Jakarta Struts Cookbook

8.4. Validating Dependent Fields in Struts 1.2

Problem

You are using Struts 1.2 and you want to validate a field based on the value of another related field.

Solution

Use the validwhen validator. The field element in the following snippet from a validation document indicates that the zipCode is valid when the following occurs:

• The city and state properties are not null (regardless of the zipCode value).

• The zipCode is not null:

  <form name="AddressForm">
    <field property="zipCode" depends="validwhen">
        <arg key="prompt.zipCode"/>
        <var>
            <var-name>
                test
            </var-name>
            <var-value>
                (((city != null) and (state != null)) or (*this* != null))
            </var-value>
        </var>
    </field>
  <form name="AddressForm">

Discussion

The validwhen validator, available with Struts 1.2, replaces requiredif for performing cross-field validations.

Warning

The validwhen validator, like requiredif, can't be used for client-side validation, only server-side validation.

As in Recipe 8.3, the Solution shows how you would set up the validation on a form where you were retrieving a user's address. If users specify a zip code, then they can omit the city and state; otherwise, if the city or state is not specified, the zip code is required.

With validwhen, you can code a single expression that takes the place of multiple XML elements needed for requiredif. The validwhen validator is more powerful than requiredif, though it can be trickier to get the logic correct. With requiredif, your validation makes the assertion "this field is required ...