Programming Jakarta Struts

Chapter 11. The Validator Framework

The Struts framework allows input validation to occur inside the ActionForm. To perform validation on data passed to a Struts application, developers must code special validation logic inside each ActionForm class. Although this approach works, it has some serious limitations. This chapter introduces David Winterfeldt’s Validator framework, which was created specifically to work with the Struts components and to help overcome some of these limitations.

The Validator allows you to declaratively configure validation routines for a Struts application without programming special validation logic. The Validator has become so popular and widely used by Struts developers that it has been added to the list of Jakarta projects and to the main Struts distribution.

The Need for a Validation Framework

Chapter 7 discussed how to provide validation logic inside the ActionForm class. The solution presented there requires you to write a separate piece of validation logic for each property that you need to validate. If an error is detected, you have to manually create an ActionError object and add it to the ActionErrors collection. Although this solution works, there are a few problems with the approach.

The first problem is that coding validation logic within each ActionForm places redundant validation logic throughout your application. Within a single web application, the type of validation that needs to occur across HTML forms is very similar. The need ...