viewer.addDropSupport(DND.DROP_COPY , new Transfer[] { LocalSelectionTransfer.getTransfer() }, new ViewerDropAdapter(viewer) {

			@Override
			public boolean validateDrop(Object target, int operation, TransferData transferType) {
				overrideOperation(DND.DROP_COPY );
				return true;
			}

			@Override
			public boolean performDrop(Object data) {
				// TODO Auto-generated method stub
				return false;
			}
		});

DropTarget dt = new DropTarget(myLabel, DND.DROP_COPY);
Transfer[] types = new Transfer[] { ClientFileTransfer.getInstance(), TextTransfer.getInstance() };
dt.setTransfer(types);
dt.addDropListener(myDropTargetListener);

public DropTargetListener myDropTargetListener = new DropTargetListener() {
		@Override
		public void dragEnter(DropTargetEvent e) {
			e.detail = DND.DROP_COPY;
		}

		@Override
		public void dragLeave(DropTargetEvent e) {
			e.detail = DND.DROP_COPY;
		}

		@Override
		public void dragOperationChanged(DropTargetEvent e) {
			e.detail = DND.DROP_COPY;
		}

		@Override
		public void dragOver(DropTargetEvent e) {
			e.detail = DND.DROP_COPY;
		}

		@Override
		public void drop(DropTargetEvent e) {
			if (e.data.getClass().equals(ClientFileImpl[].class)) {
				ClientFile[] lst = (ClientFile[])e.data;
				if (lst != null && lst.length > 0) {
					for (int i = 0; i < lst.length; i++) {
						System.out.println("    ClientFile[" + i + "]=" + lst[i] + " class: " + lst[i].getClass() + " name: " + lst[i].getName();
					}
				}
			}
		}

		@Override
		public void dropAccept(DropTargetEvent e) {
			e.detail = DND.DROP_COPY;
		}
};

...
@Override
public void drop(DropTargetEvent e) {
	if (e.data.getClass().equals(ClientFileImpl[].class)) { // list of files
		ClientFile[] lst = (ClientFile[])e.data;
		if (lst != null && lst.length > 0) {
			ClientFileUploader uploader = RWT.getClient().getService(ClientFileUploader.class);
			receiver = new DiskFileUploadReceiver(); // globally defined in owning class
			FileUploadHandler handler = new FileUploadHandler(receiver);
			String url = handler.getUploadUrl();
			handler.addUploadListener(fuListener);
			uploader.submit(url, lst);
		}
	}
}
...

public FileUploadListener fuListener = new FileUploadListener() {
	@Override
	public void uploadProgress(FileUploadEvent e) {
		System.out.println("fuListener.uploadProgress: " + e);
	}

	@Override
	public void uploadFinished(FileUploadEvent e) {
		System.out.println("fuListener.uploadFinished: " + e);
		File[] files = receiver.getTargetFiles();
		if (files != null && files.length > 0) {
			for (int f = 0; f < files.length; f++) {
				System.out.println("file[" + f + "]=" + files[f]);
			}
		}
	}

	@Override
	public void uploadFailed(FileUploadEvent e) {
		System.out.println("fuListener.uploadFailed: " + e);
	}
};