Load fxml as background process - Javafx

Question

My initial fxml(say home.fxml) has a lot of functionalities, hence it takes a lot of time to load completely. So to avoid the time gap between program start and

Answer 1

Use a Task. You need to arrange to create the scene and update the stage on the FX Application Thread. The cleanest way is to use a Task:

Task loadTask = new Task() {
    @Override
    public Parent call() throws IOException {
        FXMLLoader loader = new FXMLLoader();
        Parent root = loader.load(getClass().getResource("/uatreportgeneration/fxml/Home.fxml"));
        return root ;
    }
};

loadTask.setOnSucceeded(e -> {
    Scene scene = new Scene(loadTask.getValue());

    mainStage.setScene(scene);
    mainStage.show();
    stage.hide();
    System.out.println("Stage showing");
    // Get current screen of the stage
    ObservableList screens = Screen.getScreensForRectangle(new Rectangle2D(mainStage.getX(), mainStage.getY(), mainStage.getWidth(), mainStage.getHeight()));
    // Change stage properties
    Rectangle2D bounds = screens.get(0).getVisualBounds();
    mainStage.setX(bounds.getMinX());
    mainStage.setY(bounds.getMinY());
    mainStage.setWidth(bounds.getWidth());
    mainStage.setHeight(bounds.getHeight());
    System.out.println("thread complete");
});

loadTask.setOnFailed(e -> loadTask.getException().printStackTrace());

Thread thread = new Thread(loadTask);
thread.start();

---

Here is a SSCCE using this technique:

main.fxml:

MainController (uses the Task approach shown above):

import java.io.IOException;

import javafx.concurrent.Task;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.stage.Stage;

public class MainController {
    @FXML
    private Button button ;
    @FXML
    private void showWindow() {
        Task loadTask = new Task() {
            @Override
            public Parent call() throws IOException, InterruptedException {

                // simulate long-loading process:
                Thread.sleep(5000);

                FXMLLoader loader = new FXMLLoader(getClass().getResource("test.fxml"));
                Parent root = loader.load();
                return root ;
            }
        };

        loadTask.setOnSucceeded(e -> {
            Scene scene = new Scene(loadTask.getValue());
            Stage stage = new Stage();
            stage.initOwner(button.getScene().getWindow());
            stage.setScene(scene);
            stage.show();
        });

        loadTask.setOnFailed(e -> loadTask.getException().printStackTrace());

        Thread thread = new Thread(loadTask);
        thread.start();
    }
}

test.fxml:

TestController:

import javafx.fxml.FXML;
import javafx.scene.control.Label;

public class TestController {
    @FXML
    private Label label ;
    @FXML
    private void closeWindow() {
        label.getScene().getWindow().hide();
    }
}

Main application:

import java.io.IOException;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws IOException {
        primaryStage.setScene(new Scene(FXMLLoader.load(getClass().getResource("main.fxml"))));
        primaryStage.show();
    }

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

Notice that after pressing the button, you can still type in the text field during the five seconds it takes to "load" the FXML, so the UI is remaining responsive.