(1)需要导入的包

主要用在格式化日FastDateFormat.getInstance("yyyyMMddHHmmssSSS");

<dependency>

    <groupId>commons-lang</groupId>

    <artifactId>commons-lang</artifactId>

    <version>2.6</version>

</dependency>

(2)IdGenerator类

import org.apache.commons.lang3.time.FastDateFormat;

import java.net.InetAddress;

import java.net.UnknownHostException;

/**

 * 与snowflake算法区别,返回字符串id,占用更多字节,但直观从id中看出生成时间

 * 改写了生成时间的format方法

 * @Project concurrency

 */

public enum IdGenerator {

    INSTANCE;

    private long workerId;   //用ip地址最后几个字节标示

    private long datacenterId = 0L; //可配置在properties中,启动时加载,此处默认先写成0

    private long sequence = 0L;

    private long workerIdBits = 8L; //节点ID长度

    private long datacenterIdBits = 2L; //数据中心ID长度,可根据时间情况设定位数

    private long sequenceBits = 12L; //序列号12位

    private long workerIdShift = sequenceBits; //机器节点左移12位

    private long datacenterIdShift = sequenceBits + workerIdBits; //数据中心节点左移14位

    private long sequenceMask = -1L ^ (-1L << sequenceBits); //4095

    private long lastTimestamp = -1L;

    private static final FastDateFormat FAST_DATE_FORMAT = FastDateFormat.getInstance("yyyyMMddHHmmssSSS");

    IdGenerator(){

        workerId = 0x000000FF & getLastIP();

    }

    public synchronized String nextId() {

        long timestamp = timeGen(); //获取当前毫秒数

        //如果服务器时间有问题(时钟后退) 报错。

        if (timestamp < lastTimestamp) {

            throw new RuntimeException(String.format(

                    "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));

        }

        //如果上次生成时间和当前时间相同,在同一毫秒内

        if (lastTimestamp == timestamp) {

            //sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位

            sequence = (sequence + 1) & sequenceMask;

            //判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0

            if (sequence == 0) {

                timestamp = tilNextMillis(lastTimestamp); //自旋等待到下一毫秒

            }

        } else {

            sequence = 0L; //如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加

        }

        lastTimestamp = timestamp;

        long suffix = (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;

        //String datePrefix = DateFormatUtils.format(timestamp, "yyyyMMddHHmmssSSS");

        String datePrefix = FAST_DATE_FORMAT.format(timestamp);

        return datePrefix + suffix;

    }

    protected long tilNextMillis(long lastTimestamp) {

        long timestamp = timeGen();

        while (timestamp <= lastTimestamp) {

            timestamp = timeGen();

        }

        return timestamp;

    }

    protected long timeGen() {

        return System.currentTimeMillis();

    }

    private byte getLastIP(){

        byte lastip = 0;

        try{

            InetAddress ip = InetAddress.getLocalHost();

            byte[] ipByte = ip.getAddress();

            lastip = ipByte[ipByte.length - 1];

        } catch (UnknownHostException e) {

            e.printStackTrace();

        }

        return lastip;

    }

}

(3)使用举例

String id = IdGenerator.INSTANCE.nextId()