Java 雪花算法 workerid生成算法

Java 雪花算法（Snowflake）是一种分布式全局唯一 ID 生成算法，由 Twitter 公司提出。该算法可以在分布式系统中生成唯一 ID，同时也保证了 ID 的有序性和时间戳的精度。其中 workerid 是生成算法中的一个关键因素，下面是一种 Java 实现的 workerid 生成算法：

public class SnowflakeIdGenerator {
    private static final long twepoch = 1288834974657L;
    private static final long workerIdBits = 5L;
    private static final long datacenterIdBits = 5L;
    private static final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private static final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private static final long sequenceBits = 12L;
    private static final long workerIdShift = sequenceBits;
    private static final long datacenterIdShift = sequenceBits + workerIdBits;
    private static final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private static 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();
    }
}

该代码中的 workerid 生成算法使用了位运算和时间戳的方式，通过将 workerid、datacenterid、时间戳和序列号进行位移和或运算，生成一个 64 位的唯一 ID。其中 workerid 和 datacenterid 需要在初始化时传入，可以通过配置文件等方式实现。