id生成器 sonwFlake算法

/*
* Copyright (c) 2014 xiaomaihd and/or its affiliates.All Rights Reserved.
* http://www.xiaomaihd.com
*/

import lombok.extern.slf4j.Slf4j;

/**
* Created by YangFan on 15/4/21 下午6:34.
*

*/
@Slf4j
public class IdWorker {
private final long workerId;
private final static long twepoch = 1361753741828L;
private long sequence = 0L;
//机器标识位数
private final static long workerIdBits = 5L;
//机器ID最大值
public final static long maxWorkerId = -1L ^ -1L << workerIdBits;
//毫秒内自增位
private final static long sequenceBits = 10L;
//机器ID偏左移位
private final static long workerIdShift = sequenceBits;
//时间毫秒左移
private final static long timestampLeftShift = sequenceBits + workerIdBits;
public final static long sequenceMask = -1L ^ -1L << sequenceBits;

private long lastTimestamp = -1L;

public IdWorker(final long workerId) {
super();
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException(String.format(
"worker Id can't be greater than %d or less than 0",
maxWorkerId));
}
this.workerId = workerId;
}

public synchronized long nextId() {
long timestamp = this.timeGen();
if (this.lastTimestamp == timestamp) {
//当前毫秒内，则+1
this.sequence = (this.sequence + 1) & sequenceMask;
if (this.sequence == 0) {
System.out.println("###########" + sequenceMask);
//当前毫秒内计数满了，则等待下一秒
timestamp = this.tilNextMillis(this.lastTimestamp);
}
} else {
this.sequence = 0;
}
//时间错误

if (timestamp < this.lastTimestamp) {
try {
throw new Exception(
String.format(
"Clock moved backwards. Refusing to generate id for %d milliseconds",
this.lastTimestamp - timestamp));
} catch (Exception e) {
log.error(e.getMessage(), e);
}
}

this.lastTimestamp = timestamp;
//ID偏移组合生成最终的ID，并返回ID
long nextId = ((timestamp - twepoch << timestampLeftShift))
| (this.workerId << workerIdShift) | (this.sequence);
// System.out.println("timestamp:" + timestamp + ",timestampLeftShift:"
// + timestampLeftShift + ",nextId:" + nextId + ",workerId:"
// + workerId + ",sequence:" + sequence);
return nextId;
}

//等待下一个毫秒的到来
private long tilNextMillis(final long lastTimestamp) {
long timestamp = this.timeGen();
while (timestamp <= lastTimestamp) {
timestamp = this.timeGen();
}
return timestamp;
}

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

}

拓展了一层
/*
* Copyright (c) 2014 xiaomaihd and/or its affiliates.All Rights Reserved.
* http://www.xiaomaihd.com
*/
package com.longe.nuclear.util.id;

/**
* Created by YangFan on 15/4/24 下午3:12.
*

* ID工具类
*/
public class IdUtil {

private static IdWorker idWorker = new IdWorker(1);

private IdUtil() {
}

public static long generateId() {
return idWorker.nextId();
}

}

调用IdUtil .generateId()就可以处理并发ID生成问题，这个ID生成的是纯数字 底层是2进制的64位长度，UUID是16进制32位。