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EJB applications

 

IBM WAS provides broad support for enterprise beans, including the EJB 2.x specification. The EJB 2.x specification introduces a container-managed persistence (CMP) 2.0 component model, which provides a number of improvements to aid developer productivity and application performance.

 

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In addition, WAS continues to fully support enterprise beans written to the CMP 1.1 programming model and deployed in previous versions of WAS; applications can use CMP 1.1 beans, CMP 2.0 beans, or a mixture of both. CMP 1.1 beans can be directly carried forward in an EJB 1.1 ejb-jar module or may be repackaged and combined with CMP 2.0 beans in an EJB 2.x module.

Several excellent trade books that cover the latest EJB specification and the CMP persistence model are available. A good way to locate some of these is to visit your favorite online bookstore and search on the term Enterprise JavaBeans. For a more basic orientation, see Enterprise beans: Resources for learning.

 

Innovations for EJB development

For EJB 2.x modules, a feature introduced in V5 of WAS, called Access intent policies, eases the management of interactions between CMP beans and their underlying data stores. Each policy sets data access characteristics such as access type (read or update) and transaction isolation that affect the locking of resources, letting you choose the level of data integrity and performance for your application. The Integration Server product adds APIs to enable you to further customize IBM-provided access intent policies for your particular environment.

Access intent is frequently used with the function of application profiling. For example, you can configure one transaction to load an entity bean with strong update locks and configure another transaction to load the same entity bean without locks.

Sometimes when working with entity beans you might find that it is better to use the dynamic query service rather than the regular EJB query service (which can be referred to as deployment query).

Your application development can also include asynchronous messaging, which the product supports as a method of communication based on the Java Message Service (JMS) programming interface. The base JMS support enables IBM WebSphere Application Server applications to exchange messages asynchronously with other JMS clients by using JMS destinations (queues or topics). An application can explicitly poll for messages on a destination.

WAS also provides a message listener service that applications can use to automatically retrieve messages from JMS destinations for processing by message-driven beans, without the application having to explicitly poll JMS destinations. Refer to: