Historically we always built the CacheKey with the id value directly. Nothing has changed there. There are pros and cons to that.

But it sounds like you need for Ehcache to store the disassembled version of the id value, at least in the case of overflowing to disk. You have access to the Type, and so you have access to perform the disassemble call in the Ehcache RegionFactory if that is what works better.