Chapter 7. Enterprise JavaBeans
7.1. Introduction
7.1.1. Overview of Enterprise JavaBeans
Enterprise JavaBeans (EJB) 3.1 is an API for developing distributed, transactional, secure and portable Java EE applications through the use of server-side components called Enterprise Beans. Enterprise Beans implement the business logic of an application in a decoupled manner that encourages reuse. Enterprise JavaBeans 3.1 is documented as the Java EE specification JSR-318.
JBoss EAP 6 has full support for applications built using the Enterprise JavaBeans 3.1 specification. The EJB Container is implemented using the JBoss EJB3 community project, http://www.jboss.org/ejb3.
7.1.2. EJB 3.1 Feature Set
The following features are supported in EJB 3.1
- Session Beans
- Message Driven Beans
- No-interface views
- local interfaces
- remote interfaces
- JAX-WS web services
- JAX-RS web services
- Timer Service
- Asynchronous Calls
- Interceptors
- RMI/IIOP interoperability
- Transaction support
- Security
- Embeddable API
The following features are supported in EJB 3.1 but are proposed for "pruning". This means that these features may become optional in Java EE 7.
- Entity Beans (container and bean-managed persistence)
- EJB 2.1 Entity Bean client views
- EJB Query Language (EJB QL)
- JAX-RPC based Web Services (endpoints and client views)
7.1.3. EJB 3.1 Lite
EJB Lite is a sub-set of the EJB 3.1 specification. It provides a simpler version of the full EJB 3.1 specification as part of the Java EE 6 web profile.
EJB Lite simplifies the implementation of business logic in web applications with enterprise beans by:
- Only supporting the features that make sense for web-applications, and
- allowing EJBs to be deployed in the same WAR file as a web-application.
7.1.4. EJB 3.1 Lite Features
EJB Lite includes the following features:
- Stateless, stateful, and singleton session beans
- Local business interfaces and "no interface" beans
- Interceptors
- Container-managed and bean-managed transactions
- Declarative and programmatic security
- Embeddable API
The following features of EJB 3.1 are specifically not included:
- Remote interfaces
- RMI-IIOP Interoperability
- JAX-WS Web Service Endpoints
- EJB Timer Service
- Asynchronous session bean invocations
- Message-driven beans
7.1.5. Enterprise Beans
Enterprise beans are server-side application components as defined in the Enterprise JavaBeans (EJB) 3.1 specification, JSR-318. Enterprise beans are designed for the implementation of application business logic in a decoupled manner to encourage reuse.
Enterprise beans are written as Java classes and annotated with the appropriate EJB annotations. They can be deployed to the application server in their own archive (a JAR file) or be deployed as part of a Java EE application. The application server manages the lifecycle of each enterprise bean and provides services to them such as security, transactions, and concurrency management.
An enterprise bean can also define any number of business interfaces. Business interfaces provide greater control over which of the bean's methods are available to clients and can also allow access to clients running in remote JVMs.
There are three types of Enterprise Bean: Session beans, Message-driven beans and Entity beans.
Important
Entity beans are now deprecated in EJB 3.1 and Red Hat recommends the use of JPA entities instead. Red Hat only recommends the use of Entity beans for backwards compatibility with legacy systems.
7.1.6. Overview of Writing Enterprise Beans
Enterprise beans are server-side components designed to encapsulate business logic in a manner decoupled from any one specific application client. By implementing your business logic within enterprise beans you will be able to reuse those beans in multiple applications.
Enterprise beans are written as annotated Java classes and do not have to implement any specific EJB interfaces or be sub-classed from any EJB super classes to be considered an enterprise bean.
EJB 3.1 enterprise beans are packaged and deployed in Java archive (JAR) files. An enterprise bean JAR file can be deployed to your application server, or included in an enterprise archive (EAR) file and deployed with that application. It is also possible to deploy enterprise beans in a WAR file along side a web application if the beans comply with the EJB 3.1 Lite specification.
7.1.7. Session Bean Business Interfaces
7.1.7.1. Enterprise Bean Business Interfaces
An EJB business interface is a Java interface written by the bean developer which provides declarations of the public methods of a session bean that are available for clients. Session beans can implement any number of interfaces including none (a "no-interface" bean).
Business interfaces can be declared as local or remote interfaces but not both.
7.1.7.2. EJB Local Business Interfaces
An EJB local business interface declares the methods which are available when the bean and the client are in the same JVM. When a session bean implements a local business interface only the methods declared in that interface will be available to clients.
7.1.7.3. EJB Remote Business Interfaces
An EJB remote business interface declares the methods which are available to remote clients. Remote access to a session bean that implements a remote interface is automatically provided by the EJB container.
A remote client is any client running in a different JVM and can include desktop applications as well as web applications, services and enterprise beans deployed to a different application server.
Local clients can access the methods exposed by a remote business interface. This is done using the same methods as remote clients and incurs all the normal overhead of making a remote request.
7.1.7.4. EJB No-interface Beans
A session bean that does not implement any business interfaces is called a no-interface bean. All of the public methods of no-interface beans are accessible to local clients.
A session bean that implements a business interface can also be written to expose a "no-interface" view.
