Enterprise JavaBeans (EJB) is a Java technology introduced by Sun Microsystems for the development of distributed object-oriented applications.
EJB is named after Java's software component model, JavaBeans. JavaBeans is primarily (though not necessarily) a client-side technology which provides portable, self-contained, reusable Java components with common coding conventions for methods and interfaces.
EJBs provide the same benefits of components for development of distributed applications. The EJB specification describes a server-side component architecture for scalable, transaction-based database and e-commerce applications.
Even without EJB, Java can be used on the server through regular JavaBeans, Servlets and supporting technologies.
EJBs add value by moving server-side systems away from a two-tier client-server model, to an n-tier architecture. The goals include scalability, reusability and robustness on the server.
Enterprise JavaBeans servers reduce the complexity of developing the middle tiers ("middleware") of a J2EE system by
providing automatic support for services such as transactions, security, and database connectivity. The EJB container, typically purchased as part of a larger solution from an external vendor such as BEA, makes these services available to EJB components.
Application developers focus on business logic, not "glue". Application Server vendors and other third-party providers who implement the EJB containers worry about those services. As long as the application developers ensure their EJB components are compliant with the specification, their classes are automatically extended to include the various services.
EJB is not a stand-alone technology. Many other services and specifications support it, as outlined by some of the authors below.
Sun announced Enterprise JavaBeans in April 1997 and released the initial specification in March 1998. Sun released the updated EJB 2.0 specification in 2001, and J2EE vendors worked throughout 2001 and 2002 to make their systems fully compliant with the new specification.