eClient 101 Customization and Integration

102 eClient 101 Customization and Integration

5.1 Introducing J2EE

J2EE stands for Java 2 Platform, Enterprise Edition. It defines a standard that

applies to all aspects of architecture and developing multi-tier server-based

applications.

J2EE applications are made up of components where each component is a

self-contained functional software unit. A component has its related classes and

files and communicates with other components.

Four types of components are defined:

򐂰 Application clients: Java programs that execute on a client machine and

access other J2EE components.

򐂰 Applets: Java components that execute on a client machine within a browser.

򐂰 Web components: Servlets and JavaServer Pages (JSP) components that

run on the server and provide the controller and view functionality.

򐂰 Enterprise JavaBeans (EJBs): Components that run on the server for

business logic and database access.

J2EE components are written in the Java programming language and are

compiled in the same way as any Java program. In addition, J2EE components

are assembled into a J2EE application, verified to be compliant with the J2EE

specification, and deployed to the J2EE server, where they are managed and

run.

To manage and run the components of a J2EE application, the J2EE server

defines four types of containers:

򐂰 Application client container, a stand-alone Java runtime environment

򐂰 Applet container, provided by the browser

򐂰 Web component container, provided by the J2EE application server

򐂰 Enterprise JavaBeans container, provided by the J2EE application server

The components use the services provided by the container either by

implementing interfaces or by calling certain APIs as defined in the J2EE

specification. J2EE components never interact with other J2EE components

directly; the interaction takes place using services provided by the containers.

Figure 5-1 on page 103 shows the components running in their containers.

Chapter 5. eClient architecture 103

Figure 5-1 J2EE components running in containers

J2EE applications benefit from the services and the scalability provided by the

J2EE servers. Because standard protocols are used, the interoperability with

other systems is ensured.

The WebSphere Studio Application Developer is an integrated development

environment for developing J2EE components as well as assembling and testing

J2EE applications. The WebSphere Application Server is a J2EE-compliant

server. It comes with the Application Assembly Tool, which can also be used to

assemble J2EE applications from existing components.

In the following section, we provide a short introduction to servlets and

JavaServer Pages (JSP) because the eClient is based on these technologies.

You need to change the JSPs and provide new servlets for the eClient

customization and integration.

If you are new to J2EE and need more information, the following steps should

help you to quickly learn everything about J2EE:

1. Download IBM WebSphere Studio Application Developer and IBM

WebSphere Application Server from:

http://www.software.ibm.com/wsdd

2. To learn the J2EE concepts and get sample codes, go to:

http://java.sun.com/j2ee/tutorial

Database

Database

Servlet JSP Page

Web Container

Web Container

J2EE Server

J2EE Server

Enterprise

Bean

Enterprise

Bean

EJB Container

EJB Container

Browser

Applet Container

Applet Container

Browser

Applet Container

Applet Container

Client Machine

Application

Client

Container

104 eClient 101 Customization and Integration

Implement, assemble and run the sample applications with the downloaded

products.

3. To learn about J2EE in a class, enroll in the course “Servlet and JSP

Development for WebSphere using WebSphere Studio Application Developer

V5.0” (course code WF311). The course catalog can be found at:

http://www.ibm.com/services/learning/us/catalog/websphere/all.html

5.1.1 What is a servlet?

A servlet is a Java programming language class used to extend the capabilities

of servers. Commonly, servlets are used to extend the applications hosted by

Web servers (HTTP servers). They are accessed via a request-response

programming model. Figure 5-2 shows how this works with the WebSphere

Application Server.

Figure 5-2 Servlet requests and responses in WebSphere Application Server

The client sends a request to the HTTP server that has a plug-in installed that

uses a configuration file to determine whether the request should be handled by

the HTTP server or the application server. Using the standard HTTP or the

secure HTTPS, the request is forwarded to the application server, which calls a

servlet to process the request. The response is returned to the client.

Embedded

HTTP server

Application Server

Application Server

Web container

Servlet

Servlet

Servlet

Web

browser

client

HTTP server

plug-in