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Building a Java servlet framework using reflection, Part 2

Gain greater functionality with less code using these reflective code samples

By Michael Cymerman, JavaWorld.com, 02/01/00

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When most developers see the word framework in this article's title, they will immediately become skeptical. I have read numerous articles that purport to describe the one-and-only best solution for Java programming -- especially on the server side. I'm not going to claim that the method outlined here is the only way to go; I merely want to show that it has been successful.

TEXTBOX: TEXTBOX_HEAD: Building a Java servlet framework using reflection: Read the whole series!

:END_TEXTBOX

In Part 1, I outlined a simple scheme through which you could use reflection in the development life cycle to reduce coding time and interdependencies. In this article, I hope to bring that high-level discussion down to specific code examples that you can use in your development projects.

It is important to note that not all applications will benefit from the same level of framework development. Because some applications require more enhanced data access or accept user input differently, some of this information will not be relevant to all of them -- especially those apps whose underlying business processes are in a constant state of flux.

The examples in this article will concern the development of:

  • Dynamically loaded business objects containing developed validation schemes
  • An error-handling hierarchy that will let you concentrate on your specific cases rather than the protection of an entire system
  • Database code that will let you interact with a database simply and efficiently
  • Presentation objects that enable you to concentrate on the logic behind the code rather than presentation mechanics


I hope you will find this article helpful. These principles have enabled my teams to develop complex systems in a short timeframe.

Recap

In Part 1, I divided a system into the three logical layers: business, data, and presentation. I will expand on each of these layers in the following sections. In addition, I'll present some error-handling code that fits into this framework.

Business objects

A business object is associated with each behavior of an application. For example, all objects built to handle forms in an application will have the behaviors of validating input, processing input, interfacing with the data access layer, and presenting output to the user. In a similar fashion, all business objects for pages reached through direct HTML links could have the behavior of analyzing the path taken by the user, data access, and output presentation.

The business object lets you concentrate on the functionality associated with each business use case, such as registering a user or buying an airline ticket. Using this scheme, you can develop business objects with decreased dependencies on the presentation layer, allowing them to undergo strenuous unit testing that is independent of the graphical interface.

Developing business objects and validation

You can load a business object reflectively, based upon the action type passed to the proxy servlet. The action type can be passed as an input parameter, a directory within the URL, or through some alias. This is left to the reader for further investigation.

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