EJB - Overview

EJB stands for Enterprise Java Beans. EJB is an essential part of a J2EE platform. J2EE platform has component based architecture to provide multi-tiered, distributed and highly transactional features to enterprise level applications.

EJB provides an architecture to develop and deploy component based enterprise applications considering robustness, high scalability, and high performance. An EJB application can be deployed on any of the application server compliant with the J2EE 1.3 standard specification.

We'll be discussing EJB 3.0 in detail in this tutorial.

Types

EJB is primarily divided into three categories; following table lists their names with brief descriptions −

S.No	Type & Description
1	Session Bean Session bean 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 bean. Session bean gets destroyed as soon as user session terminates.
2	Entity Bean Entity beans represent persistent data storage. User data can be saved to database via entity beans and later on can be retrieved from the database in the entity bean.
3	Message Driven Bean Message driven beans are used in context of JMS (Java Messaging Service). Message Driven Beans can consumes JMS messages from external entities and act accordingly.

Benefits

Following are the important benefits of EJB −

• Simplified development of large-scale enterprise level application.
• Application Server/EJB container provides most of the system level services like transaction handling, logging, load balancing, persistence mechanism, exception handling, and so on. Developer has to focus only on business logic of the application.
• EJB container manages life cycle of EJB instances, thus developer needs not to worry about when to create/delete EJB objects.
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