is it possible to create a program that has both a web app component, and a desktop app component, in java

I want to create a program where same/similar data is submitted to many (thousands) of forms in an automated manner.

What I want to do is, the part of creating and showing web forms on screen (before user fills in captcha and form is submitted, are done by the web app, through a browser which is part of the desktop app. The response of each form submission is noted by the desktop app, which then invokes the web app to move forward to the next set of forms (to which data has to be submitted).

My questions-

1. Is it possible to do the above?
2. How does the desktop app talk to web app? Any examples you can give me on this. or any tutorials/guides? What I am thinking is, there is a simple button in the desktop app that indicates "success" or "failure" of a form submission- as per the button clicked by user, appropriate message (whether to proceed to next site in case of "success" or reload current site in case of "failure") is sent to web app by the desktop app. How do I actually implement this? How can the desktop app send messages to the web app that cannot be reverse engineered or hacked into?
3. Ideally I want that even if a hacker reverse开发者_如何学运维 engineers the desktop app, he should not be able to hack into the web app portion. (Since the web app portion does a crucial part of the work, so hacking the desktop app portion will not be any help in reverse engineering the whole application)...
4. Finally is it possible to do all of the above if I use Google App Engine for the web app portion?

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It's certainly possible. This is one of the roles that EJB was supposed to fill long, long ago. Today, the "enterprise" solution would probably be to do this with three parts: webapp, standalone GUI, and a ReST API to service both of them.