Reverse-engineer Source Code into UML Diagrams

http://java.dzone.com/articles/reverse-engineer-source-code-u

However, we don't have to keep making up stories anymore, since this article shows how easy and simple it is to include UML diagrams within your Javadoc and also keep them updated with every change in the source code repository. We can do these in less than a few minutes, and in a few simple steps.

Getting started with UmlGraph takes five steps:
Download the source code for UMlGraph.
Download and install Graphviz.
Make changes to your Ant build file.
Run the Ant target.
Add this target to your CI job.