JCache (JSR 107) Under the Hood

Recently I’ve been dealing with caching at work, and wrote a web service of my own that needed some caching too.  I took this opportunity to look into JCache (JSR 107).  There are some good caches out there that implement this standard, but because I wanted something light weight for my web service and I really wanted to get familiar with the standard I decided to go ahead and write a trivial implementation myself.  What follows are some of my observations about the standard from both an implementer’s and a user’s perspectives.

As a User

The API is very straight forward, especially for the general use cases. It is somewhere between a Map and a ConcurrentHashMap, with some of the more powerful conditional methods like getAnd*, compute and replace variations. The cache set up is sane too, although some of the more elaborate features can get a little involved to get going.


  • Allows for swapping various implementations at will.
  • Sane API with good feature set. Easy to use.


  • More involved setups start requiring a fair bit of boilerplate code, rife with Factory and Listener subclassing. Hopefully the next round of the spec will include some JDK 8+ functional goodies and clean that up.
  • Some of the bulk operations APIs don’t seem particularly optimized. For example there was no intuitive way to prime the cache except by passing in a specific key set.

As an Implementer

Implementing a minimal set, i.e. useful but not compliant, was straight forward. Once I moved on the the more peripheral features things got a little less pleasant.  It feels like the core API was given a lot more thought then some of the lesser features.


  • Basic API is clean and logical. Documentation covers semantics pretty well. There’s a reference implementation to double check things on.
  • Get a useful product by implementing a clear subset.


  • Added it’s own Key/Value interface rather then us Map.Entry. Exact signature match, but distinct. The API’s include uses of the standard Java collections but but the cache requires a unique Entry classes. Forces unnecessary conversions.
  • Really suffers from it’s timing prior to JDK 1.8.  Every consumer function has a distinct non-functional signature.
  • Has a weak “unwrap” pattern to cast types that really doesn’t help things much.


I’ll definitely gravitate to this API for caching.  It’s clean, powerful enough, and has a good selection of implementations.  I’m hoping that as the spec evolves and incorporates JDK 8+ features most of the rough edges smooth away.

My Implementation

If you are curious about my partial implementation it can be found here on github.

So you want to write a RESTful server in Java…

For work I’ve been helping some folks with a demo Android app. They needed a backend to test against and so whipping up a servlet was suggested.  A couple hours work…. if you’ve done it a bunch.  So I hacked up a skeleton and promised some references. I thought I do it here and share. These are some of my favorite ingredients for throwing together a servlet backend.