<AWT Dev>  Review Request for JDK-8024061: Exception thrown when drag and drop between two components is executed quickly
alexey.ivanov at oracle.com
Thu Apr 10 13:39:32 UTC 2014
If the requested data flavor is DataFlavor.javaJVMLocalObjectMimeType,
then transferable is local to the JVM. It is stored to a static variable
in SunDropTargetContextPeer.setCurrentJVMLocalSourceTransferable(). When
processEnterMessage() is handled, its value is copied to instance
variable "local". The instance variable is cleaned by
processExitMessage(), the static variable is cleared by
If drag-and-drop operation is performed quickly,
SunDragSourceContextPeer.cleanup() is called when mouse button is
released and *before* processEnterMessage() is called. So when EDT
finally handles MOUSE_ENTERED event and DropTargetListener.dragEnter()
gets called, "local" transferable is already null. The listener tries to
get the data from the transferable:
DropTargetDragEvent.getTransferable(), and then
The dataFlavor has MIME type of DataFlavor.javaJVMLocalObjectMimeType,
and SunDropTargetContextPeer.currentJVMLocalSourceTransferable is
already cleared. The representationClass field of the DataFlavor object
is set to java.io.InputStream.class. So when
SunDropTargetContextPeer.getNativeData() executes it tries to cast the
data object to java.io.InputStream to deserialize the data but fails
with the exception:
java.lang.ClassCastException: DnD$DropObject cannot be cast to
This exception is caught internally, and IOException is thrown as it
failed to get the data. At the same time, no IO should have occurred
because a local source was dragged, so this exception is rather unexpected.
What actually happens is that native drag-and-drop operation completed
already whereas this drag-and-drop operation on EDT didn't even started
yet. Does throwing InvalidDnDOperationException look more appropriate
than returning null in this case?
Sure, I'll submit a new bug for 9 to implement the proper fix.
On 10.04.2014 12:52, Petr Pchelko wrote:
> Hello, Dmitry.
> Thank you for the detailed explanation of the issue.
> I’m OK with this workaround as this should be back ported to 8u and 7u, but I think we could try to provide a real fix in 9.
> Could you please add some comment which shortly explains why the if clause was added?
> And could you also file a new bug for 9 so that we try to replace the workaround with a real fix?
> Thank you.
> With best regards. Petr.
> 10 апр. 2014 г., в 12:18 после полудня, Alexey Ivanov <alexey.ivanov at oracle.com> написал(а):
>> Hello AWT team,
>> Could you please review the fix for jdk9:
>> bug: https://bugs.openjdk.java.net/browse/JDK-8024061
>> webrev: http://cr.openjdk.java.net/~dmarkov/8024061/jdk9/webrev.00/
>> Problem description:
>> Dragging and dropping an object from one panel to another very quickly causes an exception.
>> The fix addresses only the thrown exception.
>> The dragged object would not be moved.
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