ADDITIONAL SYSTEM INFORMATION :
Linux; KDE Plasma Version 6.1.3, Wayland

A DESCRIPTION OF THE PROBLEM :
When you run attached code and try to drag and drop a file whose filename contains '[', URISyntaxException exception is thrown. This is due to the fact that KDE provides the filename with url-encoding which is invalid when constructing an URL class. An example of file path that causes the exception: /home/michal/].txt.

There are many other characters that causes the exception I mentioned. [ is one of them.

The solution to the problem seems to be very easy. Every filename should be url-decoded. JDK provides a utility method for that: java.net.URLDecoder.decode(String s, String enc).

This bug is present in JDK 21 and in openjdk 24-ea 2025-03-18.

I would be delighted if I could write fix for this bug.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the provided code and try to drag and drop a file whose filename contains [ character.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Drag and Drop of a file whose name contains the [ character does not cause an exception. An application is able to get a drag-and-dropped filename correctly.
ACTUAL -
java.awt.dnd.InvalidDnDOperationException: java.net.URISyntaxException: Illegal character in path at index 20: file:///home/michal/].txt
at java.desktop/sun.awt.dnd.SunDropTargetContextPeer.getTransferData(SunDropTargetContextPeer.java:274)
at java.desktop/sun.awt.datatransfer.TransferableProxy.getTransferData(TransferableProxy.java:73)
at java.desktop/java.awt.dnd.DropTargetContext$TransferableProxy.getTransferData(DropTargetContext.java:387)
at com.github.michal.SimpleDnD$1.drop(SimpleDnD.java:30)
at java.desktop/sun.awt.dnd.SunDropTargetContextPeer.processDropMessage(SunDropTargetContextPeer.java:548)
at java.desktop/sun.awt.X11.XDropTargetContextPeer.processDropMessage(XDropTargetContextPeer.java:185)
at java.desktop/sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchDropEvent(SunDropTargetContextPeer.java:864)
at java.desktop/sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchEvent(SunDropTargetContextPeer.java:788)
at java.desktop/sun.awt.dnd.SunDropTargetEvent.dispatch(SunDropTargetEvent.java:48)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2324)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2780)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4828)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:775)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:720)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:714)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:98)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:747)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:400)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:744)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

---------- BEGIN SOURCE ----------
import javax.swing.*;
import java.awt.datatransfer.DataFlavor;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetDropEvent;
import java.io.File;
import java.util.List;

public class SimpleDnD extends JFrame {

    public SimpleDnD() {

        setTitle("Drag & Drop Demo");

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        setSize(500, 500);

        setVisible(true);

        setDropTarget(new DropTarget() {
            @Override
            public void drop(DropTargetDropEvent evt) {
                try {
                    evt.acceptDrop(DnDConstants.ACTION_COPY);
                    List<File> droppedFiles = (List<File>)
                            evt.getTransferable().getTransferData(DataFlavor.javaFileListFlavor);
                    evt.dropComplete(true);
                } catch(Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(SimpleDnD::new);
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Change filename to avoid characters that causes problems.

FREQUENCY : always