ID Generator算法

算法：7位集群+40位时间戳+7位每秒最大生产个数数

适用于集群下唯一id生成：

public class TimeStampIDGenerator{

    /**
     * workerID must be unique for each node in cluster.
     */
    private long workerID;

    private long sequence = 0;
    private long mark = 0;

    private static final int MAXSEQUENCE = 128;
    private static final int MAXWORKERID = 128;

    private long lastTimeGen;

    private final int workerIDBitWidth = 7;
    private final int timeStampBitWidth = 40;
    private final int sequenceBitWidth = 7;

    private long sequenceLeftShift = 0;
    private long timeStampLeftShift = sequenceBitWidth;
    private long workerIDLeftShift = sequenceBitWidth + timeStampBitWidth;

    /**
     * MillSeconds from January 1, 1970 to November 3rd 2010
     */
    private final long TIMEBASELINE = 1288834974657L;

    public long nextId() {
        synchronized (this) {
            long timeGen = timeGen();
            mark++;
            sequence = (++sequence) % MAXSEQUENCE;
            if (timeGen == lastTimeGen) {
                if (mark >= MAXSEQUENCE) {
                    timeGen = tillNextMill();
                    mark = 0;
                }
            } else {
                mark = 0;
            }
            lastTimeGen = timeGen;

            return sequence << sequenceLeftShift | (timeGen - TIMEBASELINE) << timeStampLeftShift
                    | workerID << workerIDLeftShift;
        }

    }

    public void setWorkerID(long id) {
        if (validateWorkerID(id)) {
            workerID = id;
        } else {
            throw new IllegalStateException("invalid id:" + id);
        }
    }

    private boolean validateWorkerID(long id) {
        if (id > MAXWORKERID || id < 0) {
            return false;
        } else {
            return true;
        }
    }

    private long tillNextMill() {
        long timeGen = timeGen();
        while (timeGen <= lastTimeGen) {
            timeGen = timeGen();
        }
        // System.out.println("i'm in tillNextMill");
        return timeGen;
    }

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

    @Override
    public long generateId() {
        return this.nextId();
    }
}