How to automatically refresh Cache using Google Guava?

Question

I am using Google Guava library for caching. For automatic cache refresh we can do as follows:

cache = CacheBuilder.newBuilder()               
                    .refreshAfterWrite(15, TimeUnit.MINUTES)
                    .maximumSize(100)
                    .build(....);

However, automatic refreshes are performed when the first stale request for an entry occurs.

Is there a way to refresh it automatically even though no requests came for cache data? Like for every 15 minutes the cache data should be pulled from Db and load it, no matter whether anybody called cache data or not.

Also, Guava's cache expiry time is for entire cache. Is it possible to expire cache values based on key? Like cache data with key "NOT_SO_FREQ_CHANGE_DATA" to expire for every 1 hour and data with key "FREQ_CHANGING_DATA" should expire for every 15 minutes?

Answer 1

Guava provides no way to refresh the cache in bulk, but you can schedule a periodic refresh yourself:

LoadingCache<K, V> cache = CacheBuilder.newBuilder()
        .refreshAfterWrite(15, TimeUnit.MINUTES)
        .maximumSize(100)
        .build(new MyCacheLoader());

for (K key : cache.asMap().keySet()) {
    cache.refresh(key);
}

But in that case you may want to override the CacheLoader.reload(K, V) method in MyCacheLoader so it performs asynchronously.

As for the second question, no, you cannot set a per-entry expiration in Guava.