11.2. J2EE overview
J2EE is a specification for application server technology supporting the middle tiers of an application architecture. J2EE specifically addresses two tiers: the web tier and the EJB tier. The web tier contains components that service hypertext transfer protocol (HTTP) requests from web browsers and dynamically generate hypertext markup language (HTML) content in response. The EJB tier contains components that are transactional, scalable, secure, and which facilitate the encapsulation of and access to data entities. Application architectures are free to employ components from either tier or from both, as warranted by the application.
11.2.1. Enterprise JavaBeans tier
The EJB specification enables server-side application component ...