Introduction

The goal of Enterprise JavaBeans (EJB) 3.0 is to simplify development of Java applications and standardize the persistence API for the Java platform. EJB 3.0 is part of the Java EE 5.0. EJB 3.0 was worked under Java Specification Request 220 (JSR-220) in the Java Community Process (JCP). Oracle was a co-lead of the specification and provided the reference implementation for EJB 3.0 Java Persistence API. Oracle TopLink Essentials is the open sourced and community version of Oracle TopLink and is the reference implementation for Java Persistence API.

EJB 3.0 specification was finalized in May 2006 and Oracle has implemented the full support for EJB 3.0 support in Oracle Application Server 10g (10.1.3.1) . TopLink Essentials is the basis for JPA Support in Oracle Application Server 10g 10.1.3.1.

In Oracle Application Server 10g 10.1.3.1 , Oracle has implemented most of the major features of EJB 3.0 final specification. This container is available for download and trial on the Oracle Technology Network. Additionally Oracle adds some value add proprietary features to make application development easier.

Key Features in Oracle Application Server 10g (10.1.3.1)

Simplified API

A key design goal of EJB 3.0 is to simplify the developer experience. In earlier versions of EJB developers frequently found difficulty working with extensive APIs and complex deployment descriptors. Oracle Application Server 10g (10.1.3.1) provides a full implementation of the simplified model defined by EJB 3.0 Public Draft.

• Simplified EJB

EJB 3.0 eliminates the need for home and component interfaces and the requirement for bean classes for implementing javax.ejb.EnterpriseBean interfaces. The EJB bean class can be a pure Java class often referred as POJO and the interface can be a simple business interface. The bean class can implement the business interface.

• Use of Annotations Instead of Deployment Descriptors

Metadata annotation is being used as an alternative to deployment descriptors. Annotations can be used to specify bean types, different attributes such as transaction or security settings, O-R mapping and injection of environment or resource references. Deployment descriptor can be used to override metadata annotations.

• Dependency Injection

The API for lookup and usage of EJB environment and resource references is being simplified and dependency injection is being used instead. Metadata annotation is being used for dependency injection.

• Enhanced Lifecycle Methods and Callback Listener Classes

Unlike previous versions of EJB, the bean developers do not have implement all unnecessary callback methods but can designate any arbitrary method as a callback method to receive notifications for life cycle events.

A callback listener class may also be used instead of callback methods being defined in the same bean class.

• Interceptors

An interceptor is a method that intercepts a business method invocation. An interceptor method may be defined in a Stateless Session Bean, Stateful Session Bean or an Message Driven Bean. An interceptor class may also be used instead of defining the interceptor method in the bean class.

• Simple JNDI lookup of EJB

Lookup of EJB has been simplified and clients do not have to create a bean instance by invoking create method on EJB and can directly invoke a method on the EJB.

Session Beans

• Simplified Session Bean

Session Beans are pure Java classes and do not have to implement javax.ejb.SessionBean interfaces. The home interface is optional. A session bean may either have a remote, local or both interfaces and these interfaces do not have to extend EJBObject or EJBLocalObject.

• Metadata Annotations

Metadata annotations are used to specify the bean or interface and run time properties of session beans. For example, a Session bean is marked with @Stateless or @Stateful to specify the bean type. Oracle Application Server 10g 10.1.3.1 has comprehensive support of metadata annotations for session beans as specified in the EJB 3.0 final specification.

• Enhanced Lifecycle methods and call back listeners

Callback listeners are supported with both Stateful and Stateless Session beans. These callback methods can be either specified using Annotations or deployment descriptor.

• Dependency Injection

Dependency injection may be used either from a stateful or stateless session beans. Developers can use either metadata annotations or deployment descriptors to inject resources, EJB context or environment entries.

• Interceptors

Interceptor methods or interceptor classes are supported with both Stateful and Stateless session beans at bean and method level. Also default interceptors are supported using deployment descriptor element.

Message Driven Beans

• Simplified MDB

Message Driven Beans do not have to implement javax.ejb.MessageDriven interface and they implement javax.jms.MessageListener interface.

• Metadata Annotations

Metadata annotation is used to specify the bean or interface and run time properties of MDBs. For example, a MDB is marked with @MessageDriven for specifying the bean type.

• Enhanced Lifecycle Methods and Call Back Listeners

Callback listeners are supported with MDBs. These callback methods can be either specified using annotations or deployment descriptor.

• Dependency Injection

Dependency injection may be used from an MDB. Developer either use a metadata annotation or deployment descriptors to inject resources, EJB context or environment entries used by an MDB.

• Interceptors

Interceptor methods or interceptor classes can be used with MDBs.

EJB3 Java Persistence API

• Simplified Entity Beans (POJO Persistence)

EJB 3.0 greatly simplifies entities and standardizes POJO persistence model. Entity Beans are concrete Java classes and do not require any interfaces. The entity bean classes support polymorphism and inheritance. Entities can have different types of relationships and container managed relationships are manually managed by developers.

• Entity Manager API

EJB 3.0 introduces EntityManager API that is used to create, find, remove and update entities.

The EntityManager API introduces the concept of detachment/merging of entity bean instances similar to Value Object Pattern. An bean instance may be detached and may be updated by a client locally and then sent back to the EntityManager to be merged/synchronized with the database.

Oracle Application Server 10g 10.1.3.1 has comprehensive support of EntityManager API both inside and outside the EJB container.

• Metadata Annotations

Metadata annotations greatly simplify development of entities by removing the requirement of deployment descriptors. The Entity annotation is used to specify a class to be an entity bean. Annotations are used to specify transaction attributes, security permissions, callback listeners and annotated queries.

Oracle Application Server 10g 10.1.3.1 supports O-R mapping specified using metadata annotations.

• Query Language Enhancements

EJB 3.0 greatly improves the query capability for entities. It enhances EJB-QL by additional additional operations such as bulk updates and deletes, JOIN operations, GROUP BY HAVING, projection and sub-queries. Also dynamic queries can be written using EJB QL. Oracle Application Server 10g 10.1.3.1 supports most enhancements of query language.

• Enhanced Lifecycle Methods and Call Back Listeners

Callback listeners are supported with entities. These callback methods can be either specified using Annotations or deployment descriptor.

• Usability Outside the Container

The EJB 3.0 persistence engine of Oracle Application Server 10g 10.1.3.1 can be used outside container.

Feature List of EJB 3.0 Available in Oracle Application Server 10g 10.1.3.1

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Summary

EJB 3.0 simplifies the J2EE component programming model and standardizes POJO persistence model for J2EE. Oracle Application Server 10g 10.1.3.1 provides one of the industry's first comprehensive and production-ready EJB 3.0 implementations.

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