一种简单的ID生成策略: Mysql表生成全局唯一ID的实

CREATE TABLE `guid` (
 `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
 `stub` char(1) NOT NULL DEFAULT '' COMMENT '桩字段,占坑的',
 PRIMARY KEY (`id`),
 UNIQUE KEY `uk_stub` (`stub`) -- 将 stub 设为唯一索引
) ENGINE=MyISAM AUTO_INCREMENT=1000000000 DEFAULT CHARSET=utf8;

@Mapper
public interface GuidMapper {


 /**获取全局唯一ID
  * @return
  */
 // replace into afs_guid(stub) values('a');
 // select last_insert_id();
 @Insert("REPLACE INTO guid (stub) VALUES('a')")
 @SelectKey(statement = {"SELECT LAST_INSERT_ID()"}, keyProperty = "guidHolder.id", before = false, resultType = long.class)
 int getGuid( @Param("guidHolder") GuidHolder guidHolder);

 @Data
 public static class GuidHolder{
  private long id;
  private String stub;
 }

 GuidMapper.GuidHolder guidHolder = new GuidMapper.GuidHolder();
 int i = guidMapper.getGuid(guidHolder);
 long     guid   = guidHolder.getId();
 // guid 就是返回的ID

/**
 * twitter的snowflake算法 -- java实现
 * 
 * @author beyond
 * @date 2016/11/26
 */
public class SnowFlake {

 /**
  * 起始的时间戳
  */
 private final static long START_STMP = 1480166465631L;

 /**
  * 每一部分占用的位数
  */
 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 DATACENTER_BIT = 5;//数据中心占用的位数

 /**
  * 每一部分的最大值
  */
 private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
 private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
 private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

 /**
  * 每一部分向左的位移
  */
 private final static long MACHINE_LEFT = SEQUENCE_BIT;
 private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
 private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

 private long datacenterId; //数据中心
 private long machineId;  //机器标识
 private long sequence = 0L; //序列号
 private long lastStmp = -1L;//上一次时间戳

 public SnowFlake(long datacenterId, long machineId) {
  if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
   throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_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");
  }
  this.datacenterId = datacenterId;
  this.machineId = machineId;
 }

 /**
  * 产生下一个ID
  *
  * @return
  */
 public synchronized long nextId() {
  long currStmp = getNewstmp();
  if (currStmp < lastStmp) {
   throw new RuntimeException("Clock moved backwards. Refusing to generate id");
  }

  if (currStmp == lastStmp) {
   //相同毫秒内，序列号自增
   sequence = (sequence + 1) & MAX_SEQUENCE;
   //同一毫秒的序列数已经达到最大
   if (sequence == 0L) {
    currStmp = getNextMill();
   }
  } else {
   //不同毫秒内，序列号置为0
   sequence = 0L;
  }

  lastStmp = currStmp;

  return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
    | datacenterId << DATACENTER_LEFT  //数据中心部分
    | machineId << MACHINE_LEFT    //机器标识部分
    | sequence;        //序列号部分
 }

 private long getNextMill() {
  long mill = getNewstmp();
  while (mill <= lastStmp) {
   mill = getNewstmp();
  }
  return mill;
 }

 private long getNewstmp() {
  return System.currentTimeMillis();
 }

 public static void main(String[] args) {
  SnowFlake snowFlake = new SnowFlake(2, 3);

  for (int i = 0; i < (1 << 12); i++) {
   System.out.println(snowFlake.nextId());
  }

 }
}

<dependency>
 <groupId>cn.hutool</groupId>
 <artifactId>hutool-all</artifactId>
 <version>5.3.1</version>
</dependency>

/**
 * 雪花算法
 *
 * @author: 陌溪
 * @create: 2020-04-18-11:08
 */
public class SnowFlakeDemo {
 private long workerId = 0;
 private long datacenterId = 1;
 private Snowflake snowFlake = IdUtil.createSnowflake(workerId, datacenterId);

 @PostConstruct
 public void init() {
  try {
   // 将网络ip转换成long
   workerId = NetUtil.ipv4ToLong(NetUtil.getLocalhostStr());
  } catch (Exception e) {
   e.printStackTrace();
  }
 }

 /**
  * 获取雪花ID
  * @return
  */
 public synchronized long snowflakeId() {
  return this.snowFlake.nextId();
 }

 public synchronized long snowflakeId(long workerId, long datacenterId) {
  Snowflake snowflake = IdUtil.createSnowflake(workerId, datacenterId);
  return snowflake.nextId();
 }

 public static void main(String[] args) {
  SnowFlakeDemo snowFlakeDemo = new SnowFlakeDemo();
  for (int i = 0; i < 20; i++) {
   new Thread(() -> {
    System.out.println(snowFlakeDemo.snowflakeId());
   }, String.valueOf(i)).start();
  }
 }
}

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