How to proxy remote Java GUI?

Question

Java

Friends, push me in the right direction, please.
The essence of the problem: there is equipment that is serviced by proprietary software. This software does not have an API, but it does have a remote GUI. There is a need to write your own application that could affect the serving software.
I have little experience with Java, so I will not write the application in it.
So far, there is only one idea: to intercept the requests that the GUI sends, study them, and send the same ones. But through what protocol the GUI communicates with the server, I do not know.
The GUI itself is presented as a *.jnlp file, but as I understand it, this is just an instruction for building from other modules.

Answer 1

jnlp points to a jar file. Download it and run it locally on your computer.
If you really want to write your program directly, then decompile it)