唯一ID生成器–雪花算法

在微服务架构，分布式系统中的操作会有一些全局性ID的需求，所以我们不能用数据库本身的自增功能来产生主键值，只能由程序来生成唯一的主键值。我们采用的是twitter的snokeflake雪花)算法。

说明

程序snokeflake会生成一个64bit的数据，结构如下

最后12位的序列号容纳的大小为4096，同一毫秒，同个机器产生超过这个数的ID，就会自动等待一毫秒，进入下一个时间戳继续计数。

代码

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

/**
 * 雪花算法代码实现
 */
public class IdWorker {
    /**
     *   twepoch:  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 = getDatacenterIdmaxDatacenterId);
        this.workerId = getMaxWorkerIddatacenterId, maxWorkerId);
    }
    /**
     * @param workerId
     *            工作机器ID
     * @param datacenterId
     *            序列号
     */
    public IdWorkerlong workerId, long datacenterId) {
        if workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentExceptionString.format"worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentExceptionString.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 RuntimeExceptionString.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 = tilNextMillislastTimestamp);
            }
        } 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 tilNextMillisfinal 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 getMaxWorkerIdlong datacenterId, long maxWorkerId) {
        StringBuffer mpid = new StringBuffer);
        mpid.appenddatacenterId);
        String name = ManagementFactory.getRuntimeMXBean).getName);
        if !name.isEmpty)) {
            /*
             * GET jvmPid
             */
            mpid.appendname.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 getDatacenterIdlong maxDatacenterId) {
        long id = 0L;
        try {
            InetAddress ip = InetAddress.getLocalHost);
            NetworkInterface network = NetworkInterface.getByInetAddressip);
            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;
    }
}

欢迎批评指正！