服务id占用的bit位数
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*/
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private final long serviceIdBits = 5L;
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/**
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* 序列占用的bit位数
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*/
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private final long sequenceBits = 12L;
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/**
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* 计算出机器id的最大值
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*/
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private long maxMachineId = ~(-1 << machineIdBits);
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/**
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* 计算出服务id的最大值
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*/
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private long maxServiceId = ~(-1 << serviceIdBits);
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@PostConstruct
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public void init() {
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if (machineId > maxMachineId || serviceId > maxServiceId) {
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System.out.println("机器ID或服务ID超过最大范围值！！");
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throw new ApiException(ExceptionEnums.SNOWFLAKE_OUT_OF_RANGE);
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}
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}
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/**
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* 服务id需要位移的位数
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*/
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private long serviceIdShift = sequenceBits;
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/**
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* 机器id需要位移的位数
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*/
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private long machineIdShift = sequenceBits + serviceIdBits;
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/**
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* 时间戳需要位移的位数
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*/
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private long timestampShift = sequenceBits + serviceIdBits + machineIdBits;
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/**
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* 序列的最大值
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*/
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private long maxSequenceId = ~(-1 << sequenceBits);
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/**
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* 记录最近一次获取id的时间
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*/
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private long lastTimestamp = -1;
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/**
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* 获取系统时间毫秒值
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*
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* @return
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*/
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private long timeGen() {
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return System.currentTimeMillis();
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}
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public synchronized long nextId() {
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//1、 拿到当前系统时间的毫秒值
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long timestamp = timeGen();
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// 避免时间回拨造成出现重复的id
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if (timestamp < lastTimestamp) {
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// 说明出现了时间回拨
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System.out.println("当前服务出现时间回拨！！！");
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throw new ApiException(ExceptionEnums.SNOWFLAKE_TIME_BACK);
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}
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//2、 判断当前生成id的时间和上一次生成的时间
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if (timestamp == lastTimestamp) {
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// 同一毫秒值生成id
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sequence = (sequence + 1) & maxSequenceId;
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// 0000 10100000 :sequence
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// 1111 11111111 :maxSequenceId
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if (sequence == 0) {
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// 进到这个if，说明已经超出了sequence序列的最大取值范围
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// 需要等到下一个毫秒再做回来生成具体的值
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timestamp = timeGen();
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while (timestamp <= lastTimestamp) {
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// 时间还没动。
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timestamp = timeGen();
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}
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}
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} else {
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// 另一个时间点生成id
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sequence = 0;
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}
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//3、重新给lastTimestamp复制
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lastTimestamp = timestamp;
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//4、计算id，将几位值拼接起来。 41bit位的时间，5位的机器，5位的服务 ，12位的序列
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return ((timestamp - timeStart) << timestampShift) |
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(machineId << machineIdShift) |
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(serviceId << serviceIdShift) |
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sequence &
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Long.MAX_VALUE;
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}
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}
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heqijun
4 months ago