Order controller and DTOs

When a request comes to the server to order a bunch of products, it comes in an HTTPS POST request. The body of the request is encoded in JSON. Till now, we had controllers that were handling GET parameters. Handling POST requests are not much more difficult when we can rely on the data marshaling of Spring. The controller code itself is simple:

package packt.java11.bulkorder.controllers;

import ...

@RestController
public class OrderController {
    private static final Logger log = LoggerFactory.getLogger((OrderController.class));
    private final Checker checker;

    public OrderController(@Autowired Checker checker) {
        this.checker = checker;
    }

    @RequestMapping("/order")
    public Confirmation getProductInformation(@RequestBody Order order) {
        if (checker.isConsistent(order)) {
            return Confirmation.accepted...