Calling a Java method from a JavaFX webview

Question

In my project I have an HTML document that is displayed in a JavaFx WebView. I have a Javascript function that should call the Java method getData (currently it only prints the passed variable so that I can confirm the data is being passed from the WebView back to the Java application):

    public void getData(String s){
        System.out.println(s);
    }

This is how I am attempting to add the functionality to call Java methods into my WebView webpage:

    JSObject win = (JSObject) webEngine.getDocument();
    win.setMember("app", new Bridge());

And here is the JavaScript function that I'm using to call getData:

     function interOp(val){
        app.getData(val);
     }

This function is called on the onchange event on a <select> tag. The guides I have followed seem to do exactly this, however when I run my program nothing is printed on the console.

Answer 1

I have found a resolution for this issue: instead of using webEngine.getDocument();, which returns an HTMLdocument object, use webEngine.executeScript("window"); which gives a window object.

Answer 2

My solution was to create the object before passing it... so this:

JSObject win = (JSObject) webEngine.getDocument();
win.setMember("app", new Bridge());"

becomes this:

Bridge bridgeREF = new Bridge();
JSObject win = (JSObject) webEngine.getDocument();
win.setMember("app", bridgeREF);

This came from a bug report I read here: https://bugs.openjdk.java.net/browse/JDK-8170515

Otherwise, the javascript call seemed to work half the time... needed a refresh sometimes. It was really odd.

Though my code is/was a little different... here's how I register the java class "JavaApp" with the JavaFX window:

        Platform.runLater(new Runnable() {
        @Override
        public void run() {

  JavaApp appREF = new JavaApp(webEngine); 
  webEngine.getLoadWorker().stateProperty().addListener(
        new ChangeListener<State>() {
          @Override public void changed(ObservableValue ov, State oldState, State newState) {

              if (newState == Worker.State.SUCCEEDED) {

                  JSObject win = (JSObject) webEngine.executeScript("window");
                    win.setMember("app", appREF);  
            }

            }
        });
   //other code for loading html, listeners, etc...
   }

The reference to the class should be created outside of the anonymous listener, else the garbage collector might get it. Which is what (I think) was causing the erratic behavior I was experiencing... your java class may or may not need the reference to webEngine.. I use that for loading another url after sending a file.

I don't think it matters whether you use Window or Document... except that window might be more persistent depending on whether you use full page loads or not.