J2EE Design Patterns

EJB Antipatterns

Our final set of antipatterns deal with Enterprise JavaBeans. EJBs are a powerful technology, but can also be complicated and heavyweight. Two of our antipatterns deal with the complexity of EJBs: the Everything Is an EJB antipattern describes when EJBs are appropriate to use at all, while the Stateful When Stateless Will Do antipattern describes when stateful session EJBs should be used. The Round-Tripping antipattern covers common performance problems in client-server applications, and often turns up when you’re using remote EJBs.

Everything Is an EJB

There is a common antipattern called the golden hammer . A golden hammer starts life as a good solution to a recurring problem—the kind of solution that design patterns are made from. Eventually, however, the golden hammer starts getting used because it is the most familiar to developers, not because it’s the best solution. Like a carpenter with only one saw, the golden hammer may get the job done, but it doesn’t give the cleanest or easiest cut.

In many cases, EJBs are just such a golden hammer. Developers—especially developers with a history of database development—tend to see entity EJBs as the solution to every problem. Need security? Create a username and password bean. Need an address? Create an address bean.

Unfortunately, EJBs are not the solution to every problem. Like any other technology (and EJBs are a complex technology, at that), EJBs have both costs and benefits. EJBs should only be used when their benefits ...