Using Validator

Validator Overview

Before getting into the details of using the Validator framework, it's necessary to give an overview of how Validator works. Recall that without Validator, you have to code all of your form data validations into the validate( ) methods of your Form Bean objects. Each Form Bean field that you want to perform a validation on requires you to code logic to do so. Additionally, you have to write code that will store error messages for validations that fail. With Validator, you don't have to write any code in your Form Beans for validations or storing error messages. Instead, your Form Beans extend one of Validator's ActionForm subclasses that provide this functionality for you.

The Validator framework is set up as a pluggable system of validation routines that can be applied to Form Beans. Each validation routine is simply a Java method that is responsible for performing a specific type of validation and can either pass or fail. By default, Validator comes packaged with several useful validation routines that will satisfy most validation scenarios. However, if you need a validation that is not provided by the framework, you can create your own custom validation routine and plug it into the framework.

Validator uses two XML configuration files to tell it which validation routines should be "installed" and how they should be applied for a given application, respectively. The first configuration file, validator-rules.xml, declares the validation routines that are plugged into the framework and assigns logical names to each of the validations. Additionally, the validator-rules.xml file is used to define client-side JavaScript code (or the location of client-side JavaScript code) for each validation routine. If configured to do so, Validator will emit this JavaScript code to the browser so that validations are performed on the client side as well as the server side. The second configuration file, validation.xml, defines which validation routines are applied to which Form Beans. The definitions in this file use the logical names of Form Beans from the Struts configuration file (e.g., struts-config.xml) along with the logical names of validation routines from the validator-rules.xml file to tie the two together.

Note 

It's important to point out that while traditionally the validator-rules.xml file stores validation routine definitions and the validation.xml file applies validation routines to Form Beans, both configuration files are governed by the same DTD. Thus their contents could technically be combined into one file.