Hank Gay Hank Gay - 5 months ago 10x
Java Question

How would you implement an LRU cache in Java?

Please don't say EHCache or OSCache, etc. Assume for purposes of this question that I want to implement my own using just the SDK (learning by doing). Given that the cache will be used in a multithreaded environment, which datastructures would you use? I've already implemented one using LinkedHashMap and Collections#synchronizedMap, but I'm curious if any of the new concurrent collections would be better candidates.

UPDATE: I was just reading through Yegge's latest when I found this nugget:

If you need constant-time access and want to maintain the insertion order, you can't do better than a LinkedHashMap, a truly wonderful data structure. The only way it could possibly be more wonderful is if there were a concurrent version. But alas.

I was thinking almost exactly the same thing before I went with the
implementation I mentioned above. Nice to know I hadn't just overlooked something.

Based on the answers so far, it sounds like my best bet for a highly concurrent LRU would be to extend ConcurrentHashMap using some of the same logic that


If I were doing this again from scratch today, I'd use Guava's CacheBuilder.