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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.md" title="Edit this page on GitHub">Edit on GitHub</a> |
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| <a href="index.html" title="back to Getting started"><< back to Getting started</a> |
| |
| <h1 class="no_toc" id="form-validation">Form Validation</h1> |
| |
| <ul id="markdown-toc"> |
| <li><a href="#introduction" id="markdown-toc-introduction">Introduction</a></li> |
| <li><a href="#add-validate-method" id="markdown-toc-add-validate-method">Add validate Method</a></li> |
| <li><a href="#handle-input-being-returned" id="markdown-toc-handle-input-being-returned">Handle Input Being Returned</a></li> |
| <li><a href="#error-messages" id="markdown-toc-error-messages">Error Messages</a></li> |
| <li><a href="#styling-the-error-messages" id="markdown-toc-styling-the-error-messages">Styling The Error Messages</a></li> |
| <li><a href="#summary" id="markdown-toc-summary">Summary</a></li> |
| <li><a href="#up-next" id="markdown-toc-up-next">Up Next</a></li> |
| </ul> |
| |
| <p>This tutorial assumes you’ve completed the <a href="processing-forms.html">Processing Forms</a> tutorial and have a working |
| <strong>form-processing</strong> project. The example code for this tutorial, <strong>form-validation</strong>, is available for checkout from |
| the Struts 2 GitHub repository <a href="https://github.com/apache/struts-examples">struts-examples</a>.</p> |
| |
| <h2 id="introduction">Introduction</h2> |
| |
| <p>In this tutorial we’ll explore using Struts 2 to validate the user’s input on a form. There are two ways you can use Struts 2 |
| to do form validation. This tutorial will cover the more basic method, where the validation is included in the Struts 2 Action class.</p> |
| |
| <p>The <a href="http://struts.apache.org/mail.html">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="add-validate-method">Add validate Method</h2> |
| |
| <p>To enable the Struts 2 Action class to validate a user’s input on a Struts 2 form, you must define a validate method |
| in your Action class. Using the example from <a href="processing-forms.html">Processing Forms</a> tutorial, let’s say that we have |
| these business rules:</p> |
| |
| <ol> |
| <li>User must provide a first name</li> |
| <li>User must provide an email address</li> |
| <li>User younger than 18 cannot register</li> |
| </ol> |
| |
| <p>If you recall from the <a href="processing-forms.html">Processing Forms</a> tutorial the user’s input into the form fields is placed |
| by Struts 2 into the Java model class <code class="highlighter-rouge">personBean</code>. So a user’s input into the <code class="highlighter-rouge">firstName</code> field would end up as the value |
| for <code class="highlighter-rouge">personBean</code>’s <code class="highlighter-rouge">firstName</code> instance field (via the <code class="highlighter-rouge">personBean.setFirstName</code> method).</p> |
| |
| <p>In the validate method we can refer to get the values of personBean’s instance fields by using the appropriate get methods. |
| Once we have the values we can employ logic to enforce our business rules.</p> |
| |
| <p>Add the following validate method to <code class="highlighter-rouge">Register.java</code> (the Action class).</p> |
| |
| <p><strong>validate method</strong></p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kt">void</span> <span class="nf">validate</span><span class="o">(){</span> |
| <span class="k">if</span> <span class="o">(</span><span class="n">personBean</span><span class="o">.</span><span class="na">getFirstName</span><span class="o">().</span><span class="na">length</span><span class="o">()</span> <span class="o">==</span> <span class="mi">0</span><span class="o">)</span> <span class="o">{</span> |
| <span class="n">addFieldError</span><span class="o">(</span><span class="s">"personBean.firstName"</span><span class="o">,</span> <span class="s">"First name is required."</span><span class="o">);</span> |
| <span class="o">}</span> |
| |
| <span class="k">if</span> <span class="o">(</span><span class="n">personBean</span><span class="o">.</span><span class="na">getEmail</span><span class="o">().</span><span class="na">length</span><span class="o">()</span> <span class="o">==</span> <span class="mi">0</span><span class="o">)</span> <span class="o">{</span> |
| <span class="n">addFieldError</span><span class="o">(</span><span class="s">"personBean.email"</span><span class="o">,</span> <span class="s">"Email is required."</span><span class="o">);</span> |
| <span class="o">}</span> |
| |
| <span class="k">if</span> <span class="o">(</span><span class="n">personBean</span><span class="o">.</span><span class="na">getAge</span><span class="o">()</span> <span class="o"><</span> <span class="mi">18</span><span class="o">)</span> <span class="o">{</span> |
| <span class="n">addFieldError</span><span class="o">(</span><span class="s">"personBean.age"</span><span class="o">,</span> <span class="s">"Age is required and must be 18 or older"</span><span class="o">);</span> |
| <span class="o">}</span> |
| <span class="o">}</span> |
| </code></pre></div></div> |
| |
| <p>When the user presses the submit button on the register form, Struts 2 will transfer the user’s input to the personBean’s |
| instance fields. Then Struts 2 will automatically execute the validate method. If any of the if statements are true, |
| Struts 2 will call its <code class="highlighter-rouge">addFieldError</code> method (which our Action class inherited by extending ActionSupport).</p> |
| |
| <p>If any errors have been added then Struts 2 will not proceed to call the execute method. Rather the Struts 2 framework |
| will return <code class="highlighter-rouge">input</code> as the result of calling the action.</p> |
| |
| <h2 id="handle-input-being-returned">Handle Input Being Returned</h2> |
| |
| <p>So what should we do if Struts 2 returns <code class="highlighter-rouge">input</code> indicating that the user’s input in the form is not valid? In most cases |
| we will want to redisplay the web page that has the form and include in the form error messages to inform the user what is wrong.</p> |
| |
| <p>To handle the return value of <code class="highlighter-rouge">input</code> we need to add the following result to our action node in <code class="highlighter-rouge">struts.xml</code>.</p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><result</span> <span class="na">name=</span><span class="s">"input"</span><span class="nt">></span>/register.jsp<span class="nt"></result></span> |
| </code></pre></div></div> |
| |
| <p>The above result node goes just after the success result node for the register action and before the closing of the action node.</p> |
| |
| <h2 id="error-messages">Error Messages</h2> |
| |
| <p>So when validation fails and Struts 2 returns input, the Struts 2 framework will redisplay the <code class="highlighter-rouge">register.jsp</code>. Since we |
| used Struts 2 form tags, automatically Struts 2 will add the error messages. These error messages are the ones we specified |
| in the <code class="highlighter-rouge">addFieldError</code> method call. The addFieldError method takes two arguments. The first is the form field name to which |
| the error applies and the second is the error message to display above that form field.</p> |
| |
| <p>So the following <code class="highlighter-rouge">addFieldError</code> method call:</p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">addFieldError</span><span class="o">(</span><span class="s">"personBean.firstName"</span><span class="o">,</span> <span class="s">"First name is required."</span><span class="o">)</span> |
| </code></pre></div></div> |
| |
| <p>will cause the message <em>First name is required</em> to be displayed above the <code class="highlighter-rouge">firstName</code> field on the form.</p> |
| |
| <p>If you have made the above changes to the <a href="processing-forms.html">Processing Forms</a> tutorial or you have downloaded |
| from <a href="https://github.com/apache/struts-examples/tree/master/form-validation">form-validation</a> |
| run the application (see the README.txt in the project root folder). Click on the Please register link. On the registration |
| form, just click the submit button and you should see:</p> |
| |
| <p><img src="attachments/att14975003_form_errors.png" alt="form_errors.png" /></p> |
| |
| <p>Struts 2 called the validate method, validation failed, the <code class="highlighter-rouge">register.jsp</code> was displayed with the error messages.</p> |
| |
| <h2 id="styling-the-error-messages">Styling The Error Messages</h2> |
| |
| <p>The Struts 2 <code class="highlighter-rouge">s:head</code> tag can be used to provide CSS that includes a style for the error message. Add <code class="highlighter-rouge"><s:head /></code> |
| to <code class="highlighter-rouge">register.jsp</code> before the closing HTML <code class="highlighter-rouge"></head></code> tag. Go through the same steps as above and you should see:</p> |
| |
| <p><img src="attachments/att14975001_form_errors_styled.png" alt="form_errors_styled.png" /></p> |
| |
| <h2 id="summary">Summary</h2> |
| |
| <p>This tutorial covered validating a user’s form input by adding a validate method to an Action class. There is another |
| more sophisticated way to validate user input using XML. If you want to learn more about using XML for validation |
| in Struts 2 see <a href="../core-developers/validation.html">Validation</a> .</p> |
| |
| <h2 id="up-next">Up Next</h2> |
| |
| <p>In our next tutorial we’ll cover how to use message resource files to separate out the text from the view page.</p> |
| |
| <table> |
| <tbody> |
| <tr> |
| <td>Return to <a href="processing-forms.html">Processing Forms</a></td> |
| <td>or</td> |
| <td>onward to <a href="message-resource-files.html">Message resource files</a></td> |
| </tr> |
| </tbody> |
| </table> |
| |
| </section> |
| </article> |
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