Any Java caches that can limit memory usage of in-memory cache, not just instance count?

Question

I am looking for a simple in-memory (and in-process) cache for short-term caching of query data (but short-term meaning beyond request/response, i.e. session boundary). EhCache

Answer 1

If you cannot make any estimations - write a cache eviction policy which flushes based on the JVM heap size (polled from System) or triggered by a finalize()-call from an orphaned object (on GC).