Calculate order average payment placed on 14-Mar-2021:Answ=287.604

AvgPayment.java

    @RequestMapping("/avg-payment")
    public Double getAvgPayment(@RequestParam("date") final Optional<String> date) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        return orderRepo.findAll().stream().filter(o -> o.getOrderDate().isEqual(LocalDate.
                        parse(date.get(), formatter))).flatMap(o -> o.getProducts().stream()).mapToDouble(p ->
                p.getPrice()).average().getAsDouble();
    }