I suggest you pickup a good design book instead. Professional code usually does not explain important details such as "this is a factory pattern.". It also often contains loosely implemented patterns (if any) and custom requirements.
Design patterns are just far too complex to just figure it out on your own. It took the Gang of Four years to lay out the fundamentals. So its better to learn to do it correctly then see what others are doing.
Head first design patterns is a solid Java dp book.
Design and simplicity do not necessarily go hand in hand. Good design is heavily focused on proven use cases for a particular pattern. Not that the pattern is simple per-se, but that it works. Simplicity is as much an art as a science. It also requires a good understanding of the business requirements, framework and the customer. Keeping it simple takes years of practice. Even then time limits and reality plays a huge role in what's possible. Remember the triangle.