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Chapter 1 ✦ Understanding Java and the J2EE Platform
Applets
Applets are similar to application clients, but execute within a Web browser. Initially
applets garnered extensive attention, as they were seen as a means of making Web
pages more dynamic. Most Web browsers have an embedded Java Virtual Machine
(JVM); however, the Java plugin can be used to force the browser to use a particu-
lar version of JVM.
Web components
Although the term can be misleading, Web components do not execute on the client
side. Web components are server-side components, generally used to provide the
presentation layer to be returned to a client. Two types of Web components exist:
Java Server Pages (JSPs) and Java servlets. Very basically, JSPs are similar to regular
HTML pages but contain embedded Java code while Java servlets are Java classes
that use Java’s I/O application programming interfaces (APIs) to output HTML to
the client. Both JSPs and servlets can be used to output other format types.
Server components
Server components come in the form of Enterprise JavaBeans (EJBs). EJBs execute
within a container that manages the runtime behavior of the EJB. EJBs are usually
where the business logic for an enterprise system resides.
Roles
The roles specified within the J2EE are those played during the development and
deployment cycles of an enterprise application. While the roles are distinct, in real-
ity multiple roles tend to be filled by the same organization. The following roles are
discussed in this section:
✦ J2EE product provider
✦ Application component provider
✦ Application assembler
✦ Deployer
✦ System administrator
✦ Tool provider
✦ System component provider
The J2EE product provider
A J2EE product provider is a company that provides a product that implements a
part of the J2EE specification. For example, one company may provide a product that
implements the J2EE container for EJBs, and another may provide a product that pro-
vides an implementation for a JMS server.
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