Google Guava cache auto remove value of Optional.absent()

Question

Is it possible to auto evict the record with value Optional.absent()? In some applications the Optional.absent() may not be the value for some keys. For example, if an application contains http calls where the key can be some string and the value is response returned from the http call, the http call can return some invalid values (for example null) because of network issues or authentication failures, then the invalid can be saved as Optional.absent() with the key in cache. At a later point, if the network and authentication problems are fixed, the key->invalidValue still remains in the cache. What is the best to fix this problem?

Answer 1

For example, if an application contains http calls where the key can be some string and the value is response returned from the http call, the http call can return some invalid values (for example null) because of network issues or authentication failures

If possible, I would change this behavior to throw an exception when the request fails or the response is invalid - that's what exceptions are for. See Effective Java: Item 57 for more.

then the invalid can be saved as Optional.absent() with the key in cache. At a later point, if the network and authentication problems are fixed, the key->invalidValue still remains in the cache. What is the best to fix this problem?

Is there a reason you need to save the invalid result in the cache? If you don't care about the absent case and simply want it excluded from the cache the easiest option would be to just not cache it in the first place. Throwing an exception on bad results would make that easy.

If you do need to keep the invalid results in the cache temporarily you can clear them once you're ready with a simple for loop:

ConcurrentMap<K, V> cacheAsMap = cache.asMap();
for (Entry<K, V> e : cacheAsMap .entrySet()) {
  if (!e.getValue().isPresent()) {
    cacheAsMap.remove(e.getKey(), e.getValue());
  }
}

By using ConcurrentMap.remove() you avoid a possible race condition where the entry is updated after e.getValue().isPresent() is called but before the entry is actually invalidated.