Spring boot Can'；t从改装回调返回CompletableFuture.completedFuture

弹簧靴2.2 改装2

我需要创建异步http请求。返回结果后重定向到

重定向：/cart

她是我的控制器：

 @Autowired
    private OrderService orderService;

    @PostMapping(value = "/productEntry")
    public String submitProductEntry(ProductEntry productEntry, Model model) {
        try {
            orderService.addProductToCart(productEntry);
        } catch (InterruptedException e) {
            logger.error(e);
        }
        return "redirect:/cart";
    }

这是我的服务：

@Service
public class OrderService {

    private static Logger logger = LogManager.getLogger(OrderService.class);

    @Async
    public CompletableFuture<Cart> addProductToCart(ProductEntry productEntry) throws InterruptedException {
        logger.info("addProductToCart: productEntry = " + productEntry);
        TransportService.addProductToCart(productEntry, new DefaultRestClientCallback<JsonElement>() {
            @Override
            public void onSuccess(Response<JsonElement> response) {
                //super.onSuccess(response);
                JsonElement responseJson = response.body();
                logger.info("addProductToCart: onSuccess: responseJson = " + responseJson);
                Cart cart = GsonUtil.gson.fromJson(responseJson, Cart.class);
                logger.info("addProductToCart: cart = " + cart);
                return CompletableFuture.completedFuture(cart);
            }

            @Override
            public void onError(ErrorResponse errorResponse) {
                //super.onError(errorResponse);
                logger.error("addProductToCart: error = " + errorResponse);
            }
        });

    }

}

错误：

Cannot return a value from a method with void result type

return CompletableFuture.completedFuture(cart);

Cannot return a value from a method with void result type