Add paging to dynamically created table.

Thank you for the nice code but I get the following error :

java.lang.NumberFormatException: For input string: "start=4"

Here is the complete code of the page :

<%--
    Document   : category
    Created on : May 21, 2010, 12:20:23 AM
    Author     : tgiunipero
--%>


<div id="categoryLeftColumn">

    <c:forEach var="category" items="${categories}">

        <c:choose>
            <c:when test="${category.name == selectedCategory.name}">
                <div class="categoryButton" id="selectedCategory">
                    <span class="categoryText">
                        ${category.name}
                    </span>
                </div>
            </c:when>
            <c:otherwise>
                <a href="category?${category.id}" class="categoryButton">
                    <span class="categoryText">
                        ${category.name}
                    </span>
                </a>
            </c:otherwise>
        </c:choose>

    </c:forEach>

</div>

<div id="categoryRightColumn">

    <p id="categoryTitle">${selectedCategory.name}</p>
    
    <c:set var="totalCount" scope="session" value="${fn:length(categoryProducts)}"/>
    <c:set var="perPage" scope="session"  value="4"/>
    <c:set var="pageStart" value="${param.start}"/>
    <c:if test="${empty pageStart or pageStart < 0}">
       <c:set var="pageStart" value="0"/>
    </c:if>
    <c:if test="${totalCount < pageStart}">
       <c:set var="pageStart" value="${pageStart - 4}"/>
    </c:if>
        <a href="?start=${pageStart - 4}"><<</a>${pageStart + 1} - ${pageStart + 4} <a href="?start=${pageStart + 4}">>></a>

    <table id="productTable">

        <c:forEach var="product" items="${categoryProducts}" varStatus="iter"
                   begin="${pageStart}" end="${pageStart + perPage - 1}">

            <tr class="${((iter.index % 2) == 0) ? 'lightBlue' : 'white'}">
                <td>
                    <img src="${initParam.productImagePath}${product.name}.png"
                         alt="${product.name}">
                </td>

                <td>
                    ${product.name}
                    <br>
                    <span class="smallText">${product.description}</span>
                </td>

                <td>&euro; ${product.price}</td>

                <td>
                    <form action="addToCart" method="post">
                        <input type="hidden"
                               name="productId"
                               value="${product.id}">
                        <input type="submit"
                               name="submit"
                               value="add to cart">
                    </form>
                </td>
            </tr>

        </c:forEach>

    </table>
</div>

Select allOpen in new window

There is also an underlying servlet.
Your code produces the following url :
http://localhost:8080/AffableBean/category?start=4

And the underlying controller servlet cannot handle this.
Here is the code of the controller servlet :

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package controller;

import cart.ShoppingCart;
import entity.Category;
import entity.Product;
import java.io.IOException;
import java.util.Collection;
import java.util.Map;
import javax.ejb.EJB;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import session.CategoryFacade;
import session.OrderManager;
import session.ProductFacade;
import validate.Validator;

/**
 *
 * @author tgiunipero
 */
@WebServlet(name = "Controller",
            loadOnStartup = 1,
            urlPatterns = {"/category",
                           "/addToCart",
                           "/viewCart",
                           "/updateCart",
                           "/checkout",
                           "/purchase",
                           "/chooseLanguage"})
public class ControllerServlet extends HttpServlet {

    private String surcharge;

    @EJB
    private CategoryFacade categoryFacade;
    @EJB
    private ProductFacade productFacade;
    @EJB
    private OrderManager orderManager;

    @Override
    public void init(ServletConfig servletConfig) throws ServletException {

        super.init(servletConfig);

        // initialize servlet with configuration information
        surcharge = servletConfig.getServletContext().getInitParameter("deliverySurcharge");

        // store category list in servlet context
        getServletContext().setAttribute("categories", categoryFacade.findAll());
    }

    /**
     * Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        String userPath = request.getServletPath();
        HttpSession session = request.getSession();
        Category selectedCategory;
        Collection<Product> categoryProducts;

        // if category page is requested
        if (userPath.equals("/category")) {

            // get categoryId from request
            String categoryId = request.getQueryString();

            if (categoryId != null) {

                // get selected category
                selectedCategory = categoryFacade.find(Short.parseShort(categoryId));

                // place selected category in session scope
                session.setAttribute("selectedCategory", selectedCategory);

                // get all products for selected category
                categoryProducts = selectedCategory.getProductCollection();

                // place category products in session scope
                session.setAttribute("categoryProducts", categoryProducts);
            }


        // if cart page is requested
        } else if (userPath.equals("/viewCart")) {

            String clear = request.getParameter("clear");

            if ((clear != null) && clear.equals("true")) {

                ShoppingCart cart = (ShoppingCart) session.getAttribute("cart");
                cart.clear();
            }

            userPath = "/cart";


        // if checkout page is requested
        } else if (userPath.equals("/checkout")) {

            ShoppingCart cart = (ShoppingCart) session.getAttribute("cart");

            // calculate total
            cart.calculateTotal(surcharge);

            // forward to checkout page and switch to a secure channel


        // if user switches language
        } else if (userPath.equals("/chooseLanguage")) {
            // TODO: Implement language request

        }

        // use RequestDispatcher to forward request internally
        String url = "/WEB-INF/view" + userPath + ".jsp";

        try {
            request.getRequestDispatcher(url).forward(request, response);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }


    /**
     * Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        String userPath = request.getServletPath();
        HttpSession session = request.getSession();
        ShoppingCart cart = (ShoppingCart) session.getAttribute("cart");
        Validator validator = new Validator();

        // if addToCart action is called
        if (userPath.equals("/addToCart")) {

            // if user is adding item to cart for first time
            // create cart object and attach it to user session
            if (cart == null) {

                cart = new ShoppingCart();
                session.setAttribute("cart", cart);
            }

            // get user input from request
            String productId = request.getParameter("productId");

            if (!productId.isEmpty()) {

                Product product = productFacade.find(Integer.parseInt(productId));
                cart.addItem(product);
            }

            userPath = "/category";


        // if updateCart action is called
        } else if (userPath.equals("/updateCart")) {

            // get input from request
            String productId = request.getParameter("productId");
            String quantity = request.getParameter("quantity");
            
            boolean invalidEntry = validator.validateQuantity(productId, quantity);
            
            if (!invalidEntry)
            {
                Product product = productFacade.find(Integer.parseInt(productId));
                cart.update(product, quantity);
            }
            
            userPath = "/cart";


        // if purchase action is called
        } else if (userPath.equals("/purchase")) {
            //Implement purchase action
            if (cart != null)
            {
                //extract user data from request
                String name = request.getParameter("name");
                String email = request.getParameter("email");
                String phone = request.getParameter("phone");
                String address = request.getParameter("address");
                String cityRegion = request.getParameter("cityRegion");
                String ccNumber = request.getParameter("creditcard");
                
                //validate user data
                boolean validationErrorFlag = false;
                validationErrorFlag = validator.validateForm(name, email, phone, address, cityRegion, ccNumber, request);
                
                //if validation error found, return user to checkout
                if (validationErrorFlag == true)
                {
                    request.setAttribute("validationErrorFlag", validationErrorFlag);
                    userPath = "/checkout";
                }
                else    //otherwise, save order to database
                    {
                
                    int orderId = orderManager.placeOrder(name, email, phone, address, cityRegion, ccNumber, cart);
                
                        //if order processed successfully send user to confirmation page
                        if (orderId != 0)
                        {
                            //dissociate shopping cart from session
                            cart = null;
                            
                            //end session
                            session.invalidate();
                            
                            //get order details
                            Map orderMap = orderManager.getOrderDetails(orderId);
                            
                            //place order details in request scope
                            request.setAttribute("customer", orderMap.get("customer"));
                            request.setAttribute("products", orderMap.get("products"));
                            request.setAttribute("orderRecord", orderMap.get("orderRecord"));
                            request.setAttribute("orderedProducts", orderMap.get("orderedProducts"));
                            
                            userPath = "/confirmation";
                        }
                        else //otherwise, send back to checkout page and display error
                            {
                                userPath = "/checkout";
                                request.setAttribute("orderFailureFlag", true);
                            }
                    }
            }
            
        }

        // use RequestDispatcher to forward request internally
        String url = "/WEB-INF/view" + userPath + ".jsp";

        try {
            request.getRequestDispatcher(url).forward(request, response);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

}

Select allOpen in new window

Every query string that uses category.jsp is handled my the controller.
I have the same problem like before.
I believe that we must write code in the controller too.

I found a solution based on your experience.
Thank you so much.

I just changed if (categoryId != null) with

if (categoryId != null && !categoryId.startsWith("start"))

So great support!
I love you guys!
:)