0          41        51          63
┌────────────┬─────────┬───────────┐
│  timestamp │ dataCtr │  worker   │ sequence
│  (41 bits) │ (5 bits)│  (5 bits) │ (12 bits)
└────────────┴─────────┴───────────┘
         ↑
     64-bit signed long (最高位為符號位，始終為 0 → 實際可用 63 位)

import java.util.ArrayList;
import java.util.Date;
import java.util.List;
/**
 * 雪花ID生成器
 *
 */
public class SnowflakeIdGenerator {
    // ==================== 常量定義 ====================
    private static final long EPOCH = 1609459200000L; // 自定義起始時間：2021-01-01 00:00:00 UTC（毫秒）
    private static final int DATA_CENTER_ID_BITS = 5;
    private static final int WORKER_ID_BITS = 5;
    private static final int SEQUENCE_BITS = 12;
    private static final long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS);   // 31
    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);               // 31
    private static final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BITS);                 // 4095
    private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;                        // 12
    private static final long DATA_CENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;  // 17
    private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATA_CENTER_ID_BITS; // 22
    // ==================== 運行時變量 ====================
    private final long dataCenterId;
    private final long workerId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;
    // ==================== 構(gòu)造函數(shù) ====================
    public SnowflakeIdGenerator(long dataCenterId, long workerId) {
        if (dataCenterId < 0 || dataCenterId > MAX_DATA_CENTER_ID) {
            throw new IllegalArgumentException("dataCenterId must be in [0," + MAX_DATA_CENTER_ID + "]");
        }
        if (workerId < 0 || workerId > MAX_WORKER_ID) {
            throw new IllegalArgumentException("workerId must be in [0," + MAX_WORKER_ID + "]");
        }
        this.dataCenterId = dataCenterId;
        this.workerId = workerId;
    }
    // ==================== 核心方法 ====================
    public synchronized long nextId() {
        long timestamp = currentTimeMillis();
        // ?? 時鐘回撥處理：嚴格模式（拋異常） or 容忍模式（等待/告警）
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(
                String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
                    lastTimestamp - timestamp));
        }
        if (lastTimestamp == timestamp) {
            // 同一毫秒內(nèi)，序列號自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0) {
                // 當前毫秒序列已滿，阻塞至下一毫秒
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 新毫秒，序列號重置為 0
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        // 拼接 ID：(timestamp - epoch) << 22 | dataCenterId << 17 | workerId << 12 | sequence
        return ((timestamp - EPOCH) << TIMESTAMP_LEFT_SHIFT)
            | (dataCenterId << DATA_CENTER_ID_SHIFT)
            | (workerId << WORKER_ID_SHIFT)
            | sequence;
    }
    private long tilNextMillis(long lastTimestamp) {
        long timestamp = currentTimeMillis();
        while (timestamp <= lastTimestamp) {
            timestamp = currentTimeMillis();
        }
        return timestamp;
    }
    private long currentTimeMillis() {
        return System.currentTimeMillis();
    }
    // ==================== 輔助方法：解析 ID（可選） ====================
    public static class IdInfo {
        public final long timestamp;      // 時間戳（毫秒）
        public final long dataCenterId;   // 數(shù)據(jù)中心 ID
        public final long workerId;       // 工作節(jié)點 ID
        public final long sequence;       // 序列號
        public IdInfo(long timestamp, long dataCenterId, long workerId, long sequence) {
            this.timestamp = timestamp;
            this.dataCenterId = dataCenterId;
            this.workerId = workerId;
            this.sequence = sequence;
        }
        public IdInfo(long id) {
            this.timestamp = (id >> TIMESTAMP_LEFT_SHIFT) + EPOCH;
            this.dataCenterId = (id >> DATA_CENTER_ID_SHIFT) & MAX_DATA_CENTER_ID;
            this.workerId = (id >> WORKER_ID_SHIFT) & MAX_WORKER_ID;
            this.sequence = id & MAX_SEQUENCE;
        }
    }
    public static void main(String[] args) {
        SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1, 2);
        List<Long> ids = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            long id = idGenerator.nextId();
            ids.add(id);
            System.out.println(id);
        }
        long id = ids.get(8);
        IdInfo info = new IdInfo(id);
        System.out.println(info);
        //SnowflakeIdGenerator.IdInfo info = SnowflakeIdGenerator.parse(id);
        System.out.println("時間戳: " + new Date(info.timestamp));
        System.out.println("數(shù)據(jù)中心 ID: " + info.dataCenterId);
        System.out.println("工作節(jié)點 ID: " + info.workerId);
        System.out.println("序列號: " + info.sequence);
    }
    /**
     * 解析 Snowflake ID
     *
     * @param id Snowflake ID
     * @return 包含時間戳、數(shù)據(jù)中心 ID、工作節(jié)點 ID 和序列號的結(jié)構(gòu)體
     */
    public static IdInfo parse(long id) {
        long timestamp = (id >> TIMESTAMP_LEFT_SHIFT) + EPOCH;
        long dataCenterId = (id >> DATA_CENTER_ID_SHIFT) & MAX_DATA_CENTER_ID;
        long workerId = (id >> WORKER_ID_SHIFT) & MAX_WORKER_ID;
        long sequence = id & MAX_SEQUENCE;
        return new IdInfo(timestamp, dataCenterId, workerId, sequence);
    }
}