Using REST with .jsp

Question

I got assigned to update our site a bit today using REST. Basically the goal of the update is to enable our "New User Sign Up form" to send the data to our database which it already days. However, we also need that same data to go to a email marketing service's database. I was provided with the username, password, api key, as well as the actual url to the server.

I have been searching the web for tutorials, but so far I have had no luck in finding one that utilizes REST with .jsp.

Edit: Basically what I have so far is a "new user registration" form on my site. Once you fill it out and click "register", the data is then stored in our database. We are using emailvision to handle our newsletter delivery, and I was asked to set up the registration form to send the data (via emailvision's API) to their database as well as to our's. The page is currently a .jsp page. I have never done anything with api's either.