Self-Service Applications using IBM WebSphere V5.0 and IBM MQSeries Integrator

96 Self-Service Applications using IBM WebSphere V5.0 and IBM MQSeries Integrator

6.1 Application structure

The Self-Service Web application can be described as a set of interactions

between a Web browser and a Web application server. The interaction begins

with an initial request from the user’s Web browser for the welcome page of the

application. All subsequent interactions are initiated by the user by clicking a

button or a link, causing a request to be sent to the Web application server. The

Web application server processes the request, dynamically generates a results

page, and then sends it back to the client along with a set of buttons and links

that will generate the next request.

6.1.1 Model-View-Controller design pattern

One problem that is sometimes seen with large application development is that

the flow of the application is hard-wired in the presentation layer implementation

itself. This makes later application flow modifications and maintenance difficult

and expensive.

The Model-View-Controller design pattern divides the presentation layer from the

application flow and logic by dividing the application into three layers:

򐂰 Model: the Model contains the core application functionality, both business

logic and data. The model is fully decoupled from the View or the Controller.

򐂰 View: the View provides the presentation of the model, in other words, how

the application looks from a user’s point of view. The View can access the

Model information but should not make any changes to the Model directly.

Any change in the Model should be passed on to the View.

򐂰 Controller: the Controller, as its name suggests, is responsible for the

application flow. It controls how the user’s input is translated into Model

interactions and how the Model is later presented to the user through the

View.

As shown in Figure 6-1 on page 97, the Model represents the application object

that implements the application data and business logic. The View is responsible

for formatting the application results and dynamic page construction. The

Controller is responsible for receiving the client request, invoking the appropriate

business logic and, based on the results, selecting the appropriate view to be

presented to the user.

A number of different types of skills and tools are required to implement various

parts of a Web application. For example, the skills and tools required to design

an HTML page are vastly different from the skills and tools required to design

and develop the business logic part of the application. In order to effectively

leverage these scarce resources and to promote reuse, we recommend

Chapter 6. Application design 97

structuring Web applications to follow the Model-View-Controller (MVC) design

pattern.

Figure 6-1 Model-View-Controller design

Many GUI-based client/server applications have been designed using the MVC

design pattern. This powerful and well-tested design pattern can be extended to

support Self-Service Web applications. Throughout this chapter, Model is often

referred to as business logic, View is referred to as page constructor or display

page, and Controller is referred to as interaction controller.

6.1.2 Struts

In a Web environment, changes in the Model cannot be passed on to the View

directly. Instead, the View has to re-query the server to discover modifications in

the state of the application. This is called MVC Model 2 or MVC 2. In this

redbook, we use a well-known implementation of the MVC 2 design pattern

called Struts. Struts is an open-source implementation of MVC 2, part of the

Jakarta project in the Apache Software Foundation. Struts is a framework that

implements the MVC 2 pattern by providing a set of classes, servlets, JSP tag

libraries, and a flexible configuration.

The core of the Struts framework is a flexible control layer based on such

standard technologies as Java servlets, JavaBeans, ResourceBundles, and

Extensible Markup Language (XML).

Struts encourages application architectures based on the Model 2 approach, a

variation of the classic Model-View-Controller (MVC) design paradigm. Struts

provides its own Controller component and integrates with other technologies to

provide the Model and the View. For the Model, Struts can interact with any

Interaction

Controller

Controller

Page

Construction

View

Business

Logic

Model

Browser client

Web Application Server