Java 3 - 2025

Week 10

Add to Cart

In shop.jsp, convert the Add to Cart hyperlink into a form with a hidden field for the product id.
Turn the hyperlink button into a form button.
Add a quantity input next to the Add to Cart button. Set the default value to 1.

<div class="d-flex justify-content-between align-items-center">
    <small class="fw-bold"><fmt:formatNumber value="${product.price}" type="currency" /></small>
    <form method="POST" action="${appURL}/add-to-cart" class=" w-75">
        <input type="hidden" name="prod_id" value="${product.id}">
        <div class="input-group">
            <div class="form-floating">
                <input type="number" min="0" class="form-control" id="quantity" name="quantity" value="1">
                <label for="quantity">Qty</label>
            </div>
            <button type="submit" class="btn btn-outline-primary btn-sm">Add to Cart</button>
        </div>
    </form>
</div>

AddToCart servlet

Create a new servlet called AddToCart. Add a doPost method. This servlet does not need a doGet method.
Get all parameters, display a flash message, and redirect back to the shop page.
Do not set any other attributes yet.

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;

import java.io.IOException;

@WebServlet("/add-to-cart")
public class AddToCart extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String prodId = req.getParameter("prod_id");
        String quantityStr = req.getParameter("quantity");

        HttpSession session = req.getSession();
        session.setAttribute("flashMessageSuccess", "Added to cart successfully");
        resp.sendRedirect(resp.encodeRedirectURL(req.getContextPath() + "/shop"));
    }
}

Get Product Stored Procedure

Create a stored procedure to get a single product by its prod_id.

CREATE PROCEDURE sp_get_product(IN p_prod_id varchar(10))
BEGIN
    SELECT prod_id, prod_name, prod_price, prod_desc
    FROM products
    WHERE prod_id = p_prod_id;
END;

Product Constructor

Create a Product constructor for shopping cart data.

// This constructor is for products in the shopping cart
public Product(String id, String name, double price, String description) {
    this.id = id;
    this.name = name;
    this.price = price;
    this.description = description;
}

Get Product Method

Create a method in the Product DAO to get a single product by its prod_id.

public static Product get(String prod_id) {
    Product product = null;
    try(Connection connection = getConnection()) {
        CallableStatement statement = connection.prepareCall("{call sp_get_product(?)}");
        statement.setString(1, prod_id);
        ResultSet resultSet = statement.executeQuery();
        if (resultSet.next()) {
            String prodId = resultSet.getString("prod_id");
            String prodName = resultSet.getString("prod_name");
            double prodPrice = resultSet.getDouble("prod_price");
            String prodDesc = resultSet.getString("prod_desc");
            product = new Product(prodId, prodName, prodPrice, prodDesc);
        }
    } catch(SQLException e) {
        throw new RuntimeException(e);
    }
    return product;
}

Add code to the main method to test this function. The Classic Doll should print.

public static void main(String[] args) {
    System.out.println(get("DOL001"));
}

AddToCart, validate product

Update the AddToCart doPost method to validate the product. If it is null, display an error message.

@WebServlet("/add-to-cart")
public class AddToCart extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String prodId = req.getParameter("prod_id");
        String quantityStr = req.getParameter("quantity");
        
        boolean errorFound = false;
        String errorMsg = "";
        Product product = ProductDAO.get(prodId);
        if(product == null){
            errorFound = true;
            errorMsg += "Invalid product\n";
        }

        HttpSession session = req.getSession();
        if(errorFound){
            session.setAttribute("flashMessageDanger", errorMsg);
        } else {
            session.setAttribute("flashMessageSuccess", "Added to cart successfully");
        }

        resp.sendRedirect(resp.encodeRedirectURL(req.getContextPath() + "/shop"));
    }
}

Clicking an Add to Cart button should display the success message.
If you edit the HTML to have a different hidden prod_id, the error message should display.

AddToCart, validate quantity

Update the AddToCart doPost method to validate the quantity. If it is not valid, display an error message.

@WebServlet("/add-to-cart")
public class AddToCart extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String prodId = req.getParameter("prod_id");
        String quantityStr = req.getParameter("quantity");

        boolean errorFound = false;
        String errorMsg = "";
        Product product = ProductDAO.get(prodId);
        if(product == null){
            errorFound = true;
            errorMsg += "Invalid product\n";
        }

        int quantity = 0;
        try {
            quantity = Integer.parseInt(quantityStr);
            if(quantity < 0){
                errorFound = true;
                errorMsg += "Quantity cannot be negative\n";
            }
        } catch (NumberFormatException e) {
            errorFound = true;
            errorMsg += "Invalid quantity";
        }

        HttpSession session = req.getSession();
        if(errorFound){
            session.setAttribute("flashMessageDanger", errorMsg);
        } else {
            session.setAttribute("flashMessageSuccess", "Added to cart successfully");
        }

        resp.sendRedirect(resp.encodeRedirectURL(req.getContextPath() + "/shop"));
    }
}

Setting a valid quantity and clicking the Add to Cart button should display the success message.
If you edit the HTML to have an invalid quantity, the error message should display.

ShoppingCart class

Create a new model class called Shopping Cart
Add one instance variable, a Map<Product, Integer>, used to associate a product with an integer (the quantity).
When adding a product, check if it exists before adding it.

import java.util.HashMap;
import java.util.Map;

public class ShoppingCart {
    // Map to associate a product to quantity
    private Map<Product, Integer> cartContents;

    public ShoppingCart() {
        cartContents = new HashMap<>();
    }
    
    // Method to add a product to a user's cart
    public void addProduct(Product product, int quantity) {
        if(product == null) {
            throw new IllegalArgumentException("Product cannot be null");
        }
        if(quantity < 1) {
            throw new IllegalArgumentException("Quantity cannot be less than 1");
        }
        contents.put(product, contents.getOrDefault(product, 0) + quantity);
    }

    // Method to view the cart contents
    public Map<Product, Integer> getCartContents() {
        return cartContents;
    }
}

Shopping Cart main method

Write a main method to test the addProduct and getCartContents methods.
Instantiate a ShoppingCart.
Get products from the DAO.
Add products and quantities to the shopping cart.
Write a loop to display all shopping cart contents.
Even though product1 and product3 are the same, they display separately.

public static void main(String[] args) {
    ShoppingCart cart = new ShoppingCart();
    Product product1 = ProductDAO.get("DOL001");
    Product product2 = ProductDAO.get("BR02");
    Product product3 = ProductDAO.get("DOL001");
    cart.addProduct(product1, 1);
    cart.addProduct(product2, 2);
    cart.addProduct(product3, 3);
    cart.getCartContents().entrySet().forEach(cartItem -> {
        Product product = cartItem.getKey();
        int quantity = cartItem.getValue();
        double price = product.getPrice();
        double totalPrice = price * quantity;
        System.out.printf("%s, Qty: %d, Price: %.2f, Total: %.2f\n", product.getName(), quantity, price, totalPrice);
    });
}

Product Class

Generate an equals and hashCode method to determine if two Product objects are equal.
Re-run the main method in the ShoppingCart class. Products 1 and 3 are now considered the same product.

@Override
public boolean equals(Object o) {
    if (o == null || getClass() != o.getClass()) return false;
    Product product = (Product) o;
    return Double.compare(price, product.price) == 0 && categoryId == product.categoryId && Objects.equals(id, product.id) && Objects.equals(name, product.name) && Objects.equals(description, product.description) && Objects.equals(vendorId, product.vendorId) && Objects.equals(vendorName, product.vendorName) && Objects.equals(categoryName, product.categoryName);
}

@Override
public int hashCode() {
    return Objects.hash(id, name, price, description, vendorId, vendorName, categoryId, categoryName);
}

AddToCart, add item to cart

Write code to get a ShoppingCart object from the session.
If the object doesn't exist, instantiate a new one.
Add the new product and quantity.
Display the success message.

HttpSession session = req.getSession();
if(errorFound){
    session.setAttribute("flashMessageDanger", errorMsg);
} else {
    ShoppingCart cart = (ShoppingCart) session.getAttribute("cart");
    if(cart == null){
        cart = new ShoppingCart();
    }
    cart.addProduct(product, quantity);
    session.setAttribute("cart", cart);
    session.setAttribute("flashMessageSuccess", "Added to cart successfully");
}

ShoppingCart getProductCount

In the ShoppingCart class, create a new method to get the total shopping cart count and total cost.
In the first example, the for-each loop uses the .values() method to loop through the Map's integers.
In the second example, the for-each loop uses the .entrySet() method to loop through the Map's products and integers.

// Method to return the total count of products in the cart
public int getTotalProductCount() {
    int total = 0;
    for (int quantity : cartContents.values()) {
        total += quantity;
    }
    return total;
}

// Method to calculate the total cost of products in the cart
public double getTotalCost() {
    double totalCost = 0.0;
    for (Map.Entry<Product, Integer> entry : cartContents.entrySet()) {
        Product product = entry.getKey();
        int quantity = entry.getValue();
        totalCost += product.getPrice() * quantity;
    }
    return totalCost;
}

top-navigation

Replace the unused search bar with a Shopping Cart button.
The icon comes from Bootstrap Icons.
The first c:if tag will display the product count if the cart attribute is set.
The second c:if tag will display and format the total cost if the cart attribute is set.

<a href="${appURL}/cart" class="btn btn-primary me-2">
    <i class="bi bi-cart"></i> 
    <c:if test="${not empty cart.totalProductCount}">${cart.totalProductCount}, </c:if> 
    <c:if test="${not empty cart.totalCost}"><fmt:formatNumber value="${cart.totalCost}" type="currency" /></c:if>
</a>

End Day 19

Cart Servlet

Create a new Cart servlet class with a doGet Method.

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet("/cart")
public class Cart extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setAttribute("pageTitle", "Cart");
        req.getRequestDispatcher("WEB-INF/ecommerce/cart.jsp").forward(req, resp);
    }
}

cart.jsp

Create a new cart.jsp file.
Add HTML to display all items in the cart, allow the user to edit the quantity, and see a summary of contents.
Update the template's background color.
Write a c:choose tag to display the cart count.

<section class="h-100 h-custom bg-secondary">

 <!-- Code omitted -->
 
    <div class="d-flex justify-content-between align-items-center mb-5">
        <h1 class="fw-bold mb-0">Shopping Cart</h1>
        <h6 class="mb-0 text-muted">
            <c:choose>
                <c:when test="${not empty cart.totalProductCount}">${cart.totalProductCount}&nbsp;${cart.totalProductCount eq 1 ? 'item' : 'items'}</c:when>
                <c:otherwise>There are no products in your cart</c:otherwise>
            </c:choose>
        </h6>
    </div>
                                    
 <!-- Code omitted -->

    <div class="pt-5">
        <h6 class="mb-0"><a href="${appURL}/shop" class="text-body"><i
                class="fas fa-long-arrow-alt-left me-2"></i>Back to shop</a></h6>
    </div>
                                    
 <!-- Code omitted -->
 
</section>

cart.jsp

Keep one of the product rows and horizontal rules.
Add a c:forEach tag to loop through each product in the cart.
- ${cart.getContents} returns the Map object
- "item" refers to an entry in the Map
- "item.key" returns the Product
- "item.value" returns the Integer
Our products don't have images. Remove that column.
Keep one of the h6 headings.
Replace the plus/minus buttons and input with a form similar to the shop page products.
Display the price and a trash can icon.
Update column widths.

<c:forEach items="${cart.cartContents}" var="item">
    <div class="row mb-4 d-flex justify-content-between align-items-center">
        <div class="col-md-6">
            <h6 class="mb-0">${item.key.name}</h6>
        </div>
        <div class="col-md-3">
            <form method="POST" action="${appURL}/cart">
                <input type="hidden" name="prod_id" value="${item.key.id}">
                <div class="input-group">
                    <div class="form-floating">
                        <input type="number" min="0" class="form-control" id="quantity" name="quantity" value="${item.value}">
                        <label for="quantity">Qty</label>
                    </div>
                    <button type="submit" class="btn btn-outline-primary btn-sm">Update</button>
                </div>
            </form>
        </div>
        <div class="col-md-2 text-end">
            <h6 class="mb-0"><fmt:formatNumber value="${item.key.price}" type="currency" /></h6>
        </div>
        <div class="col-md-1 text-end">
            <a href="#!" class="text-muted"><i class="bi bi-trash"></i></a>
        </div>
    </div>

    <hr class="my-4">
</c:forEach>

Summary Column

Use a c:if tag to only display the Summary if the cart is set.
Remove the Shipping input and replace it with Free Shipping.
- Add shipping options to exceed expectations.
Remove the Coupon Code.
- Add coupon codes to exceed expectations.
Update the button text.

<c:if test="${not empty cart}">
    <div class="p-5">
        <h3 class="fw-bold mb-5 mt-2 pt-1">Summary</h3>
        <hr class="my-4">
        
        <div class="d-flex justify-content-between mb-4">
            <h5 class="text-uppercase">subtotal</h5>
            <h5><fmt:formatNumber value="${cart.totalCost}" type="currency" /></h5>
        </div>

        <c:set var="shipping" value="0" /><%-- Remove if you add a shipping calculation to the doPost method of the Cart servlet --%>
        <div class="d-flex justify-content-between mb-4">
            <h5 class="text-uppercase mb-3">Free Shipping</h5>
            <h5><fmt:formatNumber value="0" type="currency" /></h5>
        </div>

        <hr class="my-4">

        <div class="d-flex justify-content-between mb-5">
            <h5 class="text-uppercase">Total price</h5>
            <h5><fmt:formatNumber value="${cart.totalCost + shipping}" type="currency" /></h5>
        </div>

        <button  type="button" data-mdb-button-init data-mdb-ripple-init class="btn btn-dark btn-block btn-lg"
                 data-mdb-ripple-color="dark">Check out</button>

    </div>
</c:if>

Update Cart Items

Open the ShoppingCart model. Add method called updateProduct.
Validate the product and quantity.
Use the Map's put() method to update the product's quantity.

public void updateProduct(Product product, int quantity) {
    if(product == null) {
      	throw new IllegalArgumentException("Product cannot be null");
    }
    if(quantity < 1) {
      	throw new IllegalArgumentException("Quantity cannot be less than 1");
    }
    contents.put(product, quantity);
}

Update Quantity Button

In cart.jsp, add a hidden input with an action name "update".
Call the Cart servlet's doPost method when the button is pressed.

<form method="POST" action="${appURL}/cart" class="d-flex justify-content-center align-items-end">
    <input type="hidden" name="prod_id" value="${entry.key.id}">
    <input type="hidden" name="action" value="update">
    <div class="input-group w-50">
        <div class="">
            <%-- entry.value refers to the Integer, the product quantity--%>
            <input id="quantity" min="0" name="quantity" value="${entry.value}" type="number"
                   class="form-control form-control-sm" />

        </div>
    </div>
    <button type="submit" class="btn btn-outline-primary btn-sm">Update</button>
</form>

Delete Cart Items

Open the ShoppingCart model. Add method called deleteProduct.
Validate the product and quantity.
Use the Map's containsKey() method to verify that the product exists.
Use the Map's remove() method to delete the product key.

public void deleteProduct(Product product) {
    if(product == null) {
        throw new IllegalArgumentException("Product cannot be null");
    }
    if(contents.containsKey(product)) {
        contents.remove(product);
    }
}

Delete Cart Items

In cart.jsp, convert the trash can icon into a form that makes a post request to the Cart servlet.
Add a hidden input with an action name "delete".

<form method="POST" action="${appURL}/cart" class="d-flex justify-content-center align-items-end">
    <input type="hidden" name="prod_id" value="${entry.key.id}">
    <input type="hidden" name="action" value="delete">
    <button type="submit" class="text-muted"><i class="bi bi-trash"></i></button>
</form>

Cart Servlet doPost

Create a doPost method that gets the action and prod_id parameters.
Use the product id to get the product.
Get the ShoppingCart from the session. Continue only if both exist.

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    String action = req.getParameter("action");
    String prodId = req.getParameter("prod_id");
    Product product = ProductDAO.getProduct(prodId);
    HttpSession session = req.getSession();
    ShoppingCart cart = (ShoppingCart)session.getAttribute("cart");
    if(cart != null && product != null) {
        
    }
    req.setAttribute("pageTitle", "Cart");
    req.getRequestDispatcher("WEB-INF/ecommerce/cart.jsp").forward(req, resp);
}

Cart Servlet doPost

If the user submitted the update form, validate the quantity, then call the ShoppingCart's updateProduct method.
If the user submitted the delete form, call the ShoppingCart's deleteProduct method.
Update the cart in the session.

if (action.equals("update")) {
    String quantityStr = req.getParameter("quantity");
    int quantity = 1;
    try {
        quantity = Integer.parseInt(quantityStr);
        if (quantity < 1) {
            quantity = cart.getContents().get(product);
        }
    } catch (NumberFormatException e) {
        // If error, keep whatever is in the cart
        quantity = cart.getContents().get(product);
    }
    cart.updateProduct(product, quantity);
} else if (action.equals("delete")) {
    cart.deleteProduct(product);
}
session.setAttribute("cart", cart);

2026

When a blank is favorited, their button should look different, indicating it is already favorited.

Java 3 - Week 10

By Marc Hauschildt

Java 3 - Week 10

Marc Hauschildt

Web Technologies and Computer Software Development Instructor at Kirkwood Community College in Cedar Rapids, IA.

kirkwood.edu/businessit

Java 3 - 2025

Add to Cart

AddToCart servlet

Get Product Stored Procedure

Product Constructor

Get Product Method

AddToCart, validate product

AddToCart, validate quantity

ShoppingCart class

Shopping Cart main method

Product Class

AddToCart, add item to cart

ShoppingCart getProductCount

top-navigation

End Day 19

Cart Servlet

cart.jsp

cart.jsp

Summary Column

Update Cart Items

Update Quantity Button

Delete Cart Items

Delete Cart Items

Cart Servlet doPost

Cart Servlet doPost

2026

Java 3 - Week 10

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