Enterprise Beans in JAVA

What is Enterprise Beans

A Java EE component is called an Enterprise Beans which implements the EJB technology and runs inside an EJB container. Enterprise Beans are the server side component where the application's business logic is encapsulated. The business logic can be explained as, it is line of statement called code which is written for completing the requirements of application.

What is EJB Container

EJB container is a specification within the Application Server that runs the Enterprise Beans. Services provided by the EJB container is System-level services. In such type of services it provides the transaction and security to its enterprise beans. In addition they also provides for the Resource and life cycle management, remote accessibility, concurrency control, collision etc.

Benefits of Enterprise Beans

Generally, Enterprise beans is used for creating large, distributed applications. This is because of various reasons these are as follows :

• The first reason is the services that are provided by the EJB container to enterprise beans i.e. System-level services that helps the developer to focus on solving the business problems.
• The second reason is elaborated from first reason that the bean is responsible for application's business logic not for the client. So, a client developer can focus on only its presentation.
• The third reason is enterprise bean's portability feature i.e. the enterprise beans components can be easily or conveniently portable.

When use Enterprise Java Bean?

1. Application needs Remote Access. In other words, it is distributed.
2. Application needs to be scalable. EJB applications supports load balancing, clustering and fail-over.
3. Application needs encapsulated business logic. EJB application is separated from presentation and persistent layer.

Types of Enterprise Java Bean

There are 3 types of enterprise bean in java.

Session Bean

Session bean contains business logic that can be invoked by local, remote or webservice client.

Message Driven Bean

Like Session Bean, it contains the business logic but it is invoked by passing message.

Entity Bean

It encapsulates the state that can be persisted in the database. It is deprecated. Now, it is replaced with JPA (Java Persistent API).

Session Bean

 These types of beans directly interact with the client and contains business logic of the business application.

Session bean encapsulates business logic only, it can be invoked by local, remote and webservice client.

It can be used for calculations, database access etc.

The life cycle of session bean is maintained by the application server (EJB Container).

Types of Session Bean

There are 3 types of session bean.

1) Stateless Session Bean: It doesn't maintain state of a client between multiple method calls.

2) Stateful Session Bean: It maintains state of a client across multiple requests.

3) Singleton Session Bean: One instance per application, it is shared between clients and supports concurrent access.

Stateless Session Bean

Stateless Session bean is a business object that represents business logic only. It doesn't have state (data).

In other words, conversational state between multiple method calls is not maintained by the container in case of stateless session bean.

The stateless bean objects are pooled by the EJB container to service the request on demand.

It can be accessed by one client at a time. In case of concurrent access, EJB container routes each request to different instance.

Stateful Session Bean

Stateful Session bean is a business object that represents business logic like stateless session bean. But, it maintains state (data).

In other words, conversational state between multiple method calls is maintained by the container in stateful session bean.

Message-Driven Bean :

 Message-Driven Bean permits the Java Enterprise Edition applications for processing messages asynchronously. Message-Driven beans likewise the JMS message listener, that receives the JMS messages rather than events.

Disadvantages of EJB

1. Requires application server
2. Requires only java client. For other language client, you need to go for webservice.
3. Complex to understand and develop ejb applications.