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

11.4 Creating Your Own Validation Rules

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:

1. Create a Java class that contains the validation methods.

2. Edit the validation-rules.xml file or create
   your own version. If you do create a new validation resource file, be
   sure to add it to the list of resource files in the Validator
   plug-in.

3. Use the new validation rules in the
   validation.xml file for your application.

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 lists the arguments for the
validateXXX() method.

Object

ValidatorAction

Field

ActionErrors

HttpServletRequest

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.

Example 11-3. A validation rule that validates a boolean value

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 ( result == null ){
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>