HashMap with weak values

Question

I\'m implementing a cache for Objects stored persistently. The idea is:

• Method getObjectFromPersistence(long id); ///Takes about 3 seconds
• M

Answer 1

A WeakReference is added to its ReferenceQueue supplied at the construction time when its reference is collected.

You could poll the ReferenceQueue whenever you access the cache, and hold a HashMap,Long> to know which entry to remove if a reference is found in the queue.

Alternatively, if the cache is not frequently used, you can watch the queue in a separate thread.