Business Delegate

See Core J2EE Patterns, 2nd Edition for full description of this pattern and its strategies.

Problem

You want to hide clients from the complexity of remote communication with business service components.

Forces

• You want to access the business-tier components from your presentation-tier components and clients, such as devices, web services, and rich clients.
• You want to minimize coupling between clients and the business services, thus hiding the underlying implementation details of the service, such as lookup and access.
• You want to avoid unnecessary invocation of remote services.
• You want to translate network exceptions into application or user exceptions.
• You want to hide the details of service creation, reconfiguration, and invocation retries from the clients.

Solution

Use a Business Delegate to encapsulate access to a business service. The Business Delegate hides the implementation details of the business service, such as lookup and access mechanisms.

Class Diagram

Sequence Diagram

Strategies

• Delegate Proxy Strategy
• Delegate Adapter Strategy

Consequences

• Reduces coupling, improves maintainability
• Translates business service exceptions
• Improves availability
• Exposes a simpler, uniform interface to the business tier
• Improves performance
• Introduces an additional layer
• Hides remoteness

Related Patterns

• Service Locator
  The Business Delegate typically uses a Service Locator to encapsulate the implementation details of business service lookup. When the Business Delegate needs to look up a business service, it delegates the lookup functionality to the Service Locator.
• Session Façade
  For most EJB applications, the Business Delegate communicates with a Session Façade and maintains a one-to-one relationship with that facade. Typically, the developer who implements a Session Façade also provides corresponding Business Delegate implementations.
• Proxy [GoF]
  A Business Delegate can act as a proxy, providing a stand-in for objects in the business tier. The Delegate Proxy strategy provides this functionality.
• Adapter [GoF]
  A Business Delegate can use the Adapter design pattern to provide integration for otherwise incompatible systems.
• Broker [POSA1]
  A Business Delegate acts as a Broker to decouple the business-tier objects from the clients in other tiers.

Excerpted from Core J2EE Patterns, 2nd Edition. See the book for full description of the pattern including class diagrams, sequence diagrams and sample code.