I am trying to drag and drop text from Google Chrome into a Java Swing application on Linux, but the drop event is not triggered in my Java application. However, the same drag-and-drop operation works fine in Firefox.

Observations:

• Dragging from Chrome to gedit works fine.
• Dragging from Chrome to a Java app on Windows works as expected.
• No exception is thrown in the Java application, and drop() is never called.

Environment:

$DISPLAY

Output: :0.11 (X11 is in use).

$XDG_SESSION_TYPE

Output: (No value returned).

I tried forcing X11 mode by running:

export XDG_SESSION_TYPE=x11

but the issue persists.

Minimal Java Swing drop handler code

import javax.swing.*;
import java.awt.*;
import java.awt.datatransfer.DataFlavor;
import java.awt.dnd.*;

public class DragDropSwingApp {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame("Drag & Drop Demo");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setSize(400, 300);

            JTextArea textArea = new JTextArea("Drop text here...");
            textArea.setFont(new Font("Arial", Font.PLAIN, 16));
            textArea.setLineWrap(true);
            textArea.setWrapStyleWord(true);
            textArea.setDropTarget(new DropTarget() {
                @Override
                public void drop(DropTargetDropEvent dtde) {
                    try {
                        dtde.acceptDrop(DnDConstants.ACTION_COPY);
                        Object data = dtde.getTransferable().getTransferData(DataFlavor.stringFlavor);
                        textArea.setText(data.toString());
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });

            frame.add(new JScrollPane(textArea), BorderLayout.CENTER);
            frame.setVisible(true);
        });
    }
}

Things I have checked:

• Java drop method never called:
  • drop() is not triggered when dragging from Chrome, but it works with Firefox.
• Clipboard handling & X11/Wayland differences:
  • Dragging works in other applications like gedit.
  • Installed xclip clipboard on Red Hat 8, but the issue persists.
• JCEF integration & Chromium conflicts:
  • I have Chromium installed separately for JCEF, but this shouldn't affect Java Swing drag-and-drop behavior.

Question:

Why does drag-and-drop from Chrome to Java Swing fail while it works with Firefox?
I guess this might be related to TransferHandler.canImport() not being called from Chromium in Ubuntu (JDK-8299842) in some way.
Are there any workarounds or Java settings to fix this issue?

I am trying to drag and drop text from Google Chrome into a Java Swing application on Linux, but the drop event is not triggered in my Java application. However, the same drag-and-drop operation works fine in Firefox.

Observations:

• Dragging from Chrome to gedit works fine.
• Dragging from Chrome to a Java app on Windows works as expected.
• No exception is thrown in the Java application, and drop() is never called.

Environment:

$DISPLAY

Output: :0.11 (X11 is in use).

$XDG_SESSION_TYPE

Output: (No value returned).

I tried forcing X11 mode by running:

export XDG_SESSION_TYPE=x11

but the issue persists.

Minimal Java Swing drop handler code

import javax.swing.*;
import java.awt.*;
import java.awt.datatransfer.DataFlavor;
import java.awt.dnd.*;

public class DragDropSwingApp {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame("Drag & Drop Demo");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setSize(400, 300);

            JTextArea textArea = new JTextArea("Drop text here...");
            textArea.setFont(new Font("Arial", Font.PLAIN, 16));
            textArea.setLineWrap(true);
            textArea.setWrapStyleWord(true);
            textArea.setDropTarget(new DropTarget() {
                @Override
                public void drop(DropTargetDropEvent dtde) {
                    try {
                        dtde.acceptDrop(DnDConstants.ACTION_COPY);
                        Object data = dtde.getTransferable().getTransferData(DataFlavor.stringFlavor);
                        textArea.setText(data.toString());
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });

            frame.add(new JScrollPane(textArea), BorderLayout.CENTER);
            frame.setVisible(true);
        });
    }
}

Things I have checked:

• Java drop method never called:
  • drop() is not triggered when dragging from Chrome, but it works with Firefox.
• Clipboard handling & X11/Wayland differences:
  • Dragging works in other applications like gedit.
  • Installed xclip clipboard on Red Hat 8, but the issue persists.
• JCEF integration & Chromium conflicts:
  • I have Chromium installed separately for JCEF, but this shouldn't affect Java Swing drag-and-drop behavior.

Question:

Why does drag-and-drop from Chrome to Java Swing fail while it works with Firefox?
I guess this might be related to TransferHandler.canImport() not being called from Chromium in Ubuntu (JDK-8299842) in some way.
Are there any workarounds or Java settings to fix this issue?

• java
• linux
• google-chrome
• drag-and-drop
• chromium

1 Answer 1

It is unusual to subclass DropTarget. I don’t know if that can be expected to work. In particular, you did not set a component on the DropTarget instance. The usual way to use the DropTarget class is to instantiate it:

textArea.setDropTarget(
    new DropTarget(textArea, DnDConstants.ACTION_COPY,
        new DropTargetAdapter() {
            @Override
            public void drop(DropTargetDropEvent) {
                // ...
            }
        }));

I’m not sure if this the cause of your issue, but… DataFlavor.stringFlavor does not correspond to the text/plain MIME type:

mimeType = "application/x-java-serialized-object"

The best way to receive text is with selectBestTextFlavor and getReaderForText:

@Override
public void drop(DropTargetDropEvent dtde) {
    try {
        dtde.acceptDrop(DnDConstants.ACTION_COPY);

        DataFlavor textFlavor =
            DataFlavor.selectBestTextFlavor(dtde.getCurrentDataFlavors());
        if (textFlavor != null) {
            StringWriter data = new StringWriter();
            try (Reader dataReader =
                textFlavor.getReaderForText(dtde.getTransferable())) {

                dataReader.transferTo(data);
            }
            textArea.setText(data.toString());
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

You also might be able to make it work using getTextPlainUnicodeFlavor(), which does correspond to text/plain, but it returns the data as a raw InputStream, which means you would have to obtain the native charset (which usually is not the same as Charset.defaultCharset()!), then convert the InputStream to a Reader in order to get the correct text. It’s easier to use the above approach.