Enterprise Java Beans (EJB)

What is EJB?
Enterprise JavaBeans (EJB) technology is the server-side component architecture for Java Platform, Enterprise Edition (Java EE). EJB technology enables rapid and simplified development of distributed, transactional, secure and portable applications based on Java technology.When compared with other distributed component technologies such as Java RMI and CORBA, the EJB architecture hides most the underlying system-level semantics that are typical of distributed component applications, such as instance management, object pooling, multiple threading, and connection pooling.

Why to use EJB?

If an application is small in scope and is not required to be highly scalable, you can use J2EE components, such as servlets, together with direct JDBC connectivity to build it. However, as the application complexity grows or the number of concurrent users increases, the use of EJBs makes it much easier to partition and scale the application. In this case, using EJBs gives you some significant advantages.

When to use EJB?
EJBs are required in the following scenarios.

i. When the application is distributed: When the resources and data are distributed across multiple sites, then it is ideal to go for an application that is based on EJBs. Choose EJB when you know your application will need to scale beyond initial low usage levels and support multiple, concurrent users.

ii. When the application is performance-centric, use of EJBs and the application server provide high performance and very good scalability.

iii. Declaratively manage transactions. When transaction management is required to ensure data integrity, EJBs may be used. In EJB, you merely specify whether a bean's methods require, disallow, or can be used in the context of a transaction. The EJB container will manage your transaction boundaries appropriately.

iv. Declaratively manage security. The EJB model allows you to indicate a security role that the user must be assigned to in order to invoke a method on a bean.

v. Separation of Business Logic. The most significant difference between a web application using only servlets and one using servlets with EJBs is that the EJB model mandates a separation between display and business logic. This can be achieved using Servlets and DAO also