java雪花算法工具类

以下是一个Java雪花算法工具类的示例：

public class SnowflakeIdGenerator {

    private final long workerId;
    private final long epoch = 1420070400000L; // 2015-01-01 00:00:00 UTC
    private final long workerIdBits = 5L;
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long sequenceBits = 12L;
    private final long workerIdShift = sequenceBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits;
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

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

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

    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 - epoch) << timestampLeftShift) |
                (workerId << workerIdShift) |
                sequence;
    }

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

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

使用它，只需创建一个新的实例并调用`nextId()`方法即可：

SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1);
long id = idGenerator.nextId();