永不重复的id生成器

目录

• (1)需要导入的包
• (2)IdGenerator类
• (3)使用举例

(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()