The Validator framework is preconfigured with many of the most common rules that you’re likely to need for your Struts applications. If your application has validation requirements that are not met by the default rules, you have complete freedom to create your own. There are several steps that you must follow, however, to create your own customized rules:

Each validation method you create must have the following signature:

public static boolean validateXXX( java.lang.Object,
                                   org.apache.commons.validator.ValidatorAction,
                                   org.apache.commons.validator.Field,
                                   org.apache.struts.action.ActionErrors,
                                   javax.servlet.http.HttpServletRequest,
                                   javax.servlet.ServletContext );

where validateXXX can be whatever you want it to be, as long as it’s not a duplicate rule name. Table 11-3 explains the arguments to the validateXXX( ) method.

In most cases, the method should be static. However, you can define instance-level methods as well. Regardless of whether your methods are static, you must ensure that they are thread-safe. Example 11-3 illustrates a new validation rule that validates whether a String value is a valid boolean.

import java.io.Serializable;
import java.util.Locale;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.validator.Field;
import org.apache.commons.validator.GenericTypeValidator;
import org.apache.commons.validator.GenericValidator;
import org.apache.commons.validator.ValidatorAction;
import org.apache.commons.validator.ValidatorUtil;
import org.apache.struts.action.ActionErrors;
import org.apache.struts.util.StrutsValidatorUtil;

public class NewValidator implements Serializable {
  /**
   * A validate routine that ensures the value is either true or false.
   */
  public static boolean validateBoolean( Object bean, ValidatorAction va,
    Field field, ActionErrors errors, HttpServletRequest request ) {

    String value = null;
    // The boolean value is stored as a String

    if (field.getProperty() != null && field.getProperty().length(  ) > 0){
      value = ValidatorUtil.getValueAsString(bean, field.getProperty(  ) );
    }


    Boolean result = Boolean.valueOf(value);
    if (value == null || ! (value.equalsIgnoreCase("true") ||
                            value.equalsIgnoreCase("false")))  {
      errors.add( field.getKey(  ),
                  StrutsValidatorUtil.getActionError(request, va, field));
    }

    // Return true if the value was successfully converted, false otherwise
    return (errors.empty(  ));
  }
}

The next step is to add this new rule to the validation-rules.xml file, or to a new file to keep your customized rules separate. The validator element for the validateBoolean rule should look something like:

<validator name="boolean"
  classname="NewValidator"
  method="validateBoolean"
  methodParams="java.lang.Object,
    org.apache.commons.validator.ValidatorAction,
    org.apache.commons.validator.Field,
    org.apache.struts.action.ActionErrors,
    javax.servlet.http.HttpServletRequest"
  msg="errors.boolean">

The final step is to use the new validation rule in the validation.xml file. This involves creating a field element that matches a boolean property on an ActionForm:

<field property="sendEmailConfirmation" depends="boolean">
   <arg0 key="label.emailconfirmation"/>
</field>