雪花算法工具类 java

以下是一个简单的雪花算法工具类的 Java 实现：

public class SnowflakeIdGenerator {

    private final long epoch = 1420041600000L; // 起始时间戳，用于缩小时间戳范围，可根据实际情况调整
    private final long workerIdBits = 5L; // 机器 ID 所占位数
    private final long dataCenterIdBits = 5L; // 数据中心 ID 所占位数
    private final long sequenceBits = 12L; // 序列号所占位数

    private final long maxWorkerId = -1L ^ (-1L << workerIdBits); // 机器 ID 最大值
    private final long maxDataCenterId = -1L ^ (-1L << dataCenterIdBits); // 数据中心 ID 最大值
    private final long maxSequence = -1L ^ (-1L << sequenceBits); // 序列号最大值

    private final long workerIdShift = sequenceBits; // 机器 ID 向左移动位数
    private final long dataCenterIdShift = sequenceBits + workerIdBits; // 数据中心 ID 向左移动位数
    private final long timestampShift = sequenceBits + workerIdBits + dataCenterIdBits; // 时间戳向左移动位数

    private long workerId; // 机器 ID
    private long dataCenterId; // 数据中心 ID
    private long sequence = 0L; // 序列号
    private long lastTimestamp = -1L; // 上次生成的时间戳

    public SnowflakeIdGenerator(long workerId, long dataCenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException("Worker ID can't be greater than " + maxWorkerId + " or less than 0");
        }
        if (dataCenterId > maxDataCenterId || dataCenterId < 0) {
            throw new IllegalArgumentException("Data center ID can't be greater than " + maxDataCenterId + " or less than 0");
        }
        this.workerId = workerId;
        this.dataCenterId = dataCenterId;
    }

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

        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards, refusing to generate ID");
        }

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

        lastTimestamp = timestamp;

        return ((timestamp - epoch) << timestampShift) |
                (dataCenterId << dataCenterIdShift) |
                (workerId << workerIdShift) |
                sequence;
    }

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

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

使用方法：

SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1, 1); // 创建一个 ID 生成器，传入机器 ID 和数据中心 ID
long id = idGenerator.nextId(); // 生成 ID

注意事项：

- 如果在同一毫秒内生成的 ID 数量超过了序列号所占的位数，将会进入下一毫秒生成 ID。
- 如果系统时间被回拨，将会抛出异常，应该记录异常并等待时间同步后再生成 ID。