gistfile1.java

        view.getTree().addOpenHandler(new OpenHandler<TreeItem>() {
            @Override public void onOpen(final OpenEvent<TreeItem> event) {
                if (needsLoading(event.getTarget())) {
                    vfsService.call(new RemoteCallback<DirectoryStream<Path>>() {
                        @Override
                        public void callback(DirectoryStream<Path> response) {
                            event.getTarget().getChild(0).remove();
                            for (final Path path : response) {
                                vfsService.call(new RemoteCallback<Map>() {
                                    @Override
                                    public void callback(final Map response) {
                                        final BasicFileAttributes attrs = VFSTempUtil.toBasicFileAttributes(response);
                                        final TreeItem item;
                                        if (attrs.isDirectory()) {
                                            item = event.getTarget().addItem(Util.getHeader(images.openedFolder(), path.getFileName()));
                                            item.addItem(LAZY_LOAD);
                                        } else {
                                            item = event.getTarget().addItem(Util.getHeader(images.file(), path.getFileName()));
                                        }
                                        item.setUserObject(path);
                                    }
                                }).readAttributes(path);
                            }
                        }
                    }).newDirectoryStream((Path) event.getTarget().getUserObject());
                }
            }
        });