cache = CacheBuilder.newBuilder()
                .maximumSize(fessConfig.getSuggestPopularWordCacheSizeAsInteger().longValue())
                .expireAfterWrite(fessConfig.getSuggestPopularWordCacheExpireAsInteger().longValue(), TimeUnit.MINUTES)
                .build();
    }

    /**
     * Retrieves a list of popular words based on the specified search parameters.

     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     * @throws NumberFormatException When the property is not integer.
     */
    Integer getSuggestPopularWordCacheExpireAsInteger();

    /**
     * Get the value for the key 'suggest.search.log.permissions'. <br>
     * The value is, e.g. {user}guest,{role}guest <br>
     * comment: Permissions for suggestion search log.