import java.util.UUID;

public class Main {
    public static void main(String[] args) {
        UUID uuid = UUID.randomUUID();
        System.out.println(uuid.toString());
    }
}

import cn.hutool.core.net.NetUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.util.Random;

/**
 * Twitter_Snowflake<br>
 * SnowFlake的結(jié)構(gòu)如下(每部分用-分開(kāi)):<br>
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 -
 * 000000000000 <br>
 * 1位標(biāo)識(shí)，由于long基本類型在Java中是帶符號(hào)的，最高位是符號(hào)位，正數(shù)是0，負(fù)數(shù)是1，所以id一般是正數(shù)，最高位是0<br>
 * 41位時(shí)間截(毫秒級(jí))，注意，41位時(shí)間截不是存儲(chǔ)當(dāng)前時(shí)間的時(shí)間截，而是存儲(chǔ)時(shí)間截的差值（當(dāng)前時(shí)間截 - 開(kāi)始時(shí)間截)
 * 得到的值），這里的的開(kāi)始時(shí)間截，一般是我們的id生成器開(kāi)始使用的時(shí)間，由我們程序來(lái)指定的（如下下面程序IdWorker類的startTime屬性）。41位的時(shí)間截，可以使用69年，年T
 * = (1L << 41) / (1000L * 60 * 60 * 24 * 365) = 69<br>
 * 10位的數(shù)據(jù)機(jī)器位，可以部署在1024個(gè)節(jié)點(diǎn)，包括5位datacenterId和5位workerId<br>
 * 12位序列，毫秒內(nèi)的計(jì)數(shù)，12位的計(jì)數(shù)順序號(hào)支持每個(gè)節(jié)點(diǎn)每毫秒(同一機(jī)器，同一時(shí)間截)產(chǎn)生4096個(gè)ID序號(hào)<br>
 * 加起來(lái)剛好64位，為一個(gè)Long型。<br>
 * SnowFlake的優(yōu)點(diǎn)是，整體上按照時(shí)間自增排序，并且整個(gè)分布式系統(tǒng)內(nèi)不會(huì)產(chǎn)生ID碰撞(由數(shù)據(jù)中心ID和機(jī)器ID作區(qū)分)，并且效率較高，經(jīng)測(cè)試，SnowFlake每秒能夠產(chǎn)生26萬(wàn)ID左右。
 */
@Component
public class SnowflakeIdWorker {
    /**
     * 開(kāi)始時(shí)間截 (2019-06-21)
     */
    private final long twepoch = 1561104939733L;

    /**
     * 機(jī)器id所占的位數(shù)
     */
    private final long workerIdBits = 5L;

    /**
     * 數(shù)據(jù)標(biāo)識(shí)id所占的位數(shù)
     */
    private final long datacenterIdBits = 5L;

    /**
     * 支持的最大機(jī)器id，結(jié)果是31 (這個(gè)移位算法可以很快的計(jì)算出幾位二進(jìn)制數(shù)所能表示的最大十進(jìn)制數(shù))
     */
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);

    /**
     * 支持的最大數(shù)據(jù)標(biāo)識(shí)id，結(jié)果是31
     */
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);

    /**
     * 序列在id中占的位數(shù)
     */
    private final long sequenceBits = 12L;

    /**
     * 機(jī)器ID向左移12位
     */
    private final long workerIdShift = sequenceBits;

    /**
     * 數(shù)據(jù)標(biāo)識(shí)id向左移17位(12+5)
     */
    private final long datacenterIdShift = sequenceBits + workerIdBits;

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

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

    /**
     * 工作機(jī)器ID(0~31)
     */
    private long workerId = getWorkId();

    /**
     * 數(shù)據(jù)中心ID(0~31)
     */
    private long datacenterId = getDataId();

    /**
     * 毫秒內(nèi)序列(0~4095)
     */
    private long sequence = 0L;

    /**
     * 上次生成ID的時(shí)間截
     */
    private long lastTimestamp = -1L;

    /**
     * 機(jī)器隨機(jī)獲取數(shù)據(jù)中中心id的參數(shù) 32
     */
    private final long DATA_RANDOM = maxDatacenterId + 1;

    /**
     * 隨機(jī)獲取的機(jī)器id的參數(shù)
     */
    private final long WORK_RANDOM = maxWorkerId + 1;

    private static final Logger logger = LoggerFactory.getLogger(SnowflakeIdWorker.class);

    @PostConstruct
    public void init() {
        logger.debug("snowflake-work-id：{}", getWorkId());
        logger.debug("snowflake-data-id：{}", getDataId());
    }

    public SnowflakeIdWorker() {
        //  this(0, 0);
    }

    /**
     * 構(gòu)造函數(shù)
     *
     * @param workerId     工作ID (0~31)
     * @param datacenterId 數(shù)據(jù)中心ID (0~31)
     */
    public SnowflakeIdWorker(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;
    }


    /**
     * 獲得下一個(gè)ID (該方法是線程安全的)
     *
     * @return SnowflakeId
     */
    public synchronized long nextId() {
        long timestamp = timeGen();

        // 如果當(dāng)前時(shí)間小于上一次ID生成的時(shí)間戳，說(shuō)明系統(tǒng)時(shí)鐘回退過(guò)這個(gè)時(shí)候應(yīng)當(dāng)拋出異常
        if (timestamp < lastTimestamp) {
            if (lastTimestamp - timestamp < 2000) {
                // 容忍2秒內(nèi)的回?fù)埽苊釴TP校時(shí)造成的異常
                timestamp = lastTimestamp;
            } else {
                // 如果服務(wù)器時(shí)間有問(wèn)題(時(shí)鐘后退) 報(bào)錯(cuò)。
                throw new RuntimeException(String.format(
                        "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
            }
        }

        // 如果是同一時(shí)間生成的，則進(jìn)行毫秒內(nèi)序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            // 毫秒內(nèi)序列溢出
            if (sequence == 0) {
                // 阻塞到下一個(gè)毫秒,獲得新的時(shí)間戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        }
        // 時(shí)間戳改變，毫秒內(nèi)序列重置
        else {
            sequence = 0L;
        }

        // 上次生成ID的時(shí)間截
        lastTimestamp = timestamp;

        // 移位并通過(guò)或運(yùn)算拼到一起組成64位的ID
        return ((timestamp - twepoch) << timestampLeftShift) //
                | (datacenterId << datacenterIdShift) //
                | (workerId << workerIdShift) //
                | sequence;
    }

    /**
     * 阻塞到下一個(gè)毫秒，直到獲得新的時(shí)間戳
     *
     * @param lastTimestamp 上次生成ID的時(shí)間截
     * @return 當(dāng)前時(shí)間戳
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    /**
     * 返回以毫秒為單位的當(dāng)前時(shí)間
     *
     * @return 當(dāng)前時(shí)間(毫秒)
     */
    protected long timeGen() {
        return System.currentTimeMillis();
    }


    /**
     * 根據(jù)host name 取余，發(fā)生異常就獲取0到31之間的隨機(jī)數(shù)
     *
     * @return
     */
    public long getWorkId() {
        try {
            String ip = NetUtil.getLocalhost().getHostAddress();
            logger.info("服務(wù)器IP：{}", ip);
            return getHostId(ip, maxWorkerId);
        } catch (Exception e) {
            return new Random().nextInt((int) WORK_RANDOM);
        }

    }

    /**
     * 根據(jù)host name 取余，發(fā)生異常就獲取0到31之間的隨機(jī)數(shù)
     *
     * @return
     */
    public long getDataId() {

        try {
            String ip = NetUtil.getLocalhost().getHostAddress();
            logger.info("服務(wù)器IP：{}", ip);
            return getHostId(ip, maxDatacenterId);
        } catch (Exception e) {
            return new Random().nextInt((int) DATA_RANDOM);
        }

    }

    /**
     * 根據(jù)host name 取余
     *
     * @return
     */
    private long getHostId(String s, long max) {
        byte[] bytes = s.getBytes();
        long sums = 0;
        for (byte b : bytes) {
            sums += b;
        }
        return sums % (max + 1);
    }

    /**
     * 測(cè)試
     */
    public static void main(String[] args) {
        SnowflakeIdWorker idWorker = new SnowflakeIdWorker(0, 0);
        System.out.println(idWorker.nextId());
    }
}