VenderController.java

@GetMapping(value = "/")
public String interfazVender(Model model, HttpServletRequest request) {
    model.addAttribute("producto", new Producto());
    float total = 0;
    ArrayList<ProductoParaVender> carrito = this.obtenerCarrito(request);
    for (ProductoParaVender p: carrito) total += p.getTotal();
    model.addAttribute("total", total);
    return "vender/vender";
}