Possible Web Framework to Use in Existing Application

I work for a medium sized company that has an application used by a few thousand people and is built primarily with HTML,Javascript, aspx, xml, xsl, and runs on IE 11. This application is proprietary and not designed in house but we have access to the code for possible modifications and its just sitting out there on the server(s). A new project has come down the pipline for an enhancement\adjustment to be made to a particular area of the application and I'm wondering what kind of web framework I could use to do this work. I am really just needing to call an enterprise service and get data back, display it, and that's about it, so its not incredibly hard. I am worried though about how to integrate it with the existing application.

I am not sure how this scenario would go:

User navigates to page A inputs data, I want that data to go to a controller or something I built, fetch info and send it back to page A. I was thinking of using Spring MVC but not sure. Any feed back or suggestions would be greatly appreciated! I know this question doesn't include code, so please don't hate me.

Thank you.