java方面的雪花算法工具类

以下是一个Java实现的雪花算法工具类，用于生成唯一的ID。

public class SnowflakeIdGenerator {
    
    private static final long START_TIME = 1609459200000L; // 2021-01-01 00:00:00
    private static final long WORKER_ID_BITS = 5L;
    private static final long DATACENTER_ID_BITS = 5L;
    private static final long SEQUENCE_BITS = 12L;
    private static final long MAX_WORKER_ID = -1L ^ (-1L << WORKER_ID_BITS);
    private static final long MAX_DATACENTER_ID = -1L ^ (-1L << DATACENTER_ID_BITS);
    private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;
    private static final long DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTER_ID_BITS;
    private static final long SEQUENCE_MASK = -1L ^ (-1L << SEQUENCE_BITS);
    
    private final long workerId;
    private final long datacenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;
    
    public 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_DATACENTER_ID));
        }
        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) & SEQUENCE_MASK;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        return ((timestamp - START_TIME) << TIMESTAMP_LEFT_SHIFT) |
                (datacenterId << DATACENTER_ID_SHIFT) |
                (workerId << WORKER_ID_SHIFT) |
                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);
long id = idGenerator.nextId();
System.out.println(id);