您不应该关注X，而应该关注像这样的通用关闭请求：

primaryStage.setOnCloseRequest(new EventHandler<WindowEvent>() {
    @Override
    public void handle(WindowEvent event) {

        // consume event
        event.consume();

        // show close dialog
        Alert alert = new Alert(AlertType.CONFIRMATION);
        alert.setTitle("Close Confirmation");
        alert.setHeaderText("Do you really want to quit?");
        alert.initOwner( primaryStage);

        Optional<ButtonType> result = alert.showAndWait();
        if (result.get() == ButtonType.OK){
            Platform.exit();
        }
    }
});