Memory Leak with Swing Drag and Drop
- by tom
I have a JFrame that accepts top-level drops of files. However after a drop has occurred, references to the frame are held indefinitely inside some Swing internal classes. I believe that disposing of the frame should release all of its resources, so what am I doing wrong?
Example
import java.awt.datatransfer.DataFlavor;
import java.io.File;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.TransferHandler;
public class DnDLeakTester extends JFrame {
public static void main(String[] args) {
new DnDLeakTester();
//Prevent main from returning or the jvm will exit
while (true) {
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
}
}
}
public DnDLeakTester() {
super("I'm leaky");
add(new JLabel("Drop stuff here"));
setTransferHandler(new TransferHandler() {
@Override
public boolean canImport(final TransferSupport support) {
return (support.isDrop() && support
.isDataFlavorSupported(DataFlavor.javaFileListFlavor));
}
@Override
public boolean importData(final TransferSupport support) {
if (!canImport(support)) {
return false;
}
try {
final List<File> files = (List<File>)
support.getTransferable().getTransferData(DataFlavor.javaFileListFlavor);
for (final File f : files) {
System.out.println(f.getName());
}
} catch (Exception e) {
e.printStackTrace();
}
return true;
}
});
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
pack();
setVisible(true);
}
}
To reproduce, run the code and drop some files on the frame. Close the frame so it's disposed of.
To verify the leak I take a heap dump using JConsole and analyse it with the Eclipse Memory Analysis tool. It shows that sun.awt.AppContext is holding a reference to the frame through its hashmap. It looks like TransferSupport is at fault.
What am I doing wrong? Should I be asking the DnD support code to clean itself up somehow?
I'm running JDK 1.6 update 19.
