GayanM

    @RequestMapping("/recent")
    public List<Order> getRecentOrders (@RequestParam("limit") final Optional<Long> limit) {
        return orderRepo.findAll().stream().
                sorted(Comparator.
                        comparing(com.mycompany.functional.programming.exercises.models.Order::getOrderDate).
                        reversed()).limit(limit.get()).map(o -> new Order(o.getId(), o.getOrderDate(),
                        o.getDeliveryDate(), o.getStatus())).collect(Collectors.toList());
    }

GayanM

    @RequestMapping("/cheapest")
    public Optional<Product> getCheapestProductByCategory(@RequestParam("category") final Optional<String> category) {
        return productRepos.findAll().stream().filter(p -> {
            if (category.isEmpty()) {
                return true;
            }
            return category.get().equalsIgnoreCase(p.getCategory());
        }).min(Comparator.comparing(com.mycompany.functional.programming.exercises.models.Product::getPrice)).map(p ->
                new Product(p.getId(), p.getName(), p.getPrice(), p.getCategory()));
    }

GayanM

    @RequestMapping("/customer-tier")
    public List<Product> getProductsByCustomerTier (@RequestParam("tier") final Optional<Integer> tier,
                                                    @RequestParam("start-date") final Optional<String> startDate,
                                                    @RequestParam("end-date") final Optional<String> endDate) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        return orderRepo.findAll().stream().
               filter(o -> {
                   if (tier.isEmpty()) {
                       return true;
                   }

GayanM

    @RequestMapping("/discount")
    public List<Product> applyDiscountOnCategory(@RequestParam("category") final Optional<String> category,
                                                 @RequestParam("discount") final Optional<Double> discount) {
        return productRepos.findAll().stream().
               filter(p -> {
                   if (category.isEmpty()) {
                       return true;
                   }
                   return category.get().equalsIgnoreCase(p.getCategory());
               }).map(p -> {

GayanM

    @RequestMapping("")
    public List<Order> getOrdersByProductCategory (@RequestParam("category") final Optional<String> category) {
        return orderRepo.findAll().stream().
                filter(o -> o.getProducts().stream().anyMatch(p -> {
                    if (category.isEmpty()) {
                        return true;
                    }
                    return category.get().equalsIgnoreCase(p.getCategory());
                })).
                map(o -> new Order(o.getId(), o.getOrderDate(), o.getDeliveryDate(), o.getStatus())).

GayanM

@RequestMapping("")
    public List<Product> filterProducts(@Param("category") final Optional<String> category,
                                        @Param("lower-price-limit") final Optional<Double> lowerLimitPrice,
                                        @RequestParam("upper-price-limit") final Optional<Double> upperLimitPrice ) {


        return productRepos.findAll().stream().
                filter(p -> {
                    if (category.isEmpty()) {
                        return true;