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     <h1 class="no_toc" id="form-validation-using-xml">Form Validation Using XML</h1>

 <ul id="markdown-toc">
   <li><a href="#introduction" id="markdown-toc-introduction">Introduction</a></li>
   <li><a href="#example-application" id="markdown-toc-example-application">Example Application</a></li>
   <li><a href="#validation-using-xml" id="markdown-toc-validation-using-xml">Validation Using XML</a></li>
   <li><a href="#xml-validator-format" id="markdown-toc-xml-validator-format">XML Validator Format</a></li>
   <li><a href="#validating-an-email-address" id="markdown-toc-validating-an-email-address">Validating An Email Address</a></li>
   <li><a href="#validating-a-users-input-using-a-regular-expression" id="markdown-toc-validating-a-users-input-using-a-regular-expression">Validating A User’s Input Using A Regular Expression</a></li>
   <li><a href="#validating-a-users-input-using-an-ognl-expression" id="markdown-toc-validating-a-users-input-using-an-ognl-expression">Validating A User’s Input Using An OGNL Expression</a></li>
   <li><a href="#summary" id="markdown-toc-summary">Summary</a></li>
 </ul>

 <p>The example code for this tutorial, <strong>form-xml-validation</strong>, is available for checkout at <a href="https://github.com/apache/struts-examples">struts-examples</a></p>

 <h2 id="introduction">Introduction</h2>

 <p>In this tutorial we’ll cover how to validate a user’s input in form fields using Struts 2’s XML validation methodology.
 In the <a href="form-validation">Form Validation</a> tutorial we discussed validating a user’s input using the validate method
 in the Action class. Using a separate XML validation file gives you the ability to use validators built-in
 to the Struts 2 framework.</p>

 <p>The <a href="http://struts.apache.org/mail">Struts 2 user mailing list</a> is an excellent place to get help. If you are having
 a problem getting the tutorial example applications to work search the Struts 2 mailing list. If you don’t find an answer
 to your problem, post a question on the mailing list.</p>

 <h2 id="example-application">Example Application</h2>

 <p>The example application that supports this tutorial shows how to use Struts 2’s XML validation methodology.
 The information that can be edited is encapsulated in an object of class Person.</p>

 <p>To enable the user to edit his information that is stored in the Person object, we have this form:</p>

 <p><img src="attachments/att20873263_form-validation-1.png" alt="form-validation-1.png" /></p>

 <p>When the user submits the form, we want to validate his entries into the form fields.</p>

 <h2 id="validation-using-xml">Validation Using XML</h2>

 <p>To validate a user’s form field entries you can use a separate XML file that contains your validation rules.
 The XML file that contains the validation rules must be named as ActionClassName-validation.xml. In the example
 application, the XML validation file is named EditAction-validation.xml (see src/main/resources/org/apache/struts/edit/action).</p>

 <p>Struts 2 provides several different validators that you can use in the XML validation file. See <a href="../core-developers/validation">Validation</a>
 for a list of validators you can employ.</p>

 <p>In the above form, we want to ensure the user enters a first name. To have the Struts 2 framework enforce that rule
 we can use the Struts 2 <a href="../core-developers/requiredstring-validator">requiredstring validator</a>. This validator checks
 that the user has entered a string value in the form field.</p>

 <h2 id="xml-validator-format">XML Validator Format</h2>

 <p>In the XML validation file (for this example that is EditAction-validation.xml), is this XML:</p>

 <p><strong>XML Validator Required String</strong></p>

 <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="cp">&lt;!DOCTYPE validators PUBLIC "-//Apache Struts//XWork Validator 1.0.3//EN" "http://struts.apache.org/dtds/xwork-validator-1.0.3.dtd"&gt;</span>

 <span class="nt">&lt;validators&gt;</span>
     <span class="nt">&lt;validator</span> <span class="na">type=</span><span class="s">"requiredstring"</span><span class="nt">&gt;</span>
         <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">&gt;</span>personBean.firstName<span class="nt">&lt;/param&gt;</span>
         <span class="nt">&lt;message&gt;</span>First name is required.<span class="nt">&lt;/message&gt;</span>
     <span class="nt">&lt;/validator&gt;</span>
 <span class="nt">&lt;/validators&gt;</span>
 </code></pre></div></div>

 <p>Within the validators node you can have 1 or more validator nodes. The type attribute specifies which validator you
 want the Struts 2 framework to use (see <a href="../core-developers/validation">Validation</a> ). The param name=”fieldname” node
 is used to tell the framework which form field entry to apply the rule to. See edit.jsp for the form fields and their
 name value (review <a href="form-tags">Struts 2 Form Tags</a> if you’re not familiar with how to use Struts 2 form tags). T
 he message node is used to tell the framework what message to display if the validation fails.</p>

 <p>| There are alternate ways to write the XML that goes in the validation XML file. See <a href="../core-developers/validation">Validation</a>
 in the Struts 2 documentation for a full discussion.</p>

 <p>For example if the user doesn’t enter a value in the first name form field and clicks on the Save Changes button, h
 e will see the following.</p>

 <p><img src="attachments/att20873264_form-validation-2.png" alt="form-validation-2.png" /></p>

 <h2 id="validating-an-email-address">Validating An Email Address</h2>

 <p>You can use the Struts 2 <a href="../core-developers/email-validator">email validator</a> to validate the user’s input in the email
 field. Here is the validator node that is in the <code class="language-plaintext highlighter-rouge">EditAction-validation.xml</code> file.</p>

 <p><strong>Email Validator</strong></p>

 <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;validator</span> <span class="na">type=</span><span class="s">"requiredstring"</span><span class="nt">&gt;</span>
     <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">&gt;</span>personBean.email<span class="nt">&lt;/param&gt;</span>
     <span class="nt">&lt;message&gt;</span>Email address is required.<span class="nt">&lt;/message&gt;</span>
 <span class="nt">&lt;/validator&gt;</span>
 <span class="nt">&lt;validator</span> <span class="na">type=</span><span class="s">"email"</span><span class="nt">&gt;</span>
     <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">&gt;</span>personBean.email<span class="nt">&lt;/param&gt;</span>
     <span class="nt">&lt;message&gt;</span>Email address not valid.<span class="nt">&lt;/message&gt;</span>
 <span class="nt">&lt;/validator&gt;</span>
 </code></pre></div></div>

 <p>Note that in the example, we are requiring the user to enter an email address and then validating the email address the user entered.</p>

 <h2 id="validating-a-users-input-using-a-regular-expression">Validating A User’s Input Using A Regular Expression</h2>

 <p>The Struts 2 framework provides a powerful way to validate a user’s form field input by using the <a href="../core-developers/regex-validator">regex validator</a>.
 In the example application, we want to ensure the user enters the phone number in the format 999-999-9999. We can use
 a regular expression and the <a href="../core-developers/regex-validator">regex validator</a> to enforce this rule.</p>

 <p><strong>REGEX Validator</strong></p>

 <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;validator</span> <span class="na">type=</span><span class="s">"requiredstring"</span><span class="nt">&gt;</span>
     <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">&gt;</span>personBean.phoneNumber<span class="nt">&lt;/param&gt;</span>
     <span class="nt">&lt;message&gt;</span>Phone number is required.<span class="nt">&lt;/message&gt;</span>
 <span class="nt">&lt;/validator&gt;</span>
 <span class="nt">&lt;validator</span> <span class="na">type=</span><span class="s">"regex"</span><span class="nt">&gt;</span>
     <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">&gt;</span>personBean.phoneNumber<span class="nt">&lt;/param&gt;</span>
     <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"regex"</span><span class="nt">&gt;</span><span class="cp">&lt;![CDATA[\d{3}-\d{3}-\d{4}]]&gt;</span><span class="nt">&lt;/param&gt;</span>
     <span class="nt">&lt;message&gt;</span>Phone number must be entered as 999-999-9999.<span class="nt">&lt;/message&gt;</span>
 <span class="nt">&lt;/validator&gt;</span>
 </code></pre></div></div>

 <p>The <code class="language-plaintext highlighter-rouge">param name="regex"</code> node is used to specify the regular expression that will be applied to the user’s input.
 Note how the regular expression is contained within a CDATA section.</p>

 <h2 id="validating-a-users-input-using-an-ognl-expression">Validating A User’s Input Using An OGNL Expression</h2>

 <p>In the example application, we want to ensure the user checks at least one of the car model check boxes. To enforce
 this rule we can use the <a href="../core-developers/fieldexpression-validator">fieldexpression validator</a>.
 Here’s the XML for that validator node.</p>

 <p><strong>FieldExpression Validator</strong></p>

 <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;validator</span> <span class="na">type=</span><span class="s">"fieldexpression"</span><span class="nt">&gt;</span>
     <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">&gt;</span>personBean.carModels<span class="nt">&lt;/param&gt;</span>
     <span class="nt">&lt;param</span> <span class="na">name=</span><span class="s">"expression"</span><span class="nt">&gt;</span><span class="cp">&lt;![CDATA[personBean.carModels.length &gt; 0]]&gt;</span><span class="nt">&lt;/param&gt;</span>
     <span class="nt">&lt;message&gt;</span>You must select at least one car model.<span class="nt">&lt;/message&gt;</span>
 <span class="nt">&lt;/validator&gt;</span>
 </code></pre></div></div>

 <p>The param name=”expression” node contains an OGNL expression that evaluates to true or false. We haven’t previously
 discussed OGNL, which stands for Object-Graph Navigation Language (see <a href="https://github.com/jkuhnert/ognl">https://github.com/jkuhnert/ognl</a>
 and <a href="../tag-developers/ognl">OGNL</a> ). OGNL expressions can be evaluated by the Struts 2 framework as Java statements.</p>

 <p>In the above XML the value of the param name=”expression” node, personBean.carModels.length &gt; 0, will be evaluated
 by the framework as a Java statement. The part personBean.carModels tells the framework to call the getCarModels
 method of class Person. That method returns an Array. Since class Array has a length attribute, the framework will get
 the value of the length attribute of the Array returned by the getCarModels method.</p>

 <p>If the user did not check any of the check boxes, the Array returned by the getCarModels method will have a length
 value of 0. Since the complete OGNL expression will only evaluate to true if the length value is greater than 0,
 the validation fails. The user will see this.</p>

 <p><img src="attachments/att20873265_form-validation-3.png" alt="form-validation-3.png" /></p>

 <p>The fieldexpression validator is useful when doing conditional validation of a user’s input. If the OGNL expression
 doesn’t evaluate to true then the user’s input won’t be allowed.</p>

 <h2 id="summary">Summary</h2>

 <p>The Struts 2 framework provides easy-to-use validation methodologies. You can add a validate method to the Action class
 or have a separate XML file with validation rules or you can use a combination of both methodologies.</p>

 <table>
   <tbody>
     <tr>
       <td>Return to <a href="form-tags">Form tags</a></td>
       <td>or</td>
       <td>onward to <a href="control-tags">Control tags</a></td>
     </tr>
   </tbody>
 </table>

   </section>
 </article>


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	<article class="container">
	<section class="col-md-12">
	<a class="edit-on-gh" href="https://github.com/apache/struts-site/edit/master/source/getting-started/form-validation-using-xml.md" title="Edit this page on GitHub">Edit on GitHub</a>

	<a href="index.html" title="back to Getting started"><< back to Getting started</a>

	<h1 class="no_toc" id="form-validation-using-xml">Form Validation Using XML</h1>

	<ul id="markdown-toc">
	<li><a href="#introduction" id="markdown-toc-introduction">Introduction</a></li>
	<li><a href="#example-application" id="markdown-toc-example-application">Example Application</a></li>
	<li><a href="#validation-using-xml" id="markdown-toc-validation-using-xml">Validation Using XML</a></li>
	<li><a href="#xml-validator-format" id="markdown-toc-xml-validator-format">XML Validator Format</a></li>
	<li><a href="#validating-an-email-address" id="markdown-toc-validating-an-email-address">Validating An Email Address</a></li>
	<li><a href="#validating-a-users-input-using-a-regular-expression" id="markdown-toc-validating-a-users-input-using-a-regular-expression">Validating A User’s Input Using A Regular Expression</a></li>
	<li><a href="#validating-a-users-input-using-an-ognl-expression" id="markdown-toc-validating-a-users-input-using-an-ognl-expression">Validating A User’s Input Using An OGNL Expression</a></li>
	<li><a href="#summary" id="markdown-toc-summary">Summary</a></li>
	</ul>

	<p>The example code for this tutorial, <strong>form-xml-validation</strong>, is available for checkout at <a href="https://github.com/apache/struts-examples">struts-examples</a></p>

	<h2 id="introduction">Introduction</h2>

	<p>In this tutorial we’ll cover how to validate a user’s input in form fields using Struts 2’s XML validation methodology.
	In the <a href="form-validation">Form Validation</a> tutorial we discussed validating a user’s input using the validate method
	in the Action class. Using a separate XML validation file gives you the ability to use validators built-in
	to the Struts 2 framework.</p>

	<p>The <a href="http://struts.apache.org/mail">Struts 2 user mailing list</a> is an excellent place to get help. If you are having
	a problem getting the tutorial example applications to work search the Struts 2 mailing list. If you don’t find an answer
	to your problem, post a question on the mailing list.</p>

	<h2 id="example-application">Example Application</h2>

	<p>The example application that supports this tutorial shows how to use Struts 2’s XML validation methodology.
	The information that can be edited is encapsulated in an object of class Person.</p>

	<p>To enable the user to edit his information that is stored in the Person object, we have this form:</p>

	<p><img src="attachments/att20873263_form-validation-1.png" alt="form-validation-1.png" /></p>

	<p>When the user submits the form, we want to validate his entries into the form fields.</p>

	<h2 id="validation-using-xml">Validation Using XML</h2>

	<p>To validate a user’s form field entries you can use a separate XML file that contains your validation rules.
	The XML file that contains the validation rules must be named as ActionClassName-validation.xml. In the example
	application, the XML validation file is named EditAction-validation.xml (see src/main/resources/org/apache/struts/edit/action).</p>

	<p>Struts 2 provides several different validators that you can use in the XML validation file. See <a href="../core-developers/validation">Validation</a>
	for a list of validators you can employ.</p>

	<p>In the above form, we want to ensure the user enters a first name. To have the Struts 2 framework enforce that rule
	we can use the Struts 2 <a href="../core-developers/requiredstring-validator">requiredstring validator</a>. This validator checks
	that the user has entered a string value in the form field.</p>

	<h2 id="xml-validator-format">XML Validator Format</h2>

	<p>In the XML validation file (for this example that is EditAction-validation.xml), is this XML:</p>

	<p><strong>XML Validator Required String</strong></p>

	<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="cp"><!DOCTYPE validators PUBLIC "-//Apache Struts//XWork Validator 1.0.3//EN" "http://struts.apache.org/dtds/xwork-validator-1.0.3.dtd"></span>

	<span class="nt"><validators></span>
	<span class="nt"><validator</span> <span class="na">type=</span><span class="s">"requiredstring"</span><span class="nt">></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">></span>personBean.firstName<span class="nt"></param></span>
	<span class="nt"><message></span>First name is required.<span class="nt"></message></span>
	<span class="nt"></validator></span>
	<span class="nt"></validators></span>
	</code></pre></div></div>

	<p>Within the validators node you can have 1 or more validator nodes. The type attribute specifies which validator you
	want the Struts 2 framework to use (see <a href="../core-developers/validation">Validation</a> ). The param name=”fieldname” node
	is used to tell the framework which form field entry to apply the rule to. See edit.jsp for the form fields and their
	name value (review <a href="form-tags">Struts 2 Form Tags</a> if you’re not familiar with how to use Struts 2 form tags). T
	he message node is used to tell the framework what message to display if the validation fails.</p>

	<p>\| There are alternate ways to write the XML that goes in the validation XML file. See <a href="../core-developers/validation">Validation</a>
	in the Struts 2 documentation for a full discussion.</p>

	<p>For example if the user doesn’t enter a value in the first name form field and clicks on the Save Changes button, h
	e will see the following.</p>

	<p><img src="attachments/att20873264_form-validation-2.png" alt="form-validation-2.png" /></p>

	<h2 id="validating-an-email-address">Validating An Email Address</h2>

	<p>You can use the Struts 2 <a href="../core-developers/email-validator">email validator</a> to validate the user’s input in the email
	field. Here is the validator node that is in the <code class="language-plaintext highlighter-rouge">EditAction-validation.xml</code> file.</p>

	<p><strong>Email Validator</strong></p>

	<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><validator</span> <span class="na">type=</span><span class="s">"requiredstring"</span><span class="nt">></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">></span>personBean.email<span class="nt"></param></span>
	<span class="nt"><message></span>Email address is required.<span class="nt"></message></span>
	<span class="nt"></validator></span>
	<span class="nt"><validator</span> <span class="na">type=</span><span class="s">"email"</span><span class="nt">></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">></span>personBean.email<span class="nt"></param></span>
	<span class="nt"><message></span>Email address not valid.<span class="nt"></message></span>
	<span class="nt"></validator></span>
	</code></pre></div></div>

	<p>Note that in the example, we are requiring the user to enter an email address and then validating the email address the user entered.</p>

	<h2 id="validating-a-users-input-using-a-regular-expression">Validating A User’s Input Using A Regular Expression</h2>

	<p>The Struts 2 framework provides a powerful way to validate a user’s form field input by using the <a href="../core-developers/regex-validator">regex validator</a>.
	In the example application, we want to ensure the user enters the phone number in the format 999-999-9999. We can use
	a regular expression and the <a href="../core-developers/regex-validator">regex validator</a> to enforce this rule.</p>

	<p><strong>REGEX Validator</strong></p>

	<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><validator</span> <span class="na">type=</span><span class="s">"requiredstring"</span><span class="nt">></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">></span>personBean.phoneNumber<span class="nt"></param></span>
	<span class="nt"><message></span>Phone number is required.<span class="nt"></message></span>
	<span class="nt"></validator></span>
	<span class="nt"><validator</span> <span class="na">type=</span><span class="s">"regex"</span><span class="nt">></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">></span>personBean.phoneNumber<span class="nt"></param></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"regex"</span><span class="nt">></span><span class="cp"><![CDATA[\d{3}-\d{3}-\d{4}]]></span><span class="nt"></param></span>
	<span class="nt"><message></span>Phone number must be entered as 999-999-9999.<span class="nt"></message></span>
	<span class="nt"></validator></span>
	</code></pre></div></div>

	<p>The <code class="language-plaintext highlighter-rouge">param name="regex"</code> node is used to specify the regular expression that will be applied to the user’s input.
	Note how the regular expression is contained within a CDATA section.</p>

	<h2 id="validating-a-users-input-using-an-ognl-expression">Validating A User’s Input Using An OGNL Expression</h2>

	<p>In the example application, we want to ensure the user checks at least one of the car model check boxes. To enforce
	this rule we can use the <a href="../core-developers/fieldexpression-validator">fieldexpression validator</a>.
	Here’s the XML for that validator node.</p>

	<p><strong>FieldExpression Validator</strong></p>

	<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><validator</span> <span class="na">type=</span><span class="s">"fieldexpression"</span><span class="nt">></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"fieldname"</span><span class="nt">></span>personBean.carModels<span class="nt"></param></span>
	<span class="nt"><param</span> <span class="na">name=</span><span class="s">"expression"</span><span class="nt">></span><span class="cp"><![CDATA[personBean.carModels.length > 0]]></span><span class="nt"></param></span>
	<span class="nt"><message></span>You must select at least one car model.<span class="nt"></message></span>
	<span class="nt"></validator></span>
	</code></pre></div></div>

	<p>The param name=”expression” node contains an OGNL expression that evaluates to true or false. We haven’t previously
	discussed OGNL, which stands for Object-Graph Navigation Language (see <a href="https://github.com/jkuhnert/ognl">https://github.com/jkuhnert/ognl</a>
	and <a href="../tag-developers/ognl">OGNL</a> ). OGNL expressions can be evaluated by the Struts 2 framework as Java statements.</p>

	<p>In the above XML the value of the param name=”expression” node, personBean.carModels.length > 0, will be evaluated
	by the framework as a Java statement. The part personBean.carModels tells the framework to call the getCarModels
	method of class Person. That method returns an Array. Since class Array has a length attribute, the framework will get
	the value of the length attribute of the Array returned by the getCarModels method.</p>

	<p>If the user did not check any of the check boxes, the Array returned by the getCarModels method will have a length
	value of 0. Since the complete OGNL expression will only evaluate to true if the length value is greater than 0,
	the validation fails. The user will see this.</p>

	<p><img src="attachments/att20873265_form-validation-3.png" alt="form-validation-3.png" /></p>

	<p>The fieldexpression validator is useful when doing conditional validation of a user’s input. If the OGNL expression
	doesn’t evaluate to true then the user’s input won’t be allowed.</p>

	<h2 id="summary">Summary</h2>

	<p>The Struts 2 framework provides easy-to-use validation methodologies. You can add a validate method to the Action class
	or have a separate XML file with validation rules or you can use a combination of both methodologies.</p>

	<table>
	<tbody>
	<tr>
	<td>Return to <a href="form-tags">Form tags</a></td>
	<td>or</td>
	<td>onward to <a href="control-tags">Control tags</a></td>
	</tr>
	</tbody>
	</table>

	</section>
	</article>


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