Server User Manual

Table Of Contents
Chapter 2: Programming for the Java 2 Platform, Enterprise Edition 7
Why are J2EE applications desirable?
This expanded diagram shows you the various components you might find running on
the various tiers:
The client in a J2EE application can be a JavaServer Page (JSP), HTML page, or
applet running in a browser; a Java application on a desktop machine; or even a Java
client on some portable device, such as a personal digital assistant (PDA) or cell
phone.
The middle-tier can have a servlet or a JSP-generated servlet running on a web server.
These elements usually make up the server-side presentation logic. An EJB container
provides a runtime environment for Enterprise JavaBeans, which contain the
business logic of application. Both a web server and an Enterprise JavaBeans (EJB)
container provide services to the components that run on them. Because these
services are always available, programmers dont have to include them in the
components they write.
The Enterprise Information System (EIS) tier is a repository for the enterprises data.
Usually it consists of the data in a relational database system.
Few J2EE applications have all of these components. They can be mixed and matched
in very flexible ways to meet the needs of the enterprise. See Chapter 3, Creating
applications with J2EE technologies for more on this topic.