Java版雪花算法生成ID实用工具类完整实例

 0          41        51          63
┌────────────┬─────────┬───────────┐
│  timestamp │ datactr │  worker   │ sequence
│  (41 bits) │ (5 bits)│  (5 bits) │ (12 bits)
└────────────┴─────────┴───────────┘
         ↑
     64-bit signed long (最高位为符号位，始终为 0 → 实际可用 63 位)

import java.util.arraylist;
import java.util.date;
import java.util.list;
/**
 * 雪花id生成器
 *
 */
public class snowflakeidgenerator {
    // ==================== 常量定义 ====================
    private static final long epoch = 1609459200000l; // 自定义起始时间：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
    // ==================== 运行时变量 ====================
    private final long datacenterid;
    private final long workerid;
    private long sequence = 0l;
    private long lasttimestamp = -1l;
    // ==================== 构造函数 ====================
    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();
        // ⚠️ 时钟回拨处理：严格模式（抛异常） 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) {
            // 同一毫秒内，序列号自增
            sequence = (sequence + 1) & max_sequence;
            if (sequence == 0) {
                // 当前毫秒序列已满，阻塞至下一毫秒
                timestamp = tilnextmillis(lasttimestamp);
            }
        } else {
            // 新毫秒，序列号重置为 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();
    }
    // ==================== 辅助方法：解析 id（可选） ====================
    public static class idinfo {
        public final long timestamp;      // 时间戳（毫秒）
        public final long datacenterid;   // 数据中心 id
        public final long workerid;       // 工作节点 id
        public final long sequence;       // 序列号
        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("时间戳: " + new date(info.timestamp));
        system.out.println("数据中心 id: " + info.datacenterid);
        system.out.println("工作节点 id: " + info.workerid);
        system.out.println("序列号: " + info.sequence);
    }
    /**
     * 解析 snowflake id
     *
     * @param id snowflake id
     * @return 包含时间戳、数据中心 id、工作节点 id 和序列号的结构体
     */
    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);
    }
}