如何在控制器类中引用Stage？

主类

public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {
            Parent root = FXMLLoader.load(getClass().getResource("/application/Main.fxml"));
            Scene scene = new Scene(root);
            scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
            primaryStage.setScene(scene);
            primaryStage.show();
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        launch(args);
    }
}

MainController.class

    public class MainController implements Initializable {

    @FXML private MediaView mv;
    private MediaPlayer mp;
    private Media me;

    @FXML Slider volumeSlider;

    DoubleProperty width;
    DoubleProperty height;

    Stage stage;

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        // TODO Auto-generated method stub
        String path = new File("src/media/my.mp4").getAbsolutePath();
        me = new Media(new File(path).toURI().toString());
        mp = new MediaPlayer(me);
        mv.setMediaPlayer(mp);
        //mp.setAutoPlay(true);

        stage = (Stage) mv.getScene().getWindow();  // Error occured

        width = mv.fitWidthProperty();
        height = mv.fitHeightProperty();
        width.bind(Bindings.selectDouble(mv.sceneProperty(), "width"));
        height.bind(Bindings.selectDouble(mv.sceneProperty(), "height"));

        volumeSlider.setValue(mp.getVolume() * 100);
        volumeSlider.valueProperty().addListener(new InvalidationListener() {

            @Override
            public void invalidated(Observable observable) {
                // TODO Auto-generated method stub
                mp.setVolume(volumeSlider.getValue() / 100);
            }
        });
    }

    public void play(ActionEvent event){
        mp.play();
        mp.setRate(1);
    }
    public void pause(ActionEvent event){
        mp.pause();
    }
    public void fast(ActionEvent event){
        mp.setRate(2);
    }
    public void slow(ActionEvent event){
        mp.setRate(.5);
    }
    public void reload(ActionEvent event){
        mp.seek(mp.getStartTime());
        mp.play();
    }
    public void start(ActionEvent event){
        mp.seek(mp.getStartTime());
        mp.stop();
    }
    public void last(ActionEvent event){
        mp.seek(mp.getTotalDuration());
        mp.stop();
    }
    public void fullScreen(ActionEvent event){

    }
}

错误

javafx.fxml.LoadException: 
/C:/Users/SOONMYUN/workspace/MediaPlayer/bin/application/Main.fxml

    at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3214)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
    at application.Main.start(Main.java:17)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
    at application.MainController.initialize(MainController.java:44)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
    ... 17 more

我想将舞台从Main类升级到Controller类，但失败了。

因为我应该在Controller类中使用setFullScreen函数。