Basically talking about application-scope data the web tier

the type of error that occurred than using a DatastoreException. Furthermore, adding this new exception to our IStorefrontService declarations still wouldn't expose the fact that the implementation is based on EJB.

13.2.1.2 Swapping the implementation

This method should be called only once during a request, to avoid the unnecessary overhead of creating additional remote references. However, even taking care to use the same delegate throughout a request leaves us with an implementation that isn't very efficient. The next section covers some ways to improve our use of JNDI and home interfaces.

	Don't forget that you'll need to copy the JBoss client JARs to the lib directory for your web application before using your delegate. You'll also need the home and remote interface class files for the Storefront session bean in the classes directory.

delegate to store the reference in the ServletContext after doing the required JNDI lookup is a potential solution. This would prevent any additional lookups, but it would require us to make the ServletContext available to our delegate through its constructor. This one change would ripple out to our service factory, because it currently instantiates an IStorefrontService
implementation using its no-argument constructor. It would be preferable to choose a solution without such a strong tie to HTTP constructs. A more flexible approach is to apply the EJBHomeFactory pattern as a way to cache the references we need.

13.2.2.1 Implementing an EJBHomeFactory

/**
* This class implements the EJBHomeFactory pattern. It performs JNDI
* lookups to locate EJB homes and caches the results for subsequent calls.

*/
public class EJBHomeFactory {
private Map homes;
private static EJBHomeFactory singleton; private Context ctx;