基于Redis实现限流

限流尽可能在满足需求的情况下越简单越好！

1、基于Redsi的increment方法实现固定窗口限流

Redis的increment方法保证并发线程安全
窗口尽可能越小越好(太大可能某一小段时间就打满请求剩下的都拿不到令牌了)

这个原理其实就是用当前时间戳然后除窗口大小在这个窗口大小的时间内 key都一样

public class RedisRateLimiter {

复制代码

  private final StringRedisTemplate redisTemplate;
  // 命令前缀
  private final String key;

  private final int rate;

  private final int window;

  public RedisRateLimiter(StringRedisTemplate redisTemplate, String key, int rate,int window) {
      this.redisTemplate = redisTemplate;
      this.key = key;
      this.rate = rate;
      Assert.isTrue(window > 0 && window <= 60,"窗口只支持分钟内");
      this.window = window;
  }

  // 检查并获取令牌
  public boolean acquire() {
      String currentKey = key + "_" + (DateUtil.currentSeconds() / window);

      Long currentCount = redisTemplate.opsForValue().increment(currentKey);

      redisTemplate.expire(currentKey, window, TimeUnit.SECONDS);

      if (currentCount > rate){
          return false;
      }
      return true;
  }


  public void acquireSleep() {
      int count = 0;
      while (!acquire()){
          ThreadUtil.sleep(1,TimeUnit.SECONDS);
          count++;
          log.info("RedisRateLimiter[{}] try acquire sleep {}",key,count);
      }
  }

  public boolean acquireSleep(int waitSecond) {
      int count = 0;
      while (!acquire()){
          if (count >= waitSecond){
              return false;
          }
          ThreadUtil.sleep(1,TimeUnit.SECONDS);
          count++;
          log.info("RedisRateLimiter[{}] try acquire sleep {}",key,count);
      }
      return true;
  }

}

使用案例：

下面这个任务是实时请求评论和子评论接口，但是两个接口每分钟不能超过100，所以我们使用限流限制10秒不超过18即可也能满足需求。

复制代码

public class ScCommentRealTimeSyncTask  {
        private RedisRateLimiter rateLimiter;

        @PostConstruct
        public void init(){
            rateLimiter = new
                    RedisRateLimiter(stringRedisTemplate,KAOLA_COMMENT_RATE_KEY,16,10);
        }

        @Scheduled(fixedDelay = 3000)
        public void task(){
            // 请求接口1
            rateLimiter.acquireSleep();
            request1();
            
            //请求接口2
            rateLimiter.acquireSleep();
            request2();

        }


    }