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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/tag-developers/freemarker-tags.md" title="Edit this page on GitHub">Edit on GitHub</a> |
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| <a href="index" title="back to Tag Developers Guide"><< back to Tag Developers Guide</a> |
| |
| <h1 class="no_toc" id="freemarker-tags">FreeMarker Tags</h1> |
| |
| <ul id="markdown-toc"> |
| <li><a href="#attributes-and-parameters" id="markdown-toc-attributes-and-parameters">Attributes and Parameters</a> <ul> |
| <li><a href="#using-inline-attributes-with-templates" id="markdown-toc-using-inline-attributes-with-templates">Using inline attributes with templates</a></li> |
| </ul> |
| </li> |
| <li><a href="#attribute-types" id="markdown-toc-attribute-types">Attribute Types</a></li> |
| <li><a href="#jsp-tag-support" id="markdown-toc-jsp-tag-support">JSP Tag Support</a></li> |
| </ul> |
| |
| <p>FreeMarker tags are extensions of the generic <a href="struts-tags">Struts Tags</a> provided by the framework. You can jump |
| right in just by knowing the generic structure in which the tags can be accessed:</p> |
| |
| <pre><code class="language-ftl"><@s.tag> ...</@s.tag> |
| </code></pre> |
| |
| <p>, where <code class="highlighter-rouge">tag</code> is any of the <a href="tag-reference">tags</a> supported by the framework.</p> |
| |
| <p>For example, in JSP you might create a form using Struts tags.</p> |
| |
| <p><strong>JSP Form</strong></p> |
| |
| <pre><code class="language-jsp"><s:form action="updatePerson"> |
| <s:textfield label="First name" name="firstName"/> |
| <s:submit value="Update"/> |
| </s:form> |
| </code></pre> |
| |
| <p>In FreeMarker the same form can also be built using Struts tags.</p> |
| |
| <p><strong>FTL Form</strong></p> |
| |
| <pre><code class="language-ftl"><@s.form action="updatePerson"> |
| <@s.textfield label="First name" name="firstName"/> |
| <@s.submit value="Update"/> |
| </@s.form> |
| </code></pre> |
| |
| <p><strong>But, wait there’s more!</strong></p> |
| |
| <p>Aside from doing everything that the JSP tags do, the FTL tags boast additional features that you can use to make your |
| pages even easier to code. You can even invoke third-party JSP taglibs as if there were native FTL tags.</p> |
| |
| <h2 id="attributes-and-parameters">Attributes and Parameters</h2> |
| |
| <p>Unlike older versions of JSP (in which the <a href="jsp-tags">JSP Tags</a> are based), FreeMarker allows for <em>dynamic attributes</em>, |
| much like JSP 2.0. You can supply attributes to the tags that the tag doesn’t explicitedly support. Those attributes |
| that cannot be applied directly to the tag object will be set to the tag’s general-purpose <code class="highlighter-rouge">parameters</code> Map.</p> |
| |
| <p>Suppose we wanted to build an URL in a JSP. The URL needs to take an arbitary parameter to the query string, |
| that (being arbitary) isn’t specified on the URL tag. In a JSP, we’d have to use the <code class="highlighter-rouge">url</code> and <code class="highlighter-rouge">param</code> tags together.</p> |
| |
| <p><strong>Creating a URL with a query string (JSP)</strong></p> |
| |
| <pre><code class="language-jsp"><s:url value="somePage"> |
| <s:param name="personId" value="%{personId}"/> |
| </s:url> |
| </code></pre> |
| |
| <p>In FreeMarker, we can pass the arbitrary parameter directly and create the URL in one simple statement.</p> |
| |
| <p><strong>Creating a URL with a query string (FTL)</strong></p> |
| |
| <pre><code class="language-ftl"><@s.url value="somePage" personId="%{personId}"/> |
| </code></pre> |
| |
| <h3 id="using-inline-attributes-with-templates">Using inline attributes with templates</h3> |
| |
| <p>Suppose you created a “three column” theme to replace the typical two column theme (xhtml). You might want an additional |
| parameter to display in the third column called “description”. Using FreeMarker, you can just pop the description |
| attribute into the textfield tag, no fuss, no muss.</p> |
| |
| <p><strong>Passing an attribute to the template</strong></p> |
| |
| <pre><code class="language-ftl"><@s.form action="updatePerson"> |
| <@s.textfield label="First name" name="firstName" description="..."/> |
| <@s.submit value="Update"/> |
| </@s.form> |
| </code></pre> |
| |
| <p>In the new template, the description is referenced via the parameters Map: <code class="highlighter-rouge">${parameters.description}</code>.</p> |
| |
| <blockquote> |
| <p>For simple cases, inline attributes are much easier to use than the param} tag. But, the <code class="highlighter-rouge">param</code> tag is more flexible |
| than inline attributes for advanced use cases. For example, <code class="highlighter-rouge">param</code> can take the entire body of the tag and apply |
| that as the <code class="highlighter-rouge">value</code> attribute.</p> |
| </blockquote> |
| |
| <h2 id="attribute-types">Attribute Types</h2> |
| |
| <p>Remember that all tag attributes must first be set as Strings - they are then later evaluated (using <a href="ognl">OGNL</a>) |
| to a different type, such as List, int, or boolean. This generally works just fine, but it can be limiting when using |
| FreeMarker which provides more advanced ways to apply attributes. Suppose the following example:</p> |
| |
| <pre><code class="language-ftl"><@s.select label="Foo label - %{foo}" name="%{name}" list="%{1, 2, 3}"/> |
| </code></pre> |
| |
| <p>What will happen here is that each attribute will be evaluated to a String as best it can. This may involve calling the |
| <code class="highlighter-rouge">toString</code> method on the internal FreeMarker objects. In this case, all objects will end up being exactly what you would |
| expect. Then, when the tag runs, the <code class="highlighter-rouge">list</code> attribute will be converted from a String to a List using <a href="ognl">OGNL</a>’s |
| advanced collection support.</p> |
| |
| <p>But suppose you wish to use FreeMarker’s list or hash support instead? You can do this:</p> |
| |
| <pre><code class="language-ftl"><@s.select label="Foo label - %{foo}" name="%{name}" list=[1, 2, 3]/> |
| </code></pre> |
| |
| <p>Notice that the list attribute no longer has quotes around it. Now it will come in to the tag as an object that can’t |
| easily be converted to a String. Normally, the tag would just call <code class="highlighter-rouge">toString</code>, which would return <code class="highlighter-rouge">[1, 2, 3]</code> and be |
| unable to be converted back to a List by OGNL. Rather than go through all this back and forth, the frameworks’s FreeMarker |
| tag support will recognize collections and not pass them through the normal tag attribute. Instead, the framework will |
| set them directly in the <code class="highlighter-rouge">parameters</code> Map, ready to be consumed by the template.</p> |
| |
| <p>In the end, everything tends to do what you would expect, but it can help to understand the difference of when OGNL is |
| being used and when it isn’t, and how attribute types get converted.</p> |
| |
| <h2 id="jsp-tag-support">JSP Tag Support</h2> |
| |
| <p>While the framework provides native FreeMarker Tags, you might wish to use other third-party tags that are only available |
| for JSP. Fortunately, FreeMarker has the ability to run JSP tags. To do so, you must include the JspSupportServlet in |
| the application’s <code class="highlighter-rouge">web.xml</code>, as this allows the FreeMarker integration to get access to the required objects needed |
| to emulate a JSP taglib container.</p> |
| |
| <p><strong>Adding JspSupportSerlvet to web.xml</strong></p> |
| |
| <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><servlet></span> |
| <span class="nt"><servlet-name></span>JspSupportServlet<span class="nt"></servlet-name></span> |
| <span class="nt"><servlet-class></span>org.apache.struts2.views.JspSupportServlet<span class="nt"></servlet-class></span> |
| <span class="nt"><load-on-startup></span>1<span class="nt"></load-on-startup></span> |
| <span class="nt"></servlet></span> |
| </code></pre></div></div> |
| |
| <p>Once you’ve done that, you can simply add something like this in your templates:</p> |
| |
| <pre><code class="language-ftl"><#assign cewolf=JspTaglibs["/WEB-INF/cewolf.tld"] /> |
| ... |
| <@cewold.xxx ... /> |
| </code></pre> |
| |
| </section> |
| </article> |
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