Drag and Drop not working on Linux when running via jPro LoadBalancer

[KniKnaKnorke]

Hello,

I have the following sample code that implements a simple drag-and-drop feature. Items in the list can be moved to different positions.

public class Launcher extends JProApplication {

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

    @Override
    public void start(Stage stage) throws Exception {
        ObservableList<String> items = FXCollections.observableArrayList(
                "Item 1", "Item 2", "Item 3", "Item 4", "Item 5"
        );

        ListView<String> listView = new ListView<>(items);

        // Custom cells for drag & drop reorder
        listView.setCellFactory(lv -> {
            ListCell<String> cell = new ListCell<>() {
                @Override
                protected void updateItem(String item, boolean empty) {
                    super.updateItem(item, empty);
                    setText(empty ? null : item);
                }
            };

            // Start dragging
            cell.setOnDragDetected(e -> {
                System.err.println("setOnDragDetected");
                if (cell.isEmpty()) return;

                Dragboard db = cell.startDragAndDrop(TransferMode.MOVE);
                ClipboardContent content = new ClipboardContent();
                content.putString(cell.getItem()); // store item text
                db.setContent(content);

                // remember source index
                listView.getProperties().put("dragSourceIndex", cell.getIndex());
                e.consume();
            });

            // While dragging over a cell
            cell.setOnDragOver(e -> {
                System.err.println("setOnDragOver");
                if (cell.isEmpty()) return;

                Integer sourceIndex = (Integer) listView.getProperties().get("dragSourceIndex");
                if (sourceIndex == null) return;

                if (e.getGestureSource() != cell && e.getDragboard().hasString()) {
                    e.acceptTransferModes(TransferMode.MOVE);
                }
                e.consume();
            });

            // Drop onto a cell => reorder
            cell.setOnDragDropped(e -> {
                System.err.println("setOnDragDropped");
                Dragboard db = e.getDragboard();
                boolean success = false;

                Integer sourceIndex = (Integer) listView.getProperties().get("dragSourceIndex");
                if (sourceIndex != null && db.hasString() && !cell.isEmpty()) {
                    int targetIndex = cell.getIndex();

                    if (sourceIndex != targetIndex) {
                        String moved = items.remove((int) sourceIndex);

                        // if you remove an item above the target, the target index shifts by -1
                        if (sourceIndex < targetIndex) targetIndex--;

                        items.add(targetIndex, moved);
                        listView.getSelectionModel().select(targetIndex);
                    }
                    success = true;
                }

                e.setDropCompleted(success);
                e.consume();
            });

            // Cleanup
            cell.setOnDragDone(e -> {
                listView.getProperties().remove("dragSourceIndex");
                e.consume();
            });

            return cell;
        });

        stage.setTitle("JavaFX ListView Drag & Drop");
        stage.setScene(new Scene(listView, 300, 220));
        stage.show();
    }
}

When I run this code on Linux using Gradle or from the release package, drag and drop works perfectly.

However, when I run the application through the jPro LoadBalancer, drag and drop no longer works. It seems that the dragDetected event is still triggered, but no further drag-and-drop events occur.

I also noticed that on Windows, drag and drop works fine even when using the LoadBalancer.

System Information:
OS: Linux
jPro / LoadBalancer: 2026.1.0
Java / JavaFX: 21

Greetings,
Dennis Nolte

[FlorianKirmaier]

Hm, interesting.
We will investigate is.
Quite suspiciouse that you mention it depends on the Loadbalancer.
Are you sure about it? These are basically just mouse-events interpreted as D&D - there isn't really a place, where the Loadbalancer can interfere much. Maybe It's another Variable? Like always failing on Linux?

[KniKnaKnorke]

I just found the solution.

The problem was that the release package was built on Windows using the platform flag for Linux in gradle. When I ran this package on Linux with the LoadBalancer, drag and drop did not work.

However, when I created the release package directly on Linux and then ran it with the LoadBalancer, drag and drop worked correctly.

So it seems there may be an issue with files generated on Windows (possibly related to line endings or file formatting), causing something not to be parsed properly on Linux.

[FlorianKirmaier]

That sounds reasonable.
You konw have 2 release zips, where one works?
Any noticeable difference? Maybe a different JavaFX Version?

[KniKnaKnorke]

The JavaFX version is always the same, and I am using the same branch in all cases.

Windows Release Package
I can create a release package on Windows using the Linux platform flag and use this package in my Docker image to run the application with the LoadBalancer. In this setup, the application itself works correctly on Linux.
However, drag and drop does not work in this case.

Linux Release Package
The scenario where everything works as expected is when I create the release package on Linux and then run it in Docker with the LoadBalancer.

[KniKnaKnorke]

Here is the vmoptions file

vmoptions.txt

[FlorianKirmaier]

Can you test it with 2026.1.1-RC1?
It should no no longer create OS-Dependent vmoptions.txt files.

[KniKnaKnorke]

Unfortunately, it still doesn’t work on Linux when I create the package on Windows. The vmoptions file has still CRLF linebreaks

[FlorianKirmaier]

Can you try 2026.1.1-RC2 in 10 minutes?

[KniKnaKnorke]

With this version, it works when it is released on Windows and executed on Linux