@Override
    public Mono<Boolean> isExist(final String key) {
        return this.redisTemplate.hasKey(key);
    }
Check the cache is existed or not.
@param key the cache key
@return true exist
shenyu-plugin/shenyu-plugin-cache/shenyu-plugin-cache-redis/src/main/java/org/apache/shenyu/plugin/cache/redis/RedisCache.java