据我了解,调用Platform.exit()只是发出JavaFX Toolkit关闭的信号,导致在FX Application线程上调用应用程序实例的stop()方法,并允许FX应用程序线程终止.这反过来导致Application.launch()返回.如果你在main(…)方法中使用通常的习语：

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

然后一旦launch()返回,main()方法就没有任何东西可以做了,并且没有(只要没有运行非守护程序线程)应用程序以正常方式退出.在任何情况下,Platform.exit()都不会创建对System.exit(…)的调用：但是在某些情况下,它将允许JVM退出,因为它没有任何东西可以执行.

如果你调用System.exit(…),JVM基本上会立即退出.因此,例如,如果在Application.launch()之后的main(…)方法中有代码,那么在调用Platform.exit()之后执行该代码,而不是在调用System.exit之后执行(. ..).类似地,如果重写Application.stop(),则在调用Platform.exit()之后调用stop()方法,但在调用System.exit(…)之后不调用.

如果您运行非守护程序线程,Platform.exit()将不会强制关闭它们,但System.exit()将会.

以下示例应演示此：

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class ExitTest extends Application {

    @Override
    public void stop() {
        System.out.println("Stop called");
    }

    @Override
    public void start(Stage primaryStage) {
        Button startThread = new Button("Start non-daemon thread");
        startThread.setOnAction(e -> new Thread(() -> {
            System.out.println("Starting thread");
            try {
                Object lock = new Object();
                synchronized(lock) {
                    lock.wait();
                }
            } catch (InterruptedException exc) {
                System.err.println("Interrupted");
                Thread.currentThread().interrupt();
            } finally {
                System.out.println("Thread complete");
            }
        }).start());

        Button exit = new Button("Simple Exit");
        exit.setOnAction(e -> {
            System.out.println("Calling Platform.exit()");
            Platform.exit();
        });

        Button forceExit = new Button("Force exit");
        forceExit.setOnAction(e -> {
            System.out.println("Calling Platform.exit():");
            Platform.exit();
            System.out.println("Calling System.exit(0):");
            System.exit(0);
        });

        Scene scene = new Scene(new HBox(5,startThread,exit,forceExit));
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
        System.out.println("launch() complete");
    }
}

通常建议您通过调用Platform.exit()来退出JavaFX应用程序,这样可以正常关闭：例如,如果您需要任何“清理”代码,可以将它放在stop()方法中,Platform.exit()将允许它被执行.如果您正在运行必须终止的后台线程,请使它们成为守护程序线程,或者通过执行程序服务执行它们,并从stop()方法关闭执行程序服务.以下是使用该技术的上述示例的修改.

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class ExitTest extends Application {

    private final ExecutorService exec = Executors.newCachedThreadPool();

    @Override
    public void stop() throws InterruptedException {
        System.out.println("Stop called: try to let background threads complete...");
        exec.shutdown();
        if (exec.awaitTermination(2,TimeUnit.SECONDS)) {
            System.out.println("Background threads exited");
        } else {
            System.out.println("Background threads did not exit,trying to force termination (via interruption)");
            exec.shutdownNow();
        }       
    }

    @Override
    public void start(Stage primaryStage) {
        Button startThread = new Button("Start non-daemon thread");
        startThread.setOnAction(e -> { 
            exec.submit( () -> {
                System.out.println("Starting thread");
                try {
                    // just block indefinitely:
                    Object lock = new Object();
                    synchronized(lock) {
                        lock.wait();
                    }
                } catch (InterruptedException exc) {
                    System.out.println("Interrupted");
                    Thread.currentThread().interrupt();
                } finally {
                    System.out.println("Thread complete");
                }
            });
        });

        Button exit = new Button("Simple Exit");
        exit.setOnAction(e -> {
            System.out.println("Calling Platform.exit()");
            Platform.exit();
        });


        Scene scene = new Scene(new HBox(5,exit));
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
        System.out.println("launch() complete");
    }
}

如果要使用Platform.exit()以便正常关闭,并且希望从System.exit(…)返回值,则以下方法应该有效.请注意,这实际上并不是一种推荐的做法：在生产代码中,您根本不应该依赖支持流程退出代码的平台.

public class App extends Application {

    private static int exitCode = 0 ;

    public static exit(int exitCode) {
        App.exitCode = exitCode ;
        Platform.exit();
    }

    @Override
    public void start(Stage primaryStage) {
        // ...

        someThing.addEventHander(someEventType,e -> App.exit(42));

        // ...
    }

    @Override
    public void stop() {
        // cleanup code...
    }

    public static void main(String[] args) {
        Application.launch(args);
        System.exit(exitCode);
    }
}