OrderControllerV2.java

//...

private final PaymentService paymentService;

public OrderController(PaymentService paymentService) {
    this.paymentService = paymentService;
}

@PostMapping
public String placeOrder(@RequestParam Double totalAmount, HttpServletRequest request){
    final URI returnUrl = buildReturnUrl(request);
    CreatedOrder createdOrder = paymentService.createOrder(totalAmount, returnUrl);
    return "";
}

//...