With Modelio your code will be reversed (thanks to JavaDesigner )as a class, an operation, a parameter, a comment and that's all...
The body of the method will be reversed as the body of a UML comment owned by the operation (as depicted in my previous message) and not as some behavioural elements .
I never see an industrial tool reversing Java code in activity but if you know one's please tell me .
I've never seen any tool able to generate activity diagrams, however in my team, some people tested a tool that generate "dynamically" automatic sequence diagrams : www.architexa.com/learn-more/understand .
It does allow to browse quite effectively through an existing application, rather than publishing sets of pre-made diagrams.