不重複id程式碼生成類

package com.hp.snowflake;
/**
 * An object that generates IDs.
 * This is broken into a separate class in case
 * we ever want to support multiple worker threads
 * per process
 */
public class IdWorker {

    private long workerId;
    private long datacenterId;
    private long sequence = 0
 
L;

    private long twepoch = 1288834974657L;

    private long workerIdBits = 5L;
    private long datacenterIdBits = 5L;
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private long sequenceBits = 12L;

    private
 
 long workerIdShift = sequenceBits;
    private long datacenterIdShift = sequenceBits + workerIdBits;
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long lastTimestamp = -1L;

    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;
    }

    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) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

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

多執行緒測試，生成是否有重複id

package com.hp.snowflake;

import java.util.HashSet;
import java.util.Set;

public class IdWorkerTest {

    static class IdWorkThread implements Runnable {
        private Set<Long> set;
        private IdWorker idWorker;

        public IdWorkThread(Set<Long> set, IdWorker idWorker) {
            this.set = set;
            this.idWorker = idWorker;
        }

        @Override
        public void run() {
            while (true) {
                for(int x=0;x<10000;x++){
                    long id = idWorker.nextId();
                    if (!set.add(id)) {
                        System.out.println("duplicate:" + id);
                    }
                }
            }
        }
    }

    public static void main(String[] args) {
        Set<Long> set = new HashSet<Long>();
         //要單例
        final IdWorker idWorker1 = new IdWorker(1, 1);
        for(int x=0;x<31;x++){
            Thread t1 = new Thread( idWorker1 );
            t1.setDaemon(true);
            t1.start();
        }
    }
}