Enterprise JavaBeans, Third Edition

Dependent Value Classes

As discussed in the previous section, dependent value classes are custom serializable objects that can be used as persistence fields—(although this use is not recommended). Dependent value classes are useful for packaging data and moving it between an entity bean and its remote clients. They separate the client’s view of the entity bean from its abstract persistence model, which makes it easier for the entity bean class to change without impacting existing clients.

The remote interface methods of an entity bean should be defined independently of the anticipated abstract persistence schema. In other words, you should design the remote interfaces to model the business concepts, not the underlying persistence programming model. Dependent value classes can help separate a remote client’s view from the persistence model by providing objects that fill the gaps in these perspectives. Dependent value classes are used a lot in remote interfaces where packaging data together can reduce network traffic, but are less useful in local interfaces.

For example, the CustomerEJB could be modified so that its lastName and firstName fields are not exposed directly to remote clients through their accessor methods. This is a reasonable design approach, since most clients access the entire name of the customer at once. In this case, the remote interface might be modified to look as follows:

import java.rmi.RemoteException; public interface CustomerRemote extends javax.ejb.EJBObject ...