Java™ Application Development on Linux - Dator

478Chapter 21Introduction to Enterprise JavaBeanstime that it is free without requiring any distribution of client informationbetween Bean instances.From the client’s perspective, the client can connect to any instance of theBean on any server at any time to get the same work done.Stateful Session BeansWhat they are. A stateful session bean is one that remembers its client betweenmethod invocations. It maintains some information between calls froma client. Because of this, a given Bean instance can only handle one client at atime, and if an instance is to be switched between clients, the informationabout the previous client must be saved so that the client’s session may berestored later.An application that is designed around stateful session beans will generallyrequire more resources than one designed around stateless session beans(described above) because each active client requires a dedicated instance ofthe Bean.Why you would use them. We think we’ve beaten the issue of the advantagesof stateless beans into the ground. But what are the advantages of astateful bean?Many types of client interaction require the bean to “remember” somethingabout the client. The classic (and, by now, almost cliché) example is aWeb-based shopping cart application. The remote interface for a statefulShoppingCart EJB might look something like this:createCartCreates a new shopping cart for the customer.addItemAdds an item to the shopping cart.delItemRemoves an item from the shopping cart.purchaseCartProcesses the cart; charges the credit card; generates pick list, shipping list,and invoice; discards cart.abandonCartDiscards the cart.