Core J2EE Patterns - Value List Handler: "Core J2EE Patterns - Value List Handler
The client requires a list of items from the service for presentation. The number of items in the list is unknown and can be quite large in many instances.
Most Java 2 Platform, Enterprise Edition (J2EE) applications have a search and query requirement to search and list certain data. In some cases, such a search and query operation could yield results that can be quite large. It is impractical to return the full result set when the client's requirements are to traverse the results, rather than process the complete set. Typically, a client uses the results of a query for read-only purposes, such as displaying the result list. Often, the client views only the first few matching records, and then may discard the remaining records and attempt a new query. The search activity often does not involve an immediate transaction on the matching objects. The practice of getting a list of values represented in entity beans by calling an ejbFind() method, which returns a collection of remote objects, and then calling each entity bean to get the value, is very network expensive and is considered a bad practice.
There are consequences associated with using Enterprise JavaBeans (EJB) finder methods that result in large results sets. Every container implementation has a certain amount of finder method overhead for creating a collection of EJBObject references. Finder method behavior performance varies, depending on a vendor's container implementation. According to the EJB specification, a container may invoke ejbActivate() methods on entities found by a finder method. At a minimum, a finder method returns the primary keys of the matching entities, which the container returns to the client as a collection of EJBObject references. This behavior applies for all container implementations. Some container implementations may introduce additional finder method overhead by associating the entity bean instances to these EJBObject instances to give the client access to those entity beans. However, this is a poor use of resources if the client is not interested in accessing the bean or invoking its methods. This overhead can significantly impede application performance if the application includes queries that produce many matching results.
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