问JavaFX警报不是在新窗口中打开，而是在新选项卡中打开

EN

public class MainViewController {

    @FXML
    private void handleQuitButtonAction(ActionEvent event) {
        System.exit(0);
    }

    @FXML
    private void handleImportButtonAction(ActionEvent event) {
        FileChooser fileChooser = new FileChooser();
        fileChooser.setTitle("Select the file to import");
        File file = fileChooser.showOpenDialog(new Stage());
        Alert alert;
        if (FileAccess.importFile(file)) {
            alert = new Alert(AlertType.INFORMATION);
            alert.setTitle("Success!");
            alert.setHeaderText("Congrats!");
            alert.setContentText("Successfully imported data from the chosen file!");
        } else {
            alert = new Alert(AlertType.ERROR);
            alert.setTitle("Error!");
            alert.setHeaderText("Sorry...");
            alert.setContentText("Something wrong with the import, please try again.");
        }
        alert.showAndWait();

        // Refresh Scroll List
    }

    @FXML
    private void handleExportButtonAction(ActionEvent event) {
    }
}

public class MainApp extends Application {

    private Stage primaryStage;
    private BorderPane mainView;

    @Override
    public void start(Stage primaryStage) {
        this.primaryStage = primaryStage;
        this.primaryStage.setTitle("Main System");
        showMainView();
    }

    private void showMainView() {
        try {
            // Load Main View from FXML file.
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(MainApp.class.getResource("view/MainView.fxml"));
            mainView = (BorderPane) loader.load();

            // Show the scene containing the root layout.
            Scene scene = new Scene(mainView);
            primaryStage.setScene(scene);
            primaryStage.show();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public Stage getPrimaryStage() {
        return primaryStage;
    }

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

public class FileAccess {

    public static boolean importFile(File file) {
        return false;
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.geometry.Insets?>
  <?import javafx.scene.control.Button?>
    <?import javafx.scene.control.ButtonBar?>
      <?import javafx.scene.control.ScrollPane?>
        <?import javafx.scene.effect.DropShadow?>
          <?import javafx.scene.layout.BorderPane?>

            <BorderPane prefHeight="600.0" prefWidth="800.0" xmlns="http://javafx.com/javafx/8.0.171" xmlns:fx="http://javafx.com/fxml/1" fx:controller="view.MainViewController">
              <center>
                <ScrollPane prefWidth="800.0" BorderPane.alignment="CENTER" />
              </center>
              <top>
                <ButtonBar prefHeight="40.0" prefWidth="200.0" BorderPane.alignment="CENTER">
                  <buttons>
                    <Button focusTraversable="false" mnemonicParsing="false" onAction="#handleImportButtonAction" text="Import" ButtonBar.buttonData="LEFT" />
                    <Button focusTraversable="false" mnemonicParsing="false" onAction="#handleExportButtonAction" text="Export" ButtonBar.buttonData="LEFT" />
                    <Button focusTraversable="false" mnemonicParsing="false" onAction="#handleQuitButtonAction" text="Quit Program" ButtonBar.buttonData="RIGHT" />
                  </buttons>
                  <effect>
                    <DropShadow />
                  </effect>
                  <BorderPane.margin>
                    <Insets left="10.0" right="10.0" />
                  </BorderPane.margin>
                </ButtonBar>
              </top>
            </BorderPane>