java中使用雪花算法(Snowflake)为分布式系统生成全局唯一ID代码示例

public class SnowflakeIdWorker {  
    // 起始的时间戳（自定义，例如系统上线时间）  
    private final long twepoch = 1288834974657L;  
  
    // 机器id所占的位数  
    private final long workerIdBits = 5L;  
  
    // 数据标识id所占的位数  
    private final long datacenterIdBits = 5L;  
  
    // 最大机器ID  
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);  
  
    // 最大数据标识ID  
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);  
  
    // 序列在id中占的位数  
    private final long sequenceBits = 12L;  
  
    // 机器ID左移12位  
    private final long workerIdShift = sequenceBits;  
  
    // 数据标识id左移17位(12+5)  
    private final long datacenterIdShift = sequenceBits + workerIdBits;  
  
    // 时间截左移22位(5+5+12)  
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;  
  
    // 序列的掩码，这里为4095 (0b111111111111=4095)  
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);  
  
    // 上次生成ID的时间截  
    private long lastTimestamp = -1L;  
  
    // 序列号  
    private long sequence = 0L;  
  
    // 工作机器ID  
    private final long workerId;  
  
    // 数据中心ID  
    private final long datacenterId;  
  
    public SnowflakeIdWorker(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;  
    }    
  
    // 生成ID  
    public synchronized long nextId() {  
        long timestamp = timeGen();  
  
        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退，抛出异常  
        if (timestamp < lastTimestamp) {  
            throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));  
        }  
  
        // 如果时间戳相同，则序列号自增  
        if (lastTimestamp == timestamp) {  
            sequence = (sequence + 1) & sequenceMask;  
            // 序列号溢出，等待下一毫秒  
            if (sequence == 0) {  
                timestamp = tilNextMillis(lastTimestamp);  
            }  
        } else {  
            // 时间戳改变，序列号重置为0  
            sequence = 0L;  
        }  
  
        // 更新最后的时间戳  
        lastTimestamp = timestamp;  
  
        // 移位并通过或运算拼到一起组成64位的ID  
        return ((timestamp - twepoch) << timestampLeftShift) |  
               (datacenterId << datacenterIdShift) |  
               (workerId << workerIdShift) |  
               sequence;  
    }  
  
    // 获取当前时间戳  
    protected long timeGen() {  
        return System.currentTimeMillis();  
    }  
  
    // 等待下一个毫秒  
    protected long tilNextMillis(long lastTimestamp) {  
        long timestamp = timeGen();  
        while (timestamp <= lastTimestamp) {  
            timestamp = timeGen();  
        }  
        return timestamp;  
    }

    public static void main(String[] args) {  
        SnowflakeIdWorker idWorker = new SnowflakeIdWorker(1, 1);  
        for (int i = 0; i < 5; i++) {  
            long id = idWorker.nextId();  
            System.out.println(Long.toBinaryString(id));  
            System.out.println(id);  
        }  
    }  
}