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    1.         <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
    2.         <dependency>
    3.             <groupId>org.apache.commons</groupId>
    4.             <artifactId>commons-lang3</artifactId>
    5.             <version>3.11</version>
    6.         </dependency>
    1. package com.example.demo.雪花算法;
    3. import lombok.extern.slf4j.Slf4j;
    4. import org.apache.commons.lang3.StringUtils;
    5. import org.springframework.util.Assert;
    7. import java.lang.management.ManagementFactory;
    8. import java.net.InetAddress;
    9. import java.net.NetworkInterface;
    10. import java.util.concurrent.ThreadLocalRandom;
    12. @Slf4j
    13. public class Sequence {
    15.     /**
    16.      * 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
    17.      */
    18.     private final long twepoch = 1288834974657L;
    19.     /**
    20.      * 机器标识位数
    21.      */
    22.     private final long workerIdBits = 5L;
    23.     private final long datacenterIdBits = 5L;
    24.     private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    25.     private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    26.     /**
    27.      * 毫秒内自增位
    28.      */
    29.     private final long sequenceBits = 12L;
    30.     private final long workerIdShift = sequenceBits;
    31.     private final long datacenterIdShift = sequenceBits + workerIdBits;
    32.     /**
    33.      * 时间戳左移动位
    34.      */
    35.     private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    36.     private final long sequenceMask = -1L ^ (-1L << sequenceBits);
    38.     private final long workerId;
    40.     /**
    41.      * 数据标识 ID 部分
    42.      */
    43.     private final long datacenterId;
    44.     /**
    45.      * 并发控制
    46.      */
    47.     private long sequence = 0L;
    48.     /**
    49.      * 上次生产 ID 时间戳
    50.      */
    51.     private long lastTimestamp = -1L;
    53.     public Sequence() {
    54.         this.datacenterId = getDatacenterId(maxDatacenterId);
    55.         this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
    56.     }
    58.     /**
    59.      * 有参构造器
    60.      *
    61.      * @param workerId     工作机器 ID
    62.      * @param datacenterId 序列号
    63.      */
    64.     public Sequence(long workerId, long datacenterId) {
    65.         Assert.isTrue(!(workerId > maxWorkerId || workerId < 0),
    66.                 String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
    67.         Assert.isTrue(!(datacenterId > maxDatacenterId || datacenterId < 0),
    68.                 String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
    69.         this.workerId = workerId;
    70.         this.datacenterId = datacenterId;
    71.     }
    73.     /**
    74.      * 获取 maxWorkerId
    75.      */
    76.     protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
    77.         StringBuilder mpid = new StringBuilder();
    78.         mpid.append(datacenterId);
    79.         String name = ManagementFactory.getRuntimeMXBean().getName();
    80.         if (StringUtils.isNotBlank(name)) {
    81.             /*
    82.              * GET jvmPid
    83.              */
    84.             mpid.append(name.split("@")[0]);
    85.         }
    86.         /*
    87.          * MAC + PID 的 hashcode 获取16个低位
    88.          */
    89.         return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
    90.     }
    92.     /**
    93.      * 数据标识id部分
    94.      */
    95.     protected static long getDatacenterId(long maxDatacenterId) {
    96.         long id = 0L;
    97.         try {
    98.             InetAddress ip = InetAddress.getLocalHost();
    99.             NetworkInterface network = NetworkInterface.getByInetAddress(ip);
    100.             if (network == null) {
    101.                 id = 1L;
    102.             } else {
    103.                 byte[] mac = network.getHardwareAddress();
    104.                 if (null != mac) {
    105.                     id = ((0x000000FF & (long) mac[mac.length - 2]) | (0x0000FF00 & (((long) mac[mac.length - 1]) << 8))) >> 6;
    106.                     id = id % (maxDatacenterId + 1);
    107.                 }
    108.             }
    109.         } catch (Exception e) {
    110.             log.warn(" getDatacenterId: " + e.getMessage());
    111.         }
    112.         return id;
    113.     }
    115.     /**
    116.      * 获取下一个 ID
    117.      *
    118.      * @return 下一个 ID
    119.      */
    120.     public synchronized long nextId() {
    121.         long timestamp = timeGen();
    122.         //闰秒
    123.         if (timestamp < lastTimestamp) {
    124.             long offset = lastTimestamp - timestamp;
    125.             if (offset <= 5) {
    126.                 try {
    127.                     wait(offset << 1);
    128.                     timestamp = timeGen();
    129.                     if (timestamp < lastTimestamp) {
    130.                         throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
    131.                     }
    132.                 } catch (Exception e) {
    133.                     throw new RuntimeException(e);
    134.                 }
    135.             } else {
    136.                 throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
    137.             }
    138.         }
    140.         if (lastTimestamp == timestamp) {
    141.             // 相同毫秒内，序列号自增
    142.             sequence = (sequence + 1) & sequenceMask;
    143.             if (sequence == 0) {
    144.                 // 同一毫秒的序列数已经达到最大
    145.                 timestamp = tilNextMillis(lastTimestamp);
    146.             }
    147.         } else {
    148.             // 不同毫秒内，序列号置为 1 - 3 随机数
    149.             sequence = ThreadLocalRandom.current().nextLong(1, 3);
    150.         }
    152.         lastTimestamp = timestamp;
    154.         // 时间戳部分 | 数据中心部分 | 机器标识部分 | 序列号部分
    155.         return ((timestamp - twepoch) << timestampLeftShift)
    156.                 | (datacenterId << datacenterIdShift)
    157.                 | (workerId << workerIdShift)
    158.                 | sequence;
    159.     }
    161.     protected long tilNextMillis(long lastTimestamp) {
    162.         long timestamp = timeGen();
    163.         while (timestamp <= lastTimestamp) {
    164.             timestamp = timeGen();
    165.         }
    166.         return timestamp;
    167.     }
    169.     protected long timeGen() {
    170.         return SystemClock.now();
    171.     }
    173. }
    1. package com.example.demo.雪花算法;
    3. import java.sql.Timestamp;
    4. import java.util.concurrent.Executors;
    5. import java.util.concurrent.ScheduledExecutorService;
    6. import java.util.concurrent.TimeUnit;
    7. import java.util.concurrent.atomic.AtomicLong;
    9. public class SystemClock {
    10.     private final long period;
    11.     private final AtomicLong now;
    13.     private SystemClock(long period) {
    14.         this.period = period;
    15.         this.now = new AtomicLong(System.currentTimeMillis());
    16.         scheduleClockUpdating();
    17.     }
    19.     private static SystemClock instance() {
    20.         return InstanceHolder.INSTANCE;
    21.     }
    23.     public static long now() {
    24.         return instance().currentTimeMillis();
    25.     }
    27.     public static String nowDate() {
    28.         return new Timestamp(instance().currentTimeMillis()).toString();
    29.     }
    31.     private void scheduleClockUpdating() {
    32.         ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor(runnable -> {
    33.             Thread thread = new Thread(runnable, "System Clock");
    34.             thread.setDaemon(true);
    35.             return thread;
    36.         });
    37.         scheduler.scheduleAtFixedRate(() -> now.set(System.currentTimeMillis()), period, period, TimeUnit.MILLISECONDS);
    38.     }
    40.     private long currentTimeMillis() {
    41.         return now.get();
    42.     }
    44.     private static class InstanceHolder {
    45.         public static final SystemClock INSTANCE = new SystemClock(1);
    46.     }
    47. }