分布式ID生成器

1、新建WorkId类，用于生成工作ID，主要利用ip地址进行转换获得。也可以通过配置文件进行配置获取

package com.hua.common.id;

import org.apache.commons.lang3.RandomUtils;
import org.apache.commons.lang3.StringUtils;

import java.net.Inet4Address;
import java.net.UnknownHostException;

/**
 * @Deacription TODO
 * @Author huazi
 * @Date 2020/4/5 14:29
 **/
public final class WorkId {

    public final static Long generate() {
        try {
            //获取本地ip地址
            String hostAddress = Inet4Address.getLocalHost().getHostAddress();
            int[] ints = StringUtils.toCodePoints(hostAddress);
            int sums = 0;
            for (int b : ints) {
                sums += b;
            }
            return (long) (sums % 32);
        } catch (UnknownHostException e) {
            // 如果获取失败，则使用随机数备用
            return RandomUtils.nextLong(0, 31);
        }
    }
}

2、新建DataCenterId ，用于获取数据中心ID，主要根据其主机名称来获取数据中心ID。数据中心ID也可以从配置文件中设置

package com.hua.common.id;

import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.SystemUtils;

/**
 * @Deacription TODO
 * @Author huazi
 * @Date 2020/4/5 14:31
 **/
public final class DataCenterId {

    public final static Long generate() {
 
        int[] ints = StringUtils.toCodePoints(SystemUtils.getHostName());
        int sums = 0;
        for (int i : ints) {
            sums += i;
        }
        return (long) (sums % 32);
    }

}

3、新建Snowflake，雪花算法核心类

package com.hua.common.id;

/**
 * @Deacription TODO
 * @Author huazi
 * @Date 2020/4/5 14:24
 **/
public class Snowflake {

    /**
     * 开始时间截
     */
    private final long twepoch = 1420041600000L;

    /**
     * 机器id所占的位数
     */
    private final long workerIdBits = 5L;

    /**
     * 数据标识id所占的位数
     */
    private final long datacenterIdBits = 5L;

    /**
     *  支持的最大机器id，结果是31 (这个移位算法可以很快的计算出几位二进制数所能表示的最大十进制数)
     */
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);

    /**
     *  支持的最大数据标识id，结果是31 
     */
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);

    /**
     * 序列在id中占的位数
     */
    private final long sequenceBits = 12L;

    /**
     * 机器ID向左移12位
     */
    private final long workerIdShift = sequenceBits;

    /**
     *  数据标识id向左移17位(12+5)
     */
    private final long datacenterIdShift = sequenceBits + workerIdBits;

    /**
     * 时间截向左移22位(5+5+12)
     */
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    /**
     * 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095)
     */
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    /**
     * 工作机器ID(0~31)
     */
    private long workerId;

    /**
     * 数据中心ID(0~31)
     */
    private long datacenterId;

    /**
     * 毫秒内序列(0~4095)
     */
    private long sequence = 0L;

    /**
     * 上次生成ID的时间截
     */
    private long lastTimestamp = -1L;


    /**
     * 构造函数
     *
     * @param workerId     工作ID (0~31)
     * @param datacenterId 数据中心ID (0~31)
     */
    public Snowflake(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;
    }


    /**
     * 获得下一个ID (该方法是线程安全的)
     *
     * @return SnowflakeId
     */
    public synchronized long nextId() {
        long timestamp = currTimeMill();

        //如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(
                    String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        //如果是同一时间生成的，则进行毫秒内序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            //毫秒内序列溢出
            if (sequence == 0) {
                //阻塞到下一个毫秒,获得新的时间戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        }
        //时间戳改变，毫秒内序列重置
        else {
            sequence = 0L;
        }

        //上次生成ID的时间截
        lastTimestamp = timestamp;

        //移位并通过或运算拼到一起组成64位的ID
        return ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift)
                | sequence;
    }

    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     *
     * @param lastTimestamp 上次生成ID的时间截
     * @return 当前时间戳
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = currTimeMill();
        while (timestamp <= lastTimestamp) {
            timestamp = currTimeMill();
        }
        return timestamp;
    }

   /**
    * 获取当前时间毫秒值
    **/
    protected long currTimeMill() {
        return System.currentTimeMillis();
    }
}

4、新建SequenceId，用于获取ID（使用锁以便其多线程下能够保证其线程安全）

package com.hua.common.id;

/**
 * @Deacription SequenceId 生成器
 * @Author huazi
 * @Date 2020/4/5 14:28
 **/
public final class SequenceId {

    private static Snowflake SNOW_FLAKE = null;

    
    static {
        Long workId = WorkId.generate();
        Long dataCenterId = DataCenterId.generate();
        SNOW_FLAKE = new Snowflake(workId, dataCenterId);
    }
    /**
    * 加锁使其多线程下能够保证其线程安全
    **/
    public synchronized static Long generate() {
        Long id = SNOW_FLAKE.nextId();
        return id;
    }
}