I am trying to create an application in Spring Boot. I am defining the methods updateBasket and removeItem but they seem to be having issues. When I ran the project, and in the form when I click let’s say “Update Quantity” it threw me a Whitelabel error, saying Bad request type, status 400. Tomcat server logs shows:

“Resolved [org.springframework.web.bind.MissingServletRequestParameterException: Required request parameter ‘itemId’ for method parameter type Long is present but converted to null]”

package com.example.test1.controller;

import com.example.test1.model.Beverage;
import com.example.test1.model.OrderItem;
import com.example.test1.model.Order;
import com.example.test1.service.BeverageService;
import com.example.test1.service.OrderItemService;
import com.example.test1.service.OrderService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import jakarta.servlet.http.HttpServletRequest;
// Import the HttpServletRequest

import java.text.DecimalFormat;

import jakarta.servlet.http.HttpSession;
import java.util.List;
import java.util.ArrayList;

@Controller
public class BasketController {

    @Autowired
    private BeverageService beverageService;

    @Autowired
    private OrderItemService orderItemService;

    @Autowired
    private OrderService orderService;

    @GetMapping("/basket")
    public String showBasket(HttpSession session, Model model) {
        // Retrieve the basket from the session
        List<OrderItem> basket = (List<OrderItem>) session.getAttribute("basket");

        // If the basket is null (i.e., no items in the basket), initialize it
        if (basket == null) {
            basket = new ArrayList<>();
        }

        // Calculate the total price
        double totalPrice = 0;
        for (OrderItem item : basket) {
            totalPrice += item.getPrice();
        }

        // Add the basket and the total price to the model so it can be accessed in the Thymeleaf template
        model.addAttribute("items", basket);
        model.addAttribute("totalPrice", totalPrice);

        // Return the name of the Thymeleaf template to render
        return "basket";  // This refers to the "basket.html" template
    }

    // Add beverage to basket
    // BasketController.java
    @PostMapping("/add-to-basket")
    public String addToBasket(@RequestParam Long beverageId, HttpSession session) {
        Beverage beverage = beverageService.getBeverageById(beverageId);

        OrderItem orderItem = new OrderItem();
        orderItem.setBeverage(beverage);
        orderItem.setPrice(beverage.getPrice());

        // Retrieve the current basket from the session or create a new one
        List<OrderItem> basket = (List<OrderItem>) session.getAttribute("basket");
        if (basket == null) {
            basket = new ArrayList<>();
        }

        // Add the new OrderItem to the basket
        basket.add(orderItem);

        // Save the updated basket back into the session
        session.setAttribute("basket", basket);

        return "redirect:/basket";  // Redirect to the basket page to view the updated contents
    }

    @PostMapping("/submit-order")
    public String submitOrder(HttpSession session, Model model) {
        List<OrderItem> basket = (List<OrderItem>) session.getAttribute("basket");

        if (basket != null && !basket.isEmpty()) {
            // Create a new Order and set total price, etc.
            Order order = new Order();
            double totalPrice = 0;
            for (OrderItem item : basket) {
                totalPrice += item.getPrice(); // Calculate total price for the basket
            }
            order.setPrice(totalPrice); // Set the price of the order

            // Save the order
            orderService.saveOrder(order);

            // Associate OrderItems with the Order
            for (OrderItem item : basket) {
                item.setOrder(order); // Link each item to the order
                orderItemService.saveOrderItem(item); // Save the OrderItem
            }

            // Remove the basket from the session
            session.removeAttribute("basket");

            // Add order details to the model for the confirmation page
            model.addAttribute("totalPrice", totalPrice);  // Pass total price to the view
            model.addAttribute("orderItems", basket);  // Pass order items to the view
        }

        return "order-confirmation"; // Redirect to the order confirmation page
    }

    @PostMapping("/update-basket")
    public String updateBasket(@RequestParam Long itemId, @RequestParam int quantity, HttpSession session, HttpServletRequest request) {
        // Debugging: Print received itemId and quantity
        System.out.println("Received itemId: " + itemId + ", quantity: " + quantity);

        // Invalidate the current session and create a new one to avoid any session inconsistencies
        session.invalidate(); // Clears the current session
        session = request.getSession(true); // Creates a new session

        // Retrieve the basket from session
        List<OrderItem> basket = (List<OrderItem>) session.getAttribute("basket");

        if (basket != null && !basket.isEmpty()) {
            // Look for the OrderItem by id
            for (OrderItem item : basket) {
                System.out.println("Checking item with ID: " + item.getId());

                if (item.getId() != null && item.getId().equals(itemId)) {
                    // Found the correct item, update its quantity and price
                    item.setQuantity(quantity);
                    item.setPrice(item.getBeverage().getPrice() * quantity);

                    // Debugging: print updated item details
                    System.out.println("Updated item: " + item.getId() + ", Quantity: " + item.getQuantity() + ", Price: " + item.getPrice());
                    break;
                }
            }

            // Save the updated basket back into the session
            session.setAttribute("basket", basket);
        }

        // Redirect back to the basket page to reflect the changes
        return "redirect:/basket";
    }

    @PostMapping("/remove-item")
    public String removeItem(@RequestParam Long itemId, HttpSession session) {
        List<OrderItem> basket = (List<OrderItem>) session.getAttribute("basket");
        if (basket != null) {
            basket.removeIf(item -> item.getId().equals(itemId)); // Remove item by itemId
            session.setAttribute("basket", basket); // Save updated basket in session
        }
        return "redirect:/basket"; // Redirect back to basket page
    }
}

This is the BasketController.java file where I am defining the logic.

basket.html:

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org" lang="en">
<head>
    <meta charset="UTF-8">
    <title>Your Basket</title>
</head>
<body>
<h1>Your Basket</h1>

<!-- Empty Basket Check -->
<div th:if="${#lists.isEmpty(items)}">
    <p>Your basket is empty. Add some beverages to your basket first.</p>
</div>

<!-- Display Items -->
<

<!-- Loop through each item in the basket -->
Basket.html Form
Ensure your form is correctly structured. Specifically, ensure that the input fields for itemId and quantity are correctly named and bound:

html
Copy code
<div th:each="item : ${items}">
    <p th:text="'Beverage: ' + ${item.beverage.name}"></p>
    <p th:text="'Price: €' + ${#numbers.formatDecimal(item.price, 2, 1)}"></p>
    <p th:text="'Volume: ' + ${item.beverage.volume} + 'L'"></p>

    <!-- Form to update quantity -->
    <form action="/update-basket" method="post">
        <input type="hidden" th:value="${item.id}" name="itemId" /> <!-- Ensure itemId is passed -->
        <label for="quantity">Quantity</label>
        <input type="number" id="quantity" name="quantity" th:value="${item.quantity}" min="1" />
        <button type="submit">Update Quantity</button>
    </form>

    <!-- Form to remove item -->
    <form action="/remove-item" method="post">
        <input type="hidden" th:value="${item.id}" name="itemId" />
        <button type="submit">Remove</button>
    </form>
</div>


<!-- Display Total Price -->
<div>
    <p th:text="'Total Price: €' + ${#numbers.formatDecimal(totalPrice, 2, 1)}"></p>
</div>
<!-- Submit Order Button -->
<form action="/submit-order" method="post">
    <button type="submit">Place Order</button>
</form>

</body>
</html>

and the OrderItem.java model class:

package com.example.test1.model;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.ManyToOne;
import jakarta.persistence.JoinColumn;

@Entity
public class OrderItem {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String position;

    private double price;

    private int quantity = 1; // Default quantity

    @ManyToOne
    @JoinColumn(name = "beverage_id")
    private Beverage beverage; // This is the reference to the Beverage entity

    @ManyToOne
    @JoinColumn(name = "order_id")
    private Order order; // The order to which this item belongs

    // Getters and Setters

    public int getQuantity() {
        return quantity;
    }

    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getPosition() {
        return position;
    }

    public void setPosition(String position) {
        this.position = position;
    }

    public double getPrice() {
        return price * quantity; // Return price based on quantity
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public Beverage getBeverage() {
        return beverage;
    }

    public void setBeverage(Beverage beverage) {
        this.beverage = beverage;
    }

    public Order getOrder() {
        return order;
    }

    public void setOrder(Order order) {
        this.order = order; // Set the order for the order item
    }
}

There are also some other model classes and controllers in my project but I think for understanding the problem these should be sufficient. Why the id is being returned as null?