JAVA EE: Business Delegate Design Pattern - Class and Sequence Diagram

Sunday, 8 September 2013

Business Delegate Design Pattern - Class and Sequence Diagram

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Understanding the Architecture Through UML

The Business Delegate Design Pattern decouples the presentation tier from the business tier in distributed enterprise systems. To implement this architecture effectively, developers need a firm grasp of its structural static model (the Class Diagram) and runtime dynamic interactions (the Sequence Diagram).

Class Diagram: Roles and Collaborators

The class diagram represents the building blocks that make up this structural separation:

Client: The presentation-tier class (such as a Servlet, UI controller, or JSP) that initiates requests for business operations.
BusinessDelegate: The single contact point for the client. It aggregates a reference to the lookup service and the resolved business service interface.
BusinessLookup (Service Locator): Locates and instantiates the concrete business service instance requested by the delegate.
BusinessService (Interface): A shared interface that defines business capabilities uniformly.
Concrete Business Services: Dedicated implementations (such as EJB, JMS, or web service clients) that execute business logic.

Sequence Diagram: Execution Flow Step-by-Step

The sequence diagram illustrates how messages flow between components during an end-to-end request:

Client Invokes Delegate: The client triggers a high-level task method on the BusinessDelegate.
Service Lookup: The BusinessDelegate asks the BusinessLookup service to resolve the target business component.
Service Resolution: The BusinessLookup queries the registry or cache and returns the matching BusinessService instance.
Business Execution: The BusinessDelegate executes the target method directly on the concrete BusinessService.
Result Delivery: The BusinessService executes the domain logic and passes the processed response back to the client via the delegate.

Why Use This Design?

Presentation Shielding: Front-end developers interact only with the clean delegate API, completely shielded from network protocols or complex JNDI lookups.
Caching Opportunities: The delegate can cache service references locally, dramatically reducing lookup overhead on repeated calls.
Seamless Refactoring: Backend implementations can be upgraded, migrated, or replaced with zero breaking changes to client-facing code.