Java Enterprise Best Practices

Use Business Delegates for Clients

A business delegate is a plain Java class that delegates all calls to an EJB. It might seem too simple to be useful, but it’s actually commonly used. The main reason to use a business delegate is to separate the EJB handling logic (e.g., getting remote interfaces, handling remote exceptions, etc.) from the client so that developers working on the client code don’t have to know and worry about various EJB details.

Another benefit of business delegates is that you can initially leave all their business methods empty and, by doing so, give client developers something to work with so that they don’t have to wait for EJBs to be developed. It’s also not uncommon to implement straight JDBC code in the business delegate, instead of leaving it blank, in case you’d like to have a functional prototype. Even in a fully implemented J2EE application, delegates are useful for caching common client requests and computation results from the business layer.

Example 2-9 contains a business delegate that demonstrates some of the basic benefits discussed here. It delegates its calls to a remote stateless session bean that is actually a session façade, retrying several times in case of a network problem.

Example 2-9. A business delegate

public class BeanDelegate { private static final int NETWORK_RETRIES = 3; private BeanRemote bean; public void create( ) throws ApplicationError { // Here you get a bean instance. try { InitialContext ctx = new InitialContext( ); BeanHome ...