spritesheet.loadFromFile(Paths.get("res/spritesheet.png"));
This means that you are reading the texture from the filesystem, not the classpath.
In your released version, you would need a directory called "res" with the file in it, it won't work in the jar.
You need to load it from the classpath / jar, using the
loadFromStream method using the path to the resource (look that up, easy to find information
).
side note: is jSFML still being worked on?
Ouch.
At the moment, no. Most SFML 2.2 changes had been incorporated, but I never made an official build because I had no environment set up. I completely lost track of what's going on when 2.3 was released, because I have no use for SFML myself at the moment.
I also said goodbye to Java after quitting a job in summer, so the situation is not exactly great for JSFML.
If somebody's willing to take over, that'd probably be best for the project. For now, I can only help with what's there.