错误时从URL加载图像和默认图像

Question

I am trying to load an image from a URL and this was very easy and works great. However, if the image doesnt exist I want it to default to a local image. The problem I am having is that it doesnt throw any exceptions. Instead it will just not display anything. I'm assuming I have to validate the URL some how, but I want to also be sure that its an image and not a webpage/script...etc

Here is my basic test code. This works:

public class DownloadImage extends Application {

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

    @Override
    public void start(Stage primaryStage) {

        VBox root = new VBox();

        String imageSource = "https://www.wbkidsgo.com/Portals/1/Content/Hero/HeroBugsCarrot/Source/Default/WB_LT_HeroImage_Bugs_v1.png";

        ImageView imageView = new ImageView(new Image(imageSource));

        root.getChildren().add(imageView);

        primaryStage.setScene(new Scene(root, 1000, 1000));
        primaryStage.show();

    }
}

But if I load a bad URL ie (two s's in Portals):

String imageSource = "https://www.wbkidsgo.com/Portalss/1/Content/Hero/HeroBugsCarrot/Source/Default/WB_LT_HeroImage_Bugs_v1.png";

It will just be blank. I thought about creating an HTTP client and sending a request prior to creating the image, but generating the HTTP client takes a few seconds and I will be loading upwards of 300 or so images. I guess I can have one http client, and make one request for each image and check the response datatype to see if its an image, but is there a better way?

Answer 1

You can use the errorProperty and exceptionProperty to check the error status of the image:

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.image.Image;
import javafx.stage.Stage;

public class ImageTest extends Application {

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

    @Override
    public void start(Stage primaryStage) {
        String[] urls = new String[]{
                "https://www.wbkidsgo.com/Portals/1/Content/Hero/HeroBugsCarrot/Source/Default/WB_LT_HeroImage_Bugs_v1.png",
                "https://www.wbkidsgo.com/Portalss/1/Content/Hero/HeroBugsCarrot/Source/Default/WB_LT_HeroImage_Bugs_v1.png"
        } ;

        for (String url : urls) {
            Image image = new Image(url);
            if (image.isError()) {
                System.out.println("Error loading image from "+url);
                // if you need more details
                // image.getException().printStackTrace();
            } else {
                System.out.println("Successfully loaded image from " + url);
            }
        }
        Platform.exit();
    }

}

Which gives the following output:

Successfully loaded image from https://www.wbkidsgo.com/Portals/1/Content/Hero/HeroBugsCarrot/Source/Default/WB_LT_HeroImage_Bugs_v1.png
Error loading image from https://www.wbkidsgo.com/Portalss/1/Content/Hero/HeroBugsCarrot/Source/Default/WB_LT_HeroImage_Bugs_v1.png

Answer 2

You can use the ImageView.setImage() method to change the image. I recommend initializing the ImageView using your default image in the form of a BufferedImage , then setting it later with your actual image. You can load this from your filesystem or classpath using ImageIO .

As for the actual image, I would also use ImageIO to load the url as a BufferedImage . This throws an IOException , so if it errors or does not link to a supported image type, nothing will happen.

If you know much about threads and concurrency, I would load the image on another thread so it doesn't freeze your main thread.