分布式主键生成方案（雪花算法 java）

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最新推荐文章于 2025-04-07 08:00:00 发布

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分类专栏： java 文章标签： java 分布式主键分布式唯一id

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本文深入解析了SnowFlake算法，一种生成唯一ID的方法，详细介绍了其内部结构，包括时间戳、工作节点ID、数据中心ID及序列号的位分配策略，展示了如何通过这些参数避免ID重复，确保全球范围内ID的唯一性。

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/**
 * @Author: jerry
 * @date: 2019/5/18 22:24
 * @Description：生成唯一ID
 */
public class SnowFlakeIdGenerator {
    // The initial time(2019-01-01)
    private static final long INITIAL_TIME_STAMP = 1546272000000L;

    // Machine ID bits
    private static final long WORK_ID_BITS = 5L;

    // DataCenter ID bits
    private static final long DATACENTER_ID_BITS = 5L;

    // The maximum machine ID supported is 31, which can quickly calculate the maximum decimal number that a few binary numbers can represent.
    private static final long MAX_WORKER_ID = ~(-1L << WORK_ID_BITS);

    // The maximum datacenter ID supported is 31
    private static final long MAX_DATACENTER_ID = ~(-1L << DATACENTER_ID_BITS);

    // Sequence ID bits
    private static final long SEQUENCE_BITS = 12L;

    // The machine ID offset,12
    private static final long WORKERID_OFFSET = SEQUENCE_BITS;

    // The datacent ID offset,12+5
    private static final long DATACENTERID_OFFSET = WORK_ID_BITS + SEQUENCE_BITS;

    // The timestape offset, 5+5+12
    private static final long TIMESTAMP_OFFSET = DATACENTER_ID_BITS + WORK_ID_BITS + SEQUENCE_BITS;

    // Sequence mask,4095
    private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);

    // Worker ID ,0~31
    private long workerId;

    // Datacenter ID,0~31
    private long datacenterId;

    // Sequence,0~4095
    private long sequence = 0L;

    // Last timestamp
    private long lastTimestamp = -1L;

    private static SnowFlakeIdGenerator instance = new SnowFlakeIdGenerator(0, 0);

    public static SnowFlakeIdGenerator getInstance() {
        return instance;
    }


    private SnowFlakeIdGenerator(long workerId, long datacenterId) {
        if (workerId > MAX_WORKER_ID || workerId < 0) {
            throw new IllegalArgumentException(String.format("WorkerID can't be greater than %d or less than 0", MAX_WORKER_ID));
        }
        if (datacenterId > MAX_DATACENTER_ID || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("DataCenterID can't be greater than %d or less than 0", MAX_WORKER_ID));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized long nextId() {
        long timeStamp = System.currentTimeMillis();
        if (timeStamp < lastTimestamp) {
            throw new RuntimeException("The current time less than last time");
        }
        if (timeStamp == lastTimestamp) {
            sequence = (sequence + 1) & SEQUENCE_MASK;
            if (0 == sequence) {
                timeStamp = tillNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timeStamp;

        return (timeStamp - INITIAL_TIME_STAMP) << TIMESTAMP_OFFSET | (datacenterId << DATACENTERID_OFFSET) | (workerId << WORKERID_OFFSET) | sequence;
    }

    private long tillNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <= lastTimestamp) {
            timestamp = System.currentTimeMillis();
        }
        return timestamp;
    }

    public static void main(String[] args) {
        SnowFlakeIdGenerator snowFlake = new SnowFlakeIdGenerator(0, 0);
        // SnowFlake  snowFlake = new SnowFlake(9, 20);
        for (int i = 0; i < (1 << 12); i++) {
            System.out.println(snowFlake.nextId());
        }
    }
}