Session Management in Servlets - Shopping Cart Application Readme

Table of Contents

Introduction 

• Prerequisite
• Technical Overview

Prerequisite 

To understand this sample you need to have expertise in working with Servlets.

Technical Overview 

This sample application demonstrates how a servlet application can store and manage information in the HttpSession object.  javax.servlet.http.HttpSession is an interface that provides a way to identify a user across more than one page request or visit to a web site. It also allows the user to store and  maintain state data and application data. In particular, the HttpSession interface object supports methods to add/remove objects from the session. It stores and returns standard session properties such as a session identifier and application data. These values are stored as a name-value pair. The method for storing objects in a session is setAttribute(String s, Object o), and the method for retrieving stored objects in a session is the getAttribute(String s) method.

 A session usually corresponds to one user, who may visit a site many times. The server can maintain a session in many ways such as using cookies or rewriting URLs. The session persists for a specified time period, called as timeout period, across more than one connection or page request from the user. If a user does not come back for a certain period of time, the user's session expires and the corresponding HttpSession object is removed from memory. The default timeout period for sessions is defined by the servlet container and can be obtained via the getMaxInactiveInterval method. This timeout can be changed by using the setMaxInactiveInterval. The timeout periods used by these methods is defined in seconds. If the timeout period for a session is set to -1, the session will never expire. When a session expires or invalidates, the HttpSession object and its values are removed from the system. 

For more information about the implementation details go to code support section.

Application Overview 

The sample application allows the user to browse though the available products and then create a shopping cart, update the cart with the quantity, remove the items from the cart and finally checkout the cart.

Application Design 

• Design Notes
  
  
• Code Support

Design Notes 

 Code Support

 public void addToCart(HttpServletRequest request, HttpServletResponse response) 
                                                            throws ServletException, IOException {
 
 HttpSession session = request.getSession();
 
 // Set the session time out as one minute
 session.setMaxInactiveInterval(60);

 .....................

 }

 public void addToCart(HttpServletRequest request, HttpServletResponse response) 
                                                                    throws ServletException, IOException {
  
 HttpSession session = request.getSession();
 
 String productId[] =(String[]) request.getParameterValues("ProductIds") ;

 .................

 // Get the ids of the products added to the cart 
 productIdsInCart = (ArrayList)session.getAttribute("productIdsInCart");
 
 productDetails = new ProductDetails();
 productDetails.setProductId(productId[i]);
 

 String qty = (String) request.getParameter( ("qty"+productId[i]));
 productDetails.setQuantity(Integer.parseInt( (qty==null)?"-1":qty));
 
 String price = (String) request.getParameter(("unitPrice"+productId[i]));
 
 productDetails.setUnitPrice( Float.parseFloat( ( price ==null)?"-1.0":price)); 
 
 productIdsInCart.add(productId[i]);
 
 session.setAttribute("productIdsInCart",productIdsInCart);
 
}

When the removeAttribute(java.lang.String attributeName) method is called on the session, that object is removed from the session.
The following code snippet shows how the productIds and productDetails of the shopping cart are removed from the session.

 public void checkoutCart( HttpServletRequest request, HttpServletResponse response) 
                                                                    throws ServletException, IOException { 
 
 HttpSession session = request.getSession();
 ArrayList productIdsIncart = (ArrayList)session.getAttribute("productIdsInCart");
 
 ..............

 // Remove the ids from the session
 session.removeAttribute("productIdsInCart");
 
 for (int i = 0; i < productIdsIncart.size(); i++) {
   // Remove the shopping cart items from the session 
   session.removeAttribute((String)productIdsIncart.get(i));
 }
 }

The session can be invalidated by calling session.invalidate() method. This removes all the session informations associated with the current user session. The following code is from SessionServlet.java. It invalidates the session when the user logs out.

 String actionEvent =null; 
 actionEvent=(String)request.getParameter("actionEvent");
 
 if( actionEvent !=null && actionEvent.equals("logOut") ) { 
   session.invalidate(); 
 } 

You can find more details of the code in file EditCart.java under folder src/oracle/otnsamples/servlets.
Look into the Sample Application Files section for other details.

Sample Application Files 

This section will provide a tabular listing of the sample application files, along with their respective directory locations and a description of what they do in the overall scheme of the application:

Readme file and Stylesheets

Setting up the Sample Application 

Additional References 

• Visit the Java Servelet Technology Documentation page
• Java Servlet 2.3 Specifications
• Servlet Samples on OTN site
  

We hope you find this README file helpful. Please enter your comments about this sample in the OTN Sample Code Discussion Forum.