NonStop Servlets for JavaServer Pages (5.0) System Administrator's Guide

Overview and Architecture

NonStop Servlets for JavaServer Pages (NSJSP) System Administrator’s Guide—525644-002

1-3

Java 2 Enterprise Edition (J2EE) Overview

This subsection summarizes the following topics:

•

The Web Container on page 1-3

•

JavaServer Pages (JSP) on page 1-4

•

The Web Application on page 1-5

•

The WEB-INF Subdirectory on page 1-6

•

The Deployment Descriptor on page 1-6

•

Web Archive (WAR) Files on page 1-6

J2EE defines the standard for developing and running applications in a multi-tier

architecture.

The iTP WebServer implementation of servlets and JSP is a key component for J2EE

compliance. For an overview of all the other components of a complete J2EE

environment, consult the Sun Microsystems J2EE website.

The J2EE architecture has two types of client: web clients and application clients.

Application clients belong to the client-server model where the “fat” client provides not

only the GUI, but also most of the application logic. Web clients, belong to a newer

three-tier model where the “thin” client (typically a browser) supplies the GUI, and a

middleware layer, on a Webserver, provides the application logic between the GUI and

the database. The middleware layer itself is now typically based on reusable

components designed in a Model-View-Controller architecture. For an introduction to

this concept, see Model-View-Controller Designs on page 1-7.

The web client model typically uses HTTP to provide a request-response relationship

between the browser and the application logic. The client Resource Locator (URL) —

for example www.company.com/index.html — consists of the domain name —

www.company.com — and the Universal Resource Identifier (URI), the name of the

resource, in this case index.html. The URI provides the context path that is used to

locate servlets (see Map Requests to Applications and Servlets

on page 3-20).

Initially, HTTP resources were static pages of text or graphics, the same resource

being served to each client request, but now the emphasis is on building and using

dynamic resources where the same resource can be dynamically modified for each

different client request. For example, consider a mailbox, where the structure and

function is the same, but the content is clearly different for each user.

Dynamic content was initially supplied by CGI, but now the more powerful and flexible

Java Servlet API and JSP programs provide logic for the new web applications.

The Web Container

For building and running web-based applications, J2EE provides a web container,

which is a Java runtime environment that has the following content: