使用场景

用户登录后，需要把用户信息(一般是session)保存到redis中并设置过期时间

1.pom文件中引入springboot-redis依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

2.application.properties中加入redis数据库连接信息

#redis 配置
# Redis数据库索引（默认为0）
spring.redis.database=0
# Redis服务器地址
spring.redis.host=127.0.0.1
# Redis服务器连接端口
spring.redis.port=6379 

3.controller中注入雪花算法实例和redisTemplate实例

@Resource
private SnowFlake snowFlake;

@Resource
private RedisTemplate redisTemplate;

4.controller中使用雪花算法生成token并放入redis中并打印token日志信息

@PostMapping("/login")
public CommonResp login(@Valid @RequestBody UserLoginReq req) {
    req.setPassword(DigestUtils.md5DigestAsHex(req.getPassword().getBytes()));
    CommonResp<UserLoginResp> resp = new CommonResp<>();
    UserLoginResp userLoginResp = userService.login(req);

    String  token = snowFlake.nextId()+"";
    LOG.info("生成单点登录token：{}，并放入redis中", token);
    userLoginResp.setToken(token);
    redisTemplate.opsForValue().set(token, JSONObject.toJSONString(userLoginResp), 3600 * 24, TimeUnit.SECONDS);
    resp.setContent(userLoginResp);
    return resp;
}

关于redis的注意事项：

1.redisTemplate.opsForValue().set()是往redis设置一个k-v，k为token，value就是用户信息,后面的是过期时间和时间格式

2.value值必是序列化过的否则会报错，所以需要JSONObject.toJSONString把用户信息变成string类型的字段串

雪花算法

1.添加utils包下的SnowFlake文件

package com.futureport.wiki.utils;

import org.springframework.stereotype.Component;

import java.text.ParseException;

/**
 * Twitter的分布式自增ID雪花算法
 **/
@Component
public class SnowFlake {

    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1609459200000L; // 2021-01-01 00:00:00

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 7; //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 = 1;  //数据中心
    private long machineId = 1;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳

    public SnowFlake() {
    }

    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) throws ParseException {
        // 时间戳
        // System.out.println(System.currentTimeMillis());
        // System.out.println(new Date().getTime());
        //
        // String dateTime = "2021-01-01 08:00:00";
        // SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        // System.out.println(sdf.parse(dateTime).getTime());

        SnowFlake snowFlake = new SnowFlake(1, 1);

        long start = System.currentTimeMillis();
        for (int i = 0; i < 10; i++) {
            System.out.println(snowFlake.nextId());
            System.out.println(System.currentTimeMillis() - start);
        }
    }
}