The JavaFX way to do this is
File excelFile = new File("/path/to/excel/file");
getHostServices().showDocument(excelFile.toURI().toURL().toExternalForm());
getHostServices() is defined in Application, so if you want to do this in another class (a controller, for example), you will have to arrange for the other class to be able to access the host services.
E.g.
public class MyApp extends Application {
@Override
public void start(Stage primaryStage) throws Exception {
FXMLLoader loader = new FXMLLoader(...);
Parent root = loader.load();
MyController controller = loader.getController();
controller.setHostServices(getHostServices());
//... setup and show scene and stage...
}
}
With the obvious method in the controller and the code above suitably modified.