import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

//雪花算法代码实现
public class IdWorker {
// 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
private final static long twepoch = 1288834974657L;
// 机器标识位数
private final static long workerIdBits = 5L;
// 数据中心标识位数
private final static long datacenterIdBits = 5L;
// 机器ID最大值
private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
// 数据中心ID最大值
private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
// 毫秒内自增位
private final static long sequenceBits = 12L;
// 机器ID偏左移12位
private final static long workerIdShift = sequenceBits;
// 数据中心ID左移17位
private final static long datacenterIdShift = sequenceBits + workerIdBits;
// 时间毫秒左移22位
private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

private final static long sequenceMask = -1L ^ (-1L << sequenceBits);  
/\* 上次生产id时间戳 \*/  
private static long lastTimestamp = -1L;  
// 0，并发控制  
private long sequence = 0L;

private final long workerId;  
// 数据标识id部分  
private final long datacenterId;

public IdWorker(){  
    this.datacenterId = getDatacenterId(maxDatacenterId);  
    this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);  
}  
/\*\*  
 \* @param workerId  
 \*            工作机器ID  
 \* @param datacenterId  
 \*            序列号  
 \*/  
public IdWorker(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;  
}  
/\*\*  
 \* 获取下一个ID  
 \*  
 \* @return  
 \*/  
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) {  
        // 当前毫秒内，则+1  
        sequence = (sequence + 1) & sequenceMask;  
        if (sequence == 0) {  
            // 当前毫秒内计数满了，则等待下一秒  
            timestamp = tilNextMillis(lastTimestamp);  
        }  
    } else {  
        sequence = 0L;  
    }  
    lastTimestamp = timestamp;  
    // ID偏移组合生成最终的ID，并返回ID  
    long nextId = ((timestamp - twepoch) << timestampLeftShift)  
            | (datacenterId << datacenterIdShift)  
            | (workerId << workerIdShift) | sequence;

    return nextId;  
}

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

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

/\*\*  
 \* <p>  
 \* 获取 maxWorkerId  
 \* </p>  
 \*/  
protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {  
    StringBuffer mpid = new StringBuffer();  
    mpid.append(datacenterId);  
    String name = ManagementFactory.getRuntimeMXBean().getName();  
    if (!name.isEmpty()) {  
        /\*  
         \* GET jvmPid  
         \*/  
        mpid.append(name.split("@")\[0\]);  
    }  
    /\*  
     \* MAC + PID 的 hashcode 获取16个低位  
     \*/  
    return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);  
}

/\*\*  
 \* <p>  
 \* 数据标识id部分  
 \* </p>  
 \*/  
protected static long getDatacenterId(long maxDatacenterId) {  
    long id = 0L;  
    try {  
        InetAddress ip = InetAddress.getLocalHost();  
        NetworkInterface network = NetworkInterface.getByInetAddress(ip);  
        if (network == null) {  
            id = 1L;  
        } else {  
            byte\[\] mac = network.getHardwareAddress();  
            id = ((0x000000FF & (long) mac\[mac.length - 1\])  
                    | (0x0000FF00 & (((long) mac\[mac.length - 2\]) << 8))) >> 6;  
            id = id % (maxDatacenterId + 1);  
        }  
    } catch (Exception e) {  
        System.out.println(" getDatacenterId: " + e.getMessage());  
    }  
    return id;  
}  

}