J2EE Design Patterns

Abstracting Business Logic

The last few chapters explored ways to keep the presentation tier and the business tier separate. We accomplished this by wrapping the domain logic for the system in both regular and Enterprise JavaBeans and introducing various controller patterns, including the MVC and Service to Worker patterns, in order to mediate the interaction between the tiers. This decoupling makes the overall system easier to understand and maintain. But without a good way to communicate between the tiers, the advantages can quickly be lost. The Business Delegate and Business Delegate Factory patterns provide client-side objects that flexibly connect the presentation and business tiers.

Business Delegate

In an MVC design, the controller still has to interact directly with the business tier (the model). The view will do so as well, although in a read-only fashion and mediated through the controller. This exposes the underlying implementation details of the business tier to the presentation tier. The application needs to know enough about the business tier to perform the operations requested by the client, and enough about the networking infrastructure between the presentation tier and the business tier to locate the business objects in the first place. The result is a tightly coupled application.

The Business Delegate pattern defines a client-side object that handles communications with the business objects. It fulfills the model role in an MVC framework. The business delegate doesn’t ...