close fxml window by code, javafx

I need to close the current fxml window by code in the controller

I know stage.close() or stage.hide() do this in fx

how to implement this in fxml? I tried

private void on_btnClose_clicked(ActionEvent actionEvent) {
        Parent root = FXMLLoader.load(getClass().getResource("currentWindow.fxml"));    
        Scene scene = new Scene(root);

        Stage stage = new Stage();            
        stage.setScene(scene);
        stage.show();
}

but it doesn't work!

All help will be greatly appreciated. Thanks!

1. give your close button an fx:id, if you haven't yet: <Button fx:id="closeButton" onAction="#closeButtonAction">

2. In your controller class:

   @FXML private javafx.scene.control.Button closeButton;
   
   @FXML
   private void closeButtonAction(){
       // get a handle to the stage
       Stage stage = (Stage) closeButton.getScene().getWindow();
       // do what you have to do
       stage.close();
   }
   

If you have a window which extends javafx.application.Application; you can use the following method. (This will close the whole application, not just the window. I misinterpreted the OP, thanks to the commenters for pointing it out).

Platform.exit();

Example:

public class MainGUI extends Application {
.........

Button exitButton = new Button("Exit");
exitButton.setOnAction(new ExitButtonListener());
.........

public class ExitButtonListener implements EventHandler<ActionEvent> {

  @Override
  public void handle(ActionEvent arg0) {
    Platform.exit();
  }
}

Edit for the beauty of Java 8:

 public class MainGUI extends Application {
    .........

    Button exitButton = new Button("Exit");
    exitButton.setOnAction(actionEvent -> Platform.exit());
 }