Use this topic to explore the key concepts pertaining to Enterprise
JavaBeans (EJB) applications. Based on the EJB specification, enterprise beans
are managed Java components that typically implement the business logic of
Java 2 Platform, Enterprise Edition (J2EE) applications, as well
as access data.
- Enterprise beans
- An enterprise bean is a managed Java component that can be combined with
other resources to create Java applications. There are three types of enterprise
beans: entity beans, session beans, and message-driven beans. Enterprise beans
focus on managing business logic, providing ways to compose business logic
and declaring the transaction and security needs of business logic.
- EJB modules
- An EJB module is used to assemble one or more enterprise beans into a
single deployable unit. An EJB module is stored in a standard Java archive
(JAR) file.
- EJB containers
- An EJB container provides a run-time environment for enterprise beans
within the application server. The container handles all aspects of an enterprise
bean's operation within the application server and acts as an intermediary
between the user-written business logic within the bean and the rest of the
application server environment. Container-managed persistence (CMP) transfers
data between the variables of an entity bean and a resource manager administered
by the entity bean container.
- Partial column updates for container managed persistence
- Sequence grouping for container-managed persistence
- After assembling an EJB module that contains CMP beans, you can prevent
certain types of database-related exceptions from occurring during application
run time. Using sequence grouping, you can specify the order in which entity
beans update relational database tables.
- Message-driven beans - automatic message retrieval
- WebSphere Application Server supports the use of message-driven beans
as asynchronous message consumers.
- Message-driven beans - listener port components
- The WebSphere Application Server support for message-driven beans deployed
against listener ports is based on Java Message Service (JMS) message listeners
and the message listener service, and builds on the base support for JMS.
- Lightweight local operational mode for entity beans
- WebSphere Application Server provides a special operational mode called
lightweight local mode, which can improve the performance of entity bean methods.
You can decide which entity beans in your application to run in this mode.
- (CMP 2.x persistence only) Access intent policies
- An access intent policy is a named set of properties (access intents)
that governs data access for EJB persistence. You can assign policies to an
entity bean and to individual methods on an entity bean's home, remote, or
local interfaces during assembly. You can set access intents only within EJB
Version 2.x-compliant modules for entity beans with CMP Version 2.x.
- (CMP 2.x persistence only) Access intent service
- Access intent is a WebSphere Application Server runtime service that enables
you to more precisely manage an application's persistence.