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Seem like an example how to not to do this. I recommend to read "Java concurrency in practice", there is an example how caching proxy code should look like.

why not do it this way?

Interesting, but dynamic proxying has been around for quite some time, since 1.3, so I would hardy call this amazing.

This is a widely known technique called memoization.

http://en.wikipedia.org/wiki/Memoization

Just looked at the Java implementation link, and it is this same proxy method published five years ago.

http://www.onjava.com/pub/a/onjava/2003/08/20/memoization.html