The class was not seeing some imports from the same package, and some getters and setters for User.java were not written, so I wrote those and fixed the imports
FIX:: fixed packages
Everything now isn't in several subpackages in the Client, Common and Server package anymore, but straight in their respectable packages. Also fixed the package names
BUG FIX: fixed Client Application class not being able to see GetBean method
Don't really know how it got fixed, but resolving the import issues also fixed this bug.
EDIT::changed main class in build.gradle file to Client.Application
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I now only get a bug where the fxmlloader can't see the fxml files, and thus I can't start the application. I get the error message "location not set" although I used fxmlloader.setLocation.