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

11.5 The Validator and JSP Custom Tags

Several JSP custom tags included within the Struts tag libraries can
be used with the Validator framework. One of the tags is
used to generate dynamic JavaScript based on the validation rules.
The other tags are part of the core Struts framework and are used
both with and without the Validator.

The tags listed in Table 11-4 are generic and can
be used with or without the Validator framework, but they all come in
handy when using it.

Errors

ErrorsExist

Messages

MessagesExist

The tags in Table 11-4 allow JSP pages to detect
and obtain access to messages or errors that were detected in the
Struts application. These tags were discussed in more detail in Chapter 8.

11.5.1 Using JavaScript with the Validator

The Validator framework is also capable of
generating JavaScript for your Struts application using the same
framework as for server-side validation. This is accomplished by
using a set of JSP custom tags designed specifically for this
purpose.

11.5.1.1 Configuring the validation-rules.xml file for JavaScript

The Validator custom tag called JavascriptValidator is
used to generate client-side validation based on a
javascript attribute being present within the
validator element. Before the JSP custom tag can
be used, there must be a javascript element for
the validation rule. The following code fragment illustrates the
required validation rule that includes a
javascript element:

<validator 
name="required"
classname="org.apache.struts.util.StrutsValidator"
method="validateRequired"
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.required">
<javascript><![CDATA[
function validateRequired(form) {                                                                       
var bValid = true;
var focusField = null;
var i = 0;                                                                                          
var fields = new Array( );                                                                           
oRequired = new required( );                                                                         
for (x in oRequired) {                                                                              
if ((form[oRequired[x][0]].type == 'text' || 
form[oRequired[x][0]].type ==    'textarea' ||
form[oRequired[x][0]].type == 'select-one' || 
form[oRequired[x][0]].type == 'radio' || 
form[oRequired[x][0]].type == 'password') && 
form[oRequired[x][0]].value == '') {
if (i == 0)
focusField = form[oRequired[x][0]]; 
fields[i++] = oRequired[x][1];
bValid = false;                                                                             
}                                                                                               
}                                                                                                   
if (fields.length > 0) {
focusField.focus( );
alert(fields.join('\n'));                                                                      
}                                                                                                   
return bValid;                                                                                      
}]]>
</javascript>
</validator>

When the JavascriptValidator tag is included in
the JSP page, the text from the javascript element
is written to the JSP page to provide client-side validation. When
the user submits the form, the client-side validation is executed,
and any validation rules that fail present messages to the user.

You will need to include the javascript tag with
the name of the ActionForm that
it's going to validate against:

<html:javascript formName="checkoutForm"/>

The formName attribute is used to look up the set
of validation rules to include as JavaScript in the page. You will
have to add an onsubmit event handler for the form
manually:

<html:form action="getPaymentInfo" onsubmit="return validateCheckoutForm(this);">

When the form is submitted, the validateCheckoutForm(
) JavaScript function will be invoked. The validation rules
will be executed, and if one or more rules fail, the form will not be
submitted. The javascript tag generates a function
with the name validateXXX(), where
XXX is the name of the
ActionForm. Thus, if your
ActionForm is called
checkoutForm, the javascript
tag will create a JavaScript function called
validateCheckoutForm() that executes the
validation logic. This is why the onsubmit()
event handler called the validateCheckoutForm()
function.

By default, the JavascriptValidator tag generates both static and dynamic JavaScript functions. If you would like to include a separate file that contains static JavaScript functions to take advantage of browser caching or to better organize your application, you can use the dynamicJavascript and staticJavascript attributes. By default, both of these are set to true. You can set the staticJavascript attribute to false in your form and include a separate JavaScript page with the dynamicJavascript attribute set to false and the staticJavascript attribute set to true. See the documentation for the JavascriptValidator tag for more information.