【Spring Boot】自定义雪花算法生成ID

雪花算法（Snowflake）是一种生成唯一ID的分布式算法，由Twitter推出。它能生成不重复的、有时间顺序的全局唯一ID。一个典型的Snowflake ID由64位组成，通常划分如下：

• 1位符号位（始终为0，表示正数）
• 41位时间戳（毫秒级，表示当前时间相对于某个开始时间的偏移）
• 10位机器标识（通常分为数据中心ID和机器ID）
• 12位序列号（表示毫秒内的计数器）

下面是一个自定义的雪花算法来生成唯一的ID。这个实现类似于Twitter的Snowflake算法，并考虑到了线程安全。

public class SnowflakeIDGenerator {

    // 起始时间戳（2020-01-01 00:00:00）
    private final long twepoch = 1577836800000L;

    // 每部分占用的位数
    private final long workerIdBits = 5L;
    private final long datacenterIdBits = 5L;
    private final long sequenceBits = 12L;

    // 最大值
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);

    // 位移
    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    // 掩码
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public SnowflakeIDGenerator(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized long nextId() {
        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift)
                | sequence;
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        SnowflakeIDGenerator generator = new SnowflakeIDGenerator(1, 1);
        for (int i = 0; i < 10; i++) {
            System.out.println(generator.nextId());
        }
    }
}

说明

使用示例

运行上述代码，你会看到生成的唯一ID，它们是按时间顺序递增的，每个ID包含了时间戳、数据中心ID、工作节点ID和序列号的信息。