Design
As described in the Concepts section,
local interfaces can improve the performance of an EJB-based application, but
there are trade-offs. Up-front planning is essential, taking into account deployment
scenarios, evaluating the need for component reuse, deciding which interfaces
will be local, which will be remote. Also, local and remote interfaces use different
calling semantics: remote interfaces pass parameters by value, while local interfaces
pass them by reference. Clients must be designed and built accordingly.
OTN developers identified several areas where local interfaces
could be used in the FBS 10g. In this application, AlertsBean, PreferencesBean,
TradeDetails, and PortfolioBean are targets of a container-managed relationship
with UserAccount. UserAccount is a local entity bean that has 1:N relationships
with Alerts, Preferences, TradeDetails, and Portfolio records. (For more information
about container-managed relationships, see the Using
Container-Manged Relationships tutorial.) Therefore, per the EJB specification,
the beans must expose local interfaces. They must also reside in the same EJB
JAR file. This design, in addition to meeting the requirements for container-managed
relationships, improves the performance of the application because local method
calls are generally faster than remote calls.
Other factors can influence the choice of local or remote
interfaces. In addition to container-managed relationships, beans that are tightly-coupled
logically are good candidates for local interfaces. In the FBS 10g, a Preference
bean is always associated with a User bean, so it makes sense to co-locate them
and have them enable access via local interfaces. Another factor is the type
of client. If a bean is only going to be accessed by Web components or other
beans, consider local interfaces; otherwise, implement remote interfaces because
they enable access from anywhere. Similarly, if the application design calls
for beans distributed across multiple servers, go with remote interfaces. If
you're not certain about where a bean will be deployed or how it will be accessed,
choose remote interfaces to keep your options open.
Finally, a bean can expose both remote and local interfaces,
but such implementations are rare. To watch a viewlet that shows how the FBS 10g
uses local interfaces, browse to:
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