如何在java中多次调用launch()

Question

如何在 java 中多次调用 launch() 我得到一个异常为“ERROR IN MAIN:java.lang.IllegalStateException: Application launch must not be called more than once”

当请求到来时，我在我的 java 应用程序中创建了 rest cleint，它调用 javafx 并在完成 webview 操作后打开 webview，我正在使用 Platform.exit() 方法关闭 javafx 窗口。当第二个请求到来时，我收到此错误如何解决此错误。

JavaFx 应用程序代码：

public class AppWebview extends Application  {

    public static Stage stage;

    @Override
    public void start(Stage _stage) throws Exception {

        stage = _stage;
        StackPane root = new StackPane();

        WebView view = new WebView();

        WebEngine engine = view.getEngine();
        engine.load(PaymentServerRestAPI.BROWSER_URL);
        root.getChildren().add(view);
        engine.setJavaScriptEnabled(true);
        Scene scene = new Scene(root, 800, 600);
        stage.setScene(scene);

        engine.setOnResized(new EventHandler<WebEvent<Rectangle2D>>() {
            public void handle(WebEvent<Rectangle2D> ev) {
                Rectangle2D r = ev.getData();
                stage.setWidth(r.getWidth());
                stage.setHeight(r.getHeight());
            }
        });

        JSObject window = (JSObject) engine.executeScript("window");
        window.setMember("app", new BrowserApp());

        stage.show();

    }

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

RestClient 方法： 调用 JavaFX 应用程序

// method 1 to lanch javafx
javafx.application.Application.launch(AppWebview.class);

// method 2 to lanch javafx
String[] arguments = new String[] {"123"};
AppWebview .main(arguments);

Answer 1

您不能在 JavaFX 应用程序上多次调用 launch()，这是不允许的。

来自 javadoc：

It must not be called more than once or an exception will be thrown.

定期显示窗口的建议

1. 只需拨打一次Application.launch()。
2. 使用 Platform.setImplicitExit(false) 保持 JavaFX 运行时在后台运行，这样当您隐藏最后一个应用程序窗口时 JavaFX 不会自动关闭。
3. 下次您需要另一个窗口时，将窗口show() 调用包装在Platform.runLater() 中，以便在JavaFX 应用程序线程上执行调用。

对于此方法的简短摘要实现：

• 见answer by sergioFC

如果您正在混合 Swing，您可以使用 JFXPanel 而不是 Application，但使用模式将与上面概述的相似。

• 有关 JFXPanel 方法的示例，请参阅 Irshad Babar s answer。

Wumpus 样本

这个例子比它需要的要复杂一些，因为它还涉及定时器任务。但是，它确实提供了一个完整的独立示例，有时可能会有所帮助。

import javafx.animation.PauseTransition;
import javafx.application.*;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.stage.Stage;
import javafx.util.Duration;

import java.util.*;

// hunt the Wumpus....
public class Wumpus extends Application {
    private static final Insets SAFETY_ZONE = new Insets(10);
    private Label cowerInFear = new Label();
    private Stage mainStage;

    @Override
    public void start(final Stage stage) {
        // wumpus rulez
        mainStage = stage;
        mainStage.setAlwaysOnTop(true);

        // the wumpus doesn't leave when the last stage is hidden.
        Platform.setImplicitExit(false);

        // the savage Wumpus will attack
        // in the background when we least expect
        // (at regular intervals ;-).
        Timer timer = new Timer();
        timer.schedule(new WumpusAttack(), 0, 5_000);

        // every time we cower in fear
        // from the last savage attack
        // the wumpus will hide two seconds later.
        cowerInFear.setPadding(SAFETY_ZONE);
        cowerInFear.textProperty().addListener((observable, oldValue, newValue) -> {
            PauseTransition pause = new PauseTransition(
                    Duration.seconds(2)
            );
            pause.setOnFinished(event -> stage.hide());
            pause.play();
        });

        // when we just can't take it  anymore,
        // a simple click will quiet the Wumpus,
        // but you have to be quick...
        cowerInFear.setOnMouseClicked(event -> {
            timer.cancel();
            Platform.exit();
        });

        stage.setScene(new Scene(cowerInFear));
    }

    // it's so scary...
    public class WumpusAttack extends TimerTask {
        private String[] attacks = {
                "hugs you",
                "reads you a bedtime story",
                "sings you a lullaby",
                "puts you to sleep"
        };

        // the restaurant at the end of the universe.
        private Random random = new Random(42);

        @Override
        public void run() {
            // use runlater when we mess with the scene graph,
            // so we don't cross the streams, as that would be bad.
            Platform.runLater(() -> {
                cowerInFear.setText("The Wumpus " + nextAttack() + "!");
                mainStage.sizeToScene();
                mainStage.show();
            });
        }

        private String nextAttack() {
            return attacks[random.nextInt(attacks.length)];
        }
    }

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

2020 年 1 月更新

Java 9 添加了一个名为Platform.startup() 的新功能，您可以使用它来触发JavaFX 运行时的启动，而无需定义派生自Application 的类并在其上调用launch()。 Platform.startup() 与 launch() 方法有类似的限制（您不能多次调用 Platform.startup()），因此如何应用它的元素类似于此答案中的 launch() 讨论和 Wumpus 示例。

有关如何使用 Platform.startup() 的演示，请参阅 Fabian 对 How to achieve JavaFX and non-JavaFX interaction? 的回答

Answer 2

我使用类似的东西，类似于其他答案。

private static volatile boolean javaFxLaunched = false;

public static void myLaunch(Class<? extends Application> applicationClass) {
    if (!javaFxLaunched) { // First time
        Platform.setImplicitExit(false);
        new Thread(()->Application.launch(applicationClass)).start();
        javaFxLaunched = true;
    } else { // Next times
        Platform.runLater(()->{
            try {
                Application application = applicationClass.newInstance();
                Stage primaryStage = new Stage();
                application.start(primaryStage);
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
    }
}

Answer 3

试试这个，我试过这个，发现成功了

@Override
public void start() {
    super.start();
    try {
                    // Because we need to init the JavaFX toolkit - which usually Application.launch does
                    // I'm not sure if this way of launching has any effect on anything
        new JFXPanel();

        Platform.runLater(new Runnable() {
            @Override
            public void run() {
                // Your class that extends Application
                new ArtisanArmourerInterface().start(new Stage());
            }
        });
    } catch (Exception e) {
        e.printStackTrace();
    }
}