Enterprise Java Beans

• A development framework for building highly scalable, robust and distributed applications
• It is deployed on Java EE compliant Application Server such as JBOSS, Web Logic etc, so also called server side component
• It allows developers to build applications with loosely coupled business components.

3 types of EJB

• Session Bean
  • It contains business logic that can be invoked by local, remote or web service client.
  • It stores data of a particular user for a single session. It can be stateful or stateless.
  • It is less resource intensive as compared to entity beans.
  • It gets destroyed as soon as user session terminates.
  • A session bean must have an interface (i.e., business interface), through which other application components can access its services.
  • There can be multiple interfaces for a session bean—one for @Local clients and one for @Remote clients.
  • The session bean class simply implements the business interface.
  • You must tell the EJB 3.0 container that this POJO class is a session bean by annotating it with the Stateless or Stateful annotations.
  • Stateful Session Bean maintains the client state across several different service requests.
  • Stateless Session Bean requests are served by a random bean instance each time.
• Message Driven
  • Like Session Bean, it contains the business logic but it is invoked by passing message.
  • It is used in context of JMS (Java Messaging Service).
  • Message Driven Beans can consumes JMS messages from external entities and act accordingly.
• Entity Bean
  • It represents persistent data storage. It encapsulates the state that can be persisted in the database.
  • User data can be saved to database via entity beans and later on can be retrieved from the database in the entity bean.
  • It is deprecated. Now, it is replaced with JPA (Java Persistent API).

EJB 3.0

• It is annotation-driven programming model. It extensively uses Java annotations.
• Annotations replace excessive XML-based configuration files and eliminate the need for the rigid component models.
• XML-based deployment descriptors and annotations can both be used to configure service-related attributes in Java EE applications.
• The two differ in that XML files are processed separately from the code, often at runtime, while annotations are compiled with the code and checked by the compiler.
• Developing the EJB Module - Developing Java EE 5 Applications

SessionBean — Jun 11, 2016 9:05:28 AM