One very useful way to use this is to retrieve some data from the OPA session and add it to the velocity context for display on the screen, this is much easier than trying to navigate the API directly from velocity.
You could also put helper classes into the velocity context that the templates may find useful in generating the screens.
Thanks for the information. Can you please provide a working example on each of the above points so that I can experiment with it.
Please send me the working example to email@example.com?
I am not aware how to code a helper class and modifying the session data into onapplytemplateshandler.