Programming Jakarta Struts, 2nd Edition [Electronic resources] نسخه متنی

11.1 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 to validate required fields, dates, times, and
numbers, for example, typically occurs in many places throughout an
application. Most nontrivial applications have multiple HTML forms
that accept user input that must be validated. Even if you use a
single ActionForm for your entire application, you
might still end up duplicating the validation logic for the various
properties.

The second major problem is one of maintenance. If you need to modify
or enhance the validation that occurs for an
ActionForm, the source code must be recompiled.
This makes it very difficult to configure an application.

The Validator framework allows you to move all the validation logic
completely outside of the ActionForm and
declaratively configure it for an application through external XML
files. No validation logic is necessary in the
ActionForm, which makes your application easier to
develop and maintain. The other great benefit of the Validator is
that it's very extensible. It provides many standard
validation routines out of the box, but if you require additional
validation rules, the framework is easy to extend and provides the
ability to plug in your own rules (again without needing to modify
your application).