Aim:HTTP is a stateless protocol. Session is required to maintain the state. The user may add some items to cart from the catalog page. He can check the cart page for items. He may visit catalogue again and select some more items. Here our interest is the selected items should be added to older cart rather than new cart.

PROGRAM:

Catalogue.java

import java.io.IOException;import java.io.PrintWriter;import java.util.ArrayList;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class Catalogue extends HttpServlet{ int itemcount=0; @Overridepublic void init(ServletConfig config) throwsServletException{ super.init(config);} @Overridepublic void service(HttpServletRequestreq,HttpServletResponse res) throwsIOException,ServletException{ res.setContentType("text/html");PrintWriter pw=res.getWriter();HttpSession hs=req.getSession();ArrayList cart=(ArrayList)hs.getAttribute("cart");if(cart!=null){ itemcount=cart.size();} pw.println("Select items in cart");pw.println("Catalogue"+ ""+ "XML Bible
");pw.println("Artificial Intelligence: A Modern Approach
");pw.println("Beginning Java 2
");pw.println("HTML5: Up and Running
");pw.println("");pw.println("");}}Cart.java

import java.io.IOException;import java.io.PrintWriter;import java.util.ArrayList;import java.util.Iterator;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class Cart extends HttpServlet{ @Override public void init(ServletConfig config) throws ServletException{ super.init(config);} @Override public void service(HttpServletRequestreq,HttpServletResponse res) throwsIOException,ServletException{ res.setContentType("text/html");PrintWriter pw=res.getWriter();HttpSession hs=req.getSession();ArrayList cart=(ArrayList)hs.getAttribute("cart");if(cart==null){ pw.println("No items in your cart");cart=new ArrayList();hs.setAttribute("cart",cart);} String itemselected[];String item;itemselected=req.getParameterValues("book");if(itemselected!=null){ for(int i=0;i