Enterprise Beans

Enterprise beans are the Java EE server side components that run inside the ejb container and encapsulates the business logic of an enterprise application. Enterprise applications are the software applications developed intended to use at large scale. These applications involves large number of data accessing concurrently by many users. Enterprise beans are used to perform various types of task like interacting with the client, maintaining session for the clients retrieving and holding data from the database and communicating with the server.

Benefits of enterprise beans: Enterprise beans are widely used for developing large and distributed applications. EJB container provides the system-level services (like transaction management and security authorization) to the enterprise beans. These services simplifies the development process of large and distributed applications and the developer just have to concentrate on solving the problem occurred in it.

The client developer can focus only on the representation style of the client as all the business logic of the application is contained in the enterprise beans. The client developer does not bother about the code that implements business logic or the logic to access the databases. This means that the clients  are thinner. It benefits the client to be thin because the client runs on the small devices.

Developing new applications from the existing beans is much easier because the enterprise beans are portable components. That means applications developed by using the enterprise components can run on any complaint J2EE server.

When to use the enterprise beans: Some of the points are illustrated below that signifies the use of enterprise beans.

• Applications developed by using the enterprise beans deal with a variety of clients, simply by writing few lines of code, so that the client can locate the enterprise beans. The client locating the enterprise bean may be various, numerous and thin.
  
• Enterprise beans support transaction to ensure the integrity of the database. Transaction is the mechanism of managing the concurrent access of shared objects.
  
• Managing the fast growing number of users requires distributed application components across multiple machines means that the application must be scalable.

Types of enterprise beans: EJB 3.0 defines two types of enterprise beans. These are:

1. Session bean: These types of beans directly interact with the client and contains business logic of the business application.
   
2. Message driven bean: It works like a listener or a consumer for a particular messaging service such as Java Message API or JPA for short.