Integration of web flow in an application using velocity template

We have an application here where we want use web flow . In the application we currently
use velocity template for creating html string , we use tridion xml for keeping page content.
By using this xml and passing the page content through velocity template we get html string
which is then flushed into the response stream.For each page there is a controller.

Problem : in web-flow.xml how we can controller form where the page will get rendered and for a particular event
from the generated page we can select one of the transition in the web-flow.xml to call another controller.
In this we want to maintain the flow

Please suggest