code: public static Single<Boolean> exists(CacheConfigBean cacheConfigBean, String cacheKey) {
          return SingleRxXian.call(CacheService.CACHE_SERVICE, "cacheExists", new JSONObject() {{
              put("cacheConfig", cacheConfigBean);
              put("key", cacheKey);
          }}).map(unitResponse -> {
              unitResponse.throwExceptionIfNotSuccess();
              return (boolean) unitResponse.getData();
          });
      }
docs: check whether the key exists.
  
  @param cacheConfigBean the cache data source.
  @param cacheKey        the key of the key
  @return true if exists otherwise false.