Introduction

This is the translation in English of my previous post.

Java EE is a programming technology for information systems based on application servers. This technology uses various types of software components managed by the application server which act like mediators between client programs and other specialized servers (e.g. database servers). While Java is a programming language, Java EE is a standard specifying, on one hand, the way of developing systems based on application servers, on the other hand the "services" that the application server must provide in order for the application to be independent of the application server. "Services" mentioned in the previous sentence should not make the reader think about Web services, the meaning intended being a more general one, that is of functions or methods that are available to the applications in the environment created by the application server. The principle "write once, run everywhere" is valid for Java EE applications as well, that is any application that conforms to the standard should run as well with Oracle WebLogic, IBM WebSphere, Sun GlassFish, etc. (the previous enumeration represents the most well-known application servers as of now).

The architecture of Java EE applications is developed in three tiers: client, application server, database, and represents an evolution of older client-server type architectures. Generally, a Java EE application can be viewed as four-tiered, because inside the application server there are two containers, one to manage Web components (JSP and JSF pages) and another to manage EJB (Enterprise JavaBeans) components.