Java Enterprise Best Practices

Cache JNDI Lookup Objects

To get a DataSource , or an EJB home interface, you typically create an InitialContext , and then do a lookup for the needed resource. These operations are usually very expensive, considering the fact that you perform them all the time throughout your code.

Fortunately, you can optimize these lookups fairly easily by doing the lookup only once, and then reusing the lookup result whenever you need it again—effectively caching it. This is usually done with a singleton class. The singleton can be very simple and cache only specified objects, or it can be a sophisticated service locator that caches many arbitrary objects. An extra benefit of the singleton scheme is that you centralize the Java Naming and Security Interface (JNDI) names of your objects, so if the names change, you have to change your code in only one place: the singleton class.

Example 2-8 shows a singleton that stores several EJB home objects.

Example 2-8. Using a singleton class to cache lookup objects

public class EJBHomeCache { private static EHBHomeCache instance; protected Context ctx = null; protected FirstEJBHome firstHome = null; protected SecondEJBHome secondHome = null; private EJBHomeCache( ) { try { ctx = new InitialContext( ); firstHome = (FirstEJBHome)PortableRemoteObject.narrow ( ctx.lookup ("java:comp/env/FirstEJBHome"), FirstEJBHome.class); secondHome = (SecondEJBHome)PortableRemoteObject.narrow ( ctx.lookup ("java:comp/env/SecondEJBHome"), FirstEJBHome.class); } catch ...