尝试使用Media Player时Application Constructor中的异常

Question

I have written a code which will play music when a link on a webpage is found.

import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Application;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;
import javafx.application.*;
// * @author Archit

public abstract class WebCrawl extends Application{

    public static void main(String[] args) throws IOException {
        Application.launch(args);
        int a=0;
        try {
            Document doc = Jsoup.connect("https://in.bookmyshow.com/ranchi").get();
            org.jsoup.select.Elements links = doc.select("a");
            for (Element e: links) {
                if ((e.attr("abs:href").equals("https://in.bookmyshow.com/ranchi/movies/fan/ET00025074"))) {
                    try {
                        File f = new File("/Users/Archit/Documents/Music/campbell.wav");
                        Media hit = new Media(f.toURI().toString());
                        MediaPlayer mediaPlayer = new MediaPlayer(hit);
                        mediaPlayer.play();
                    } catch(Exception ex) {
                        System.out.println("Exception");
                    }
                }
            }
        }

The error I am getting is this:

Exception in Application constructor java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at       sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Unable to construct Application   instance: class webcrawl.WebCrawl
    at   com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:907)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.InstantiationException
    at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:819)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
Exception running application webcrawl.WebCrawl

A window seems to open when I run the application but is automatically closed and this error appears.

I would really appreciate the help. Thank you.

Answer 1

You are starting an application from the WebCrawl class using Application.launch(String[]) , so launch tries to create a WebCrawl instance, which it can't, since WebCrawl is abstract .

BTW: Placing code after the Application.launch call won't work, since after Application.launch is finished, the JavaFX platform will already have exited.

You can read about the application lifecycle in the Life-cycle section of the Application javadoc .

You need to call the code form the start method or later.

You can find a tutorial for a simple JavaFX application here: https://docs.oracle.com/javase/8/javafx/get-started-tutorial/hello_world.htm