It depends on the code. There are plenty of software packages which will reverse-engineer your code into a model and forward-engineer into a more standards-based one. A company, BluAge, based out of Belgium I believe has a good product worth looking at. Model-Driven Development is very much alive due to recent strides made in an agreement reached over using a flavor of UML as a modeling language. Hope this helps.
In addition to classic applications to generate UML models from Java code (Object Aid, maintainJ, Poseidon UML, UML Lab, Omondo...) you can use a great feature of Android Studio : http://tools.android.com/navigation-editor -> this can generate a kind of activity diagram (where activities is replaced by android activities).
The logic of mobile application is the same for web application or stand-stand alone application. The difference, if any, is in the presentation. Therefore, the same reverse engineering tools can be used to extract the logic in UML in MDE in an ADM effort.