Looking for simple Java in-memory cache

Question

I'm looking for a simple Java in-memory cache that has good concurrency (so LinkedHashMap isn't good enough), and which can be serialized to disk periodically.

One feature I need, but which has proved hard to find, is a way to "peek" at an object. By this I mean retrieve an object from the cache without causing the cache to hold on to the object any longer than it otherwise would have.

Update: An additional requirement I neglected to mention is that I need to be able to modify the cached objects (they contain float arrays) in-place.

Can anyone provide any recommendations?

user_7671 · Answer

Ehcache is a pretty good solution for this and has a way to peek (getQuiet() is the method) such that it doesn't update the idle timestamp. Internally, Ehcache is implemented with a set of maps, kind of like ConcurrentHashMap, so it has similar kinds of concurrency benefits.

Evan_6277 · Answer

If you're needing something simple, would this fit the bill?

Map myCache = Collections.synchronizedMap(new WeakHashMap());

It wont save to disk, but you said you wanted simple...

Links:

(As Adam commented, synchronising a map has a performance hit. Not saying the idea doesn't have hairs on it, but would suffice as a quick and dirty solution.)

TofuBeer_65868 · Answer

How about this: https://commons.apache.org/proper/commons-jcs/ (updated to new address, as JCS is now in Apache Commons)

Stephen_37193 · Answer

Try Ehcache? It allows you to plug in your own caching expiry algorithms so you could control your peek functionality.

You can serialize to disk, database, across a cluster etc...

Looking for simple Java in-memory cache

9 Answers