Tutorials : Putting Design Principles to the Test(A Java based Case Study) :

A Sample ReportWriter Component Case Study

Now that we have recapitulated the principles that we need to keep in mind while designing any component, let us venture to design such a component. For example, let us think that we need to develop a Reporting component. This component in short needs to support the following features:

• It will accept the criteria for producing any report.
• Against a set of valid criteria, it will fetch the data from a data source and produce the report in a desired format.

I would at this point try to avoid any detailed discussion of any other possible features that the ReportWriter component might provide.

Business Type Model

With these features in mind, we can develop a sample Business Type Model (BTM) for our ReportWriter component. This sample BTM is presented in Figure 1.

Figure 1: The Business Type Model for the ReportWriter component

This BTM shows the different components acting together to produce the report. The Client component makes a report request to the RequestHandler component. The RequestHandler component then makes a call to the ReportWriter component supplying the report parameters to it. The ReportWriter component then makes use of DAO component to obtain the data from a specific data source, produces the report and hands it over to the RequestHandler component to send it back to the appropriate client.

Designing the Classes

Once we have the BTM with us, it is time to get into the real class structure. Deciding on the class structure is often an iterative process. The initial design may get affected with slight requirement change or changes in the existing components that the component in question is going to use. In this context, the challenge is to come up with a design, which is flexible enough to accommodate such changes.

Well then, lets proceed with designing the classes for our ReportWriter component. First of all, let us consider the entry point to the ReportWriter component. A Client makes a request to the ReportWriter. We need a mechanism to handle this request. If you are developing a web-based application, this request will typically be over HTTP. So, we need to have a mechanism to handle the HTTP requests. In Java world, this is handled by using a Servlet.

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