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.