I have always been quite impressed with the Spring framework and its code. It’s not always the easiest thing to navigate (very deep hierarchies and some fairly advanced java concepts), but it’s always consistent, documented and well written. The deep hierarchies can be a pain to follow, but it is also what makes Spring extensible and customizable.
The sourcecode has been analyzed here and here, and the results are good. It pays to keep a close eye on some metrics.
We’re trying to do the same thing now and use the Maven reports as well as XRadar reports. It’s too early to draw any conclusions but I belive it will improve the quality of our code a lot.