缓存击穿、雪崩、穿透三大Redis问题总结

当缓存和数据库都没有查询到请求时，就往缓存中存入null，并且设置ttl

热点key一般都会提前写入缓存，所以不用担心缓存穿透的问题

public Shop queryWithMutex(Long id) {
    String key = CACHE_SHOP_KEY + id;
    //从Redis中查询缓存
    String shopString = stringRedisTemplate.opsForValue().get(key);
    //判断缓存是否存在
    if (StrUtil.isNotBlank(shopString)) {
        //请求命中，直接返回
        //先把JSON转化为对象

        return JSONUtil.toBean(shopString, Shop.class);

    }
    //解决了缓存穿透
    if (shopString == "") {

        return null;
    }

    //缓存未命中
    //尝试获取锁
    String lockeKey = LOCK_SHOP_KEY + id;
    Shop shop = null;
    try {
        boolean isLock = getLock(lockeKey);
        if (!isLock) {
            //获取锁失败,休眠一段时间后重新获取
            Thread.sleep(50);
            queryWithMutex(id);
        }
        //获取锁成功,查询数据库重建缓存
        shop = getById(id);
        //判断商铺是否存在
        if (shop == null) {
            //解决缓存穿透,缓存null
            stringRedisTemplate.opsForValue().set(key, "", CACHE_NULL_TTL, TimeUnit.MINUTES);
            //不存在
            return null;

        }
        //存在，将数据缓存到Redis
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(shop), CACHE_SHOP_TTL, TimeUnit.MINUTES);


    } catch (InterruptedException e) {
        throw new RuntimeException();

    } finally {
        //释放互斥锁
        deleteLock(lockeKey);
    }

    return shop;

}

public Shop queryLogicalExpiration(Long id) {
        String key = CACHE_SHOP_KEY + id;
        //从Redis中查询缓存
        String shopString = stringRedisTemplate.opsForValue().get(key);
        RedisDate redisDate = JSONUtil.toBean(shopString, RedisDate.class);
        LocalDateTime expiration = redisDate.getExpiration();
        Shop shop = JSONUtil.toBean((JSONObject) redisDate.getData(), Shop.class);
        //判断缓存是否存在
        if (StrUtil.isNotBlank(shopString)) {
            //未命中
            return null;

        }
        //判断缓存是否过期
        if (expiration.isAfter(LocalDateTime.now())) {
            //过期直接返回旧数据
            return shop;
        }
        //未过期,尝试获取锁
        boolean lockBoolean = getLock(key);
        //成功
        if (lockBoolean) {
            //开启独立线程,更新店铺信息

            EXECUTOR_SERVICE.submit(() -> {

                try {
                    this.insertLogical(id, 20L);

                } catch (Exception e) {
                    throw new RuntimeException();
                } finally {
                    deleteLock(key);
                }

            });

        }
        //不成功返回旧数据
        return shop;
    }