iTP Secure WebServer System Administrator's Guide (iTPWebSvr 6.0+)

Using NonStop Servlets for JavaServer Pages
(NSJSP)
iTP Secure WebServer System Administrator’s Guide—523346-002
9-5
Java 2 Enterprise Edition (J2EE) Overview
Java 2 Enterprise Edition (J2EE) Overview
This is a general introduction to J2EE concepts that enable the use of dynamic
applications to communicate over HTTP with client browsers, specifically web
containers, servlets, JSP, Java classes, and deployment descriptors.
The iTPWebServer implementation of servlets and JSP is a key component for J2EE
compliance. It will allow support for Java-based NonStop products.
For an overview of all these other components of a complete J2EE environment,
consult the Sun Microsystems J2EE website.
In the J2EE architecture there are two types of client; web clients and application
clients. Application clients belong to the client-server model where the “fat” client
provided not only the GUI, but also most of the application logic. Web clients, on the
other hand, 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 9-36.
The web client model typically uses Hypertext Transfer Protocol (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 which is used to locate servlets, see Map Requests to
Applications and Servlets on page 9-28.
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. An example could be 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
servlet API and JSP programs are used to provide logic for the new web applications.
The Web Container
For building and running web-based applications J2EE provides a web container, a
Java runtime environment with the following content:
•
The applications - Java servlets and NSJSP, class libraries, resources such as
HTML or XML documents, and images.
•
The servlet API and runtime management including initializing, invoking and
managing the servlet and JSP lifecycles.