SnowFlakeId 分布式雪花id算法

package com.jn.baseservice.utils;

import com.jn.baseservice.common.Number;
import lombok.Getter;
import lombok.Setter;
import lombok.extern.log4j.Log4j2;
import org.apache.commons.lang3.StringUtils;
import org.springframework.context.ApplicationContext;

@Log4j2
@Getter
@Setter
public class SnowFlake {

    // 起始的时间戳
    private final static long START_TIMESTAMP = 1555894860007l;
    // 每一部分占用的位数，就三个
    private final static long SEQUENCE_BIT = 12;// 序列号占用的位数
    private final static long MACHINE_BIT = 5;// 机器标识占用的位数
    private final static long DATA_CENTER_BIT = 5;// 数据中心占用的位数
    // 每一部分最大值
    private final static long MAX_DATA_CENTER_NUM = 2 << DATA_CENTER_BIT - 1;
    private final static long MAX_MACHINE_NUM = 2 << MACHINE_BIT - 1;
    private final static long MAX_SEQUENCE = 2 << SEQUENCE_BIT - 1;
    // 每一部分向左的位移
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;
    private static long dataCenterId; // 数据中心 -- 分组按照 应用分组
    private static long machineId; // 机器标识
    private static long sequence = 0L; // 序列号
    private static long lastTimestamp = -1L;// 上一次时间戳

    public static boolean check;

    /**
     * 构造器
     *
     * @param dataCenterId
     * @param machineId
     */
    private static void SnowFlake(long dataCenterId, long machineId) {
        if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {
            throw new IllegalArgumentException("dataCenterId can't be greater than MAX_DATA_CENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        SnowFlake.dataCenterId = dataCenterId;
        SnowFlake.machineId = machineId;
    }

    /**
     * 初始化检查
     *
     * @param context
     */
    public synchronized static void initOrCheck(ApplicationContext context) {
        String applicationName = context.getId();
        long applicationHashCode = Math.abs(applicationName.hashCode() % MAX_DATA_CENTER_NUM);
        log.info("applicationName:{},dataCenterId:{}", applicationName, applicationHashCode);
        long ipHashCode = getIpCode();
        log.info("ipHashCode:{}", ipHashCode);
        SnowFlake(applicationHashCode, ipHashCode);
        check = true;
    }

    /**
     * 获取ip
     *
     * @return
     */
    public static long getIpCode() {
        String httpString = HttpUtil.getRequest("http://2019.ip138.com/ic.asp");
        log.info("获取ip回执：" + httpString);
        try {
            if (httpString != null) {
                httpString = httpString.substring(httpString.indexOf("[") + Number.ONE, httpString.indexOf("]"));
            }
        } catch (Exception e) {
            log.error("处理ip异常：", e);
        }
        log.info("处理后ip：" + httpString);
        long ipHashCode = StringUtils.isEmpty(httpString) ? System.currentTimeMillis() % MAX_MACHINE_NUM : Math.abs(httpString.hashCode() % MAX_MACHINE_NUM);
        return ipHashCode;
    }

    /**
     * 实际获取id
     *
     * @return
     */
    public synchronized static long nextId() {
        long currStamp = System.currentTimeMillis();
        if (currStamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStamp == lastTimestamp) {
            //if条件里表示当前调用和上一次调用落在了相同毫秒内，只能通过第三部分，序列号自增来判断为唯一，所以+1.
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大，只能等待下一个毫秒
            if (sequence == 0L) {
                currStamp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            //执行到这个分支的前提是currTimestamp > lastTimestamp，说明本次调用跟上次调用对比，已经不再同一个毫秒内了，这个时候序号可以重新回置0了。
            sequence = 0L;
        }

        lastTimestamp = currStamp;
        //就是用相对毫秒数、机器ID和自增序号拼接
        return (currStamp - START_TIMESTAMP) << TIMESTAMP_LEFT //时间戳部分
                | dataCenterId << DATA_CENTER_LEFT      //数据中心部分
                | machineId << MACHINE_LEFT            //机器标识部分
                | sequence;                            //序列号部分
    }

    /**
     * 获取时间戳
     *
     * @return
     */
    private static long getNextMill() {
        long mill = System.currentTimeMillis();
        while (mill <= lastTimestamp) {
            mill = System.currentTimeMillis();
        }
        return mill;
    }

}

//获取雪花id
public static long getSnowFlakeId() {
        if (!SnowFlake.check) {
            SnowFlake.initOrCheck(SpringConfigTool.getContext());
        }
        return SnowFlake.nextId();
    }