框架篇：分布式全局唯一ID

CREATE TABLE FLIGHT_ORDER (
    id int(11) unsigned NOT NULL auto_increment, #自增ID
    PRIMARY KEY (id),
) ENGINE=innodb;

 @Autowired
 private StringRedisTemplate stringRedisTemplate;
 private static final String ID_KEY = "id_good_order";
 public Long incrementId(){
     return stringRedisTemplate.opsForValue().increment(ID_KEY);
 }

//KEY_NAME 是 hash结构对应的Key,FIELD_NAME 是hash结构的字段，INCR_BY_NUMBER是增量值
redis 127.0.0.1:6379> HINCRBY KEY_NAME FIELD_NAME INCR_BY_NUMBER 

<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-framework</artifactId>
    <version>4.2.0</version>
</dependency>
<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-recipes</artifactId>
    <version>4.2.0</version>
</dependency>

RetryPolicy retryPolicy = new ExponentialBackoffRetry(500, 3);
CuratorFramework client = CuratorFrameworkFactory.builder()
      .connectString("localhost:2181")
      .connectionTimeoutMs(5000)
      .sessionTimeoutMs(5000)
      .retryPolicy(retryPolicy)
      .build();
client.start();  
String sequenceName = "root/sequence/distributedId";
DistributedAtomicLong  distAtomicLong = new DistributedAtomicLong(client, sequenceName, retryPolicy);
//使用DistributedAtomicLong生成自增序列
public Long sequence() throws Exception {
    AtomicValue<Long> sequence = this.distAtomicLong.increment();
    if (sequence.succeeded()) {
        return sequence.postValue();
    } else {
        return null;
    }
}

String uuid = UUID.randomUUID().toString().replaceAll("-","");

//Twitter的SnowFlake算法,使用SnowFlake算法生成一个整数
public class SnowFlakeShortUrl {
    //起始的时间戳
    static long START_TIMESTAMP = 1624698370256L;
    //每一部分占用的位数
    static long SEQUENCE_BIT = 12;   //序列号占用的位数
    static long MACHINE_BIT = 5;     //机器标识占用的位数
    static long DATA_CENTER_BIT = 5; //数据中心占用的位数
    //每一部分的最大值
    static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
    static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    static long MAX_DATA_CENTER_NUM = -1L ^ (-1L << DATA_CENTER_BIT);
    //每一部分向左的位移
    static long MACHINE_LEFT = SEQUENCE_BIT;
    static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;
    //dataCenterId + machineId 等于10bit工作机器ID
    private long dataCenterId;  //数据中心
    private long machineId;     //机器标识
    private volatile long sequence = 0L; //序列号
    private volatile long lastTimeStamp = -1L;  //上一次时间戳
    private volatile long l currTimeStamp = -1L; //当前时间戳
    
    private long getNextMill(){
        long mill = System.currentTimeMillis();
        while (mill <= lastTimeStamp) mill = System.currentTimeMillis();
        return mill;
    }
    //根据指定的数据中心ID和机器标志ID生成指定的序列号
    public SnowFlakeShortUrl(long dataCenterId, long machineId){
        Assert.isTrue(dataCenterId >=0 && dataCenterId <= MAX_DATA_CENTER_NUM,"dataCenterId is illegal!");
        Assert.isTrue(machineId >= 0 || machineId <= MAX_MACHINE_NUM,"machineId is illegal!");
        this.dataCenterId = dataCenterId;
        this.machineId = machineId;
    }
    //生成下一个ID
    public synchronized long nextId(){
        currTimeStamp = System.currentTimeMillis();
        Assert.isTrue(currTimeStamp >= lastTimeStamp,"Clock moved backwards");
        if (currTimeStamp == lastTimeStamp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0L) { //同一毫秒的序列数已经达到最大,获取下一个毫秒
                currTimeStamp = getNextMill();
            }
        } else { 
            sequence = 0L; //不同毫秒内，序列号置为0
        }
        lastTimeStamp = currTimeStamp;
        return (currTimeStamp - 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
    }
    
    public static void main(String[] args){
        SnowFlakeShortUrl snowFlake = new SnowFlakeShortUrl(10, 4);
        for (int i = 0; i < (1 << 12); i++) {
            //10进制
            System.out.println(snowFlake.nextId());
        }
    }
}