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In the "Coding Actions" lesson, we validated the username and password input with a few lines of Java code. Of course, in a larger application, over time, even these few lines of code can become a maintiance budenmaintenance burden.

Happily, the framework provides a validation framework that can confirm validate input "behind the scenes".

The Code

Like the mappings, validation is Validation can be described through an XML document, or using annotations. The XML document is named after the Action being validated with a "-validation" suffix. Since we would like to validate the Login Logon Action class, our document is named Logon-validation.xml.

<!DOCTYPE validators PUBLIC 
"-//OpenSymphony Group//XWork Validator 1.0.2//EN" 
"http://www.opensymphony.com/xwork/xwork-validator-1.0.2.dtd">

<validators>
    <field name="username">
        <field-validator type="requiredstring">
            <message>Username is required</message>
        </field-validator>
    </field>
    <field name="password">
        <field-validator type="requiredstring">
            <message>Password is required</message>
        </field-validator>
    </field>
</validators>

Create a file named LoginLogon-validation.xml next to the LoginLogon.java class, and paste in the code.

...

<li><a href="<s:url action="LoginLogon"/>">Sign On</a></li>
<li><a href="<s:url action="LoginLogon_input"/>">Sign On</a></li>

struts.xml

<action name="LoginLogon" class="tutorial.LoginLogon">
<action name="LoginLogon_*" method="{1}" class="tutorial.LoginLogon">

How the Code Works

To open the Login Logon form, the Welcome page refers to LoginLogon_input.

• The framework matches this reference with the LoginLogon_* action mapping.
• The "method={1}" attribute is replaced with "method=input".
• The framework invokes the input method on the Login Logon Action class.
• Since "input" is on a special list of methods that bypass validation, the validation framework is not invoked.
• The default input method returns the result code "input".
• The framework renders "LoginLogon.jsp" as the response, without any validation messages.

To submit the Login Logon form, the Login pages refers to Login Logon.

• The framework checks for a validation for the target Action class, Login Logon.
• Finding a Logon-validation.xml file, the framework creates a validation object for the class, based on the XML document.
  • Essentially, the validation is a set of Validator objects.
• The Validators are applied to the incoming properties.
• If a Validator fails, its message is added to an internal queue.
• When all the Validators have fired, if the framework sees that errors have been posted, it seeks the "input" result, without invoking the Action class.
• Otherwise, the default Action method fires. Since the input has already been validated, the "success" result code is returned.

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