Summary

This chapter has introduced four sets of concepts:

• The concept of Application Profile and Access Intent were introduced. We learned that access intent describes how backend resource managers are used, ensuring effective use of those backend resources, and ensuring that those resource managers are not bottlenecks in the overall application architecture. Application Profile becomes the carrier for Access intent information and lets us dynamically decide, at any desired level of an application architecture, which of the possible access intents should be used downstream. The combination of these two concepts provides significant flexibility and once again should encourage and enable the creation of reusable components. A number of ways to start or approach this powerful combination of features was provided.

• The support provided for mapping CMP entities down to relational tables was described. We learned that there are a number of options to consider. Advanced capabilities that enable supporting multiple backends and inheritance patterns are just a couple of examples of what was covered.

• The Dynamic Query Service and its related capabilities extend the idea of EJB QL, providing a rich set of capabilities for dealing with CMP 2.0 entity beans. Component reuse is more achievable with functions like this, and more efficient programming is likely. This is because very precise queries can be specified that require very little result set processing. After the query, you can just use the beans (or the data) to do business.

• Finally, this chapter introduced some Unit-of-Work concepts that go beyond the current specifications. In fact, WebSphere goes to great lengths to specify what occurs, transactionally speaking, when the EJB unspecified context is used. The prevalence of resource managers that work in this manner and the possible gains in performance provide the incentive. Advanced features such as ActivitySessions and Last Participant Support further complement the transactional capabilities of WebSphere and provide fine-grained declarative or programmatic control over units of work running the system. ActivitySessions have the additional benefit of being able to allow the EJB container to more efficiently cache EJBs.

The capabilities discussed in this chapter that are provided in the base WebSphere Application Server and those capabilities that are reserved for the Enterprise Edition are listed here:

Capability	WebSphere Application Server	WebSphere Application Server Enterprise Edition
Application Profile	None	Supports Application Profile runtime service and associated assembly tool capabilitiy.
Access Intent	Supports a static assignment of a default set of seven different Access Intent policies to an entity bean. If one of the default policies is not chosen in the AAT, the default of Pessimistic Update with weakest lock at load (wsPessimisticUpdate-WeakestLockAtLoad) is used.	Supports dynamic assignment of Access Intent policies by leveraging application profile. Supports creation of new Access Intent policies to enable customized policies beyond the seven provided.
CMP Field Mapping	Creation of the maps is via WSAD and execution is via the runtime.	No additional support provided in Enterprise Edition.
Dynamic Query	None	Supports full dynamic query.
Query Extensions	Extensions for static queries including string comparison, scalar functions, ORDER BY, SQL date/time expressions, inheritance, subqueries, EXISTS predicate, and value object access.	Extensions for dynamic queries including bean methods, dependent value methods, and multiple element SELECT clauses.
Local Transactions	Support for JCA and JDBC-based local transactions to define what goes on when the transaction context in unspecified per the EJB 2.0 specification.	ActivitySession service actually provides additional control over local transactions.
ActivitySession Service	None	Supports bean-managed and container-managed ActivitySessions for both unit of work control and to assist in retaining contained EJBs in the EJB container for durations beyond transaction.

The combination of these four sets of concepts, all provided by the WebSphere Version 5.0 runtime, provides for a lot of possibilities when it comes to leveraging EJB 2.0 beans and CMP beans in particular as part of sophisticated J2EE applications.