Service Locator Pattern:
The Service Locator pattern reduces the client complexity that results from the client's
dependency on, and need to perform, lookup and creation processes, which are resource-intensive.
To eliminate these problems, this pattern provides a mechanism to abstract all dependencies and
network details into the service locator.
Business Delegate Pattern:
The Business Delegate acts as a client-side business abstraction; it provides an abstraction for,
and thus hides, the implementation of the business services. Using a Business Delegate reduces the
coupling between presentation-tier clients and the system's business services. Depending on the
implementation strategy, the Business Delegate may shield clients from possible volatility in
the implementation of the business service API. Potentially, this reduces the number of changes
that must be made to the presentation-tier client code when the business service API or its underlying
implementation changes.
Value List Handler:
The Value List Handler pattern creates a Value List Handler to control query execution functionality and
results caching. The Value List Handler directly accesses a DAO that can execute the required query.
The Value List Handler stores the results obtained from the DAO as a collection of Transfer Objects.
The client requests the Value List Handler to provide the query results as needed. The Value List Handler
implements an Iterator pattern (GoF) to provide the solution.
Conclusion
The Dynamic EJB Statefulness pattern helps model components that
exhibit both stateful and stateless behavior. A component using this
pattern delivers the performance of stateless session beans and
serves the stateful needs of clients. Clients of a component developed
using the pattern have a simple unified interface and are hidden from
the internal swap between the stateful and stateless beans. The
pattern is a natural fit with other J2EE patterns, such as Business
Delegate and Service Locator.
Resources
Swaminathan Radhakrishnan
works as a technical architect for Infosys Technologies, Ltd.
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