Sessions are represented by an HttpSession object. You access a session by calling the HttpServletRequest.getSession() or HttpServletRequest.getSession(boolean) method of a request object. This method returns the current session associated with this request, or, if the request does not have a session, it creates one (unless boolean argument is false).
You can associate object-valued attributes with a session by name. Such attributes are accessible by any Web component that belongs to the same Web context and is handling a request that is part of the same session.
For example, you can save shopping cart as a session attribute. This allows the shopping cart to be saved between requests and also allows cooperating servlets to access the cart. Some servlet adds items to the cart; another servlet displays, deletes items from, and clears the cart; and next servlet retrieves the total cost of the items in the cart.
public class CashierServlet extends HttpServlet { public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { // Get the user's session and shopping cart HttpSession session = request.getSession(); ShoppingCart cart = (ShoppingCart) session.getAttribute("cart"); ... // Determine the total price of the user's books double total = cart.getTotal(); ... } }
package javax.servlet.http; public interface HttpSession { public java.lang.Object getAttribute(java.lang.String name); public java.util.Enumeration getAttributeNames(); public void removeAttribute(java.lang.String name); public void setAttribute(java.lang.String name, java.lang.Object value); }
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