Using Tags

Web applications differ from conventional websites in that web applications can create a dynamic response. To make it easier to reference dynamic data from a page, the framework offers a set of tags. Some of the tags mimic standard HTML tag, but provided added value. Other tags create non-standard, but useful controls.

A very common use cases in web applications is linking to other pages. Now that we know Struts is up and running, let's add a Welcome page with links to other actions.

Page Code

Welcome.jsp

<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
    <title>Welcome</title>
    <link href="<s:url value="/css/tutorial.css"/>" rel="stylesheet"
          type="text/css"/>
</head>
<body>
<h3>Commands</h3>
<ul>
    <li><a href="<s:url action="Register"/>">Register</a></li>
    <li><a href="<s:url action="Logon"/>">Sign On</a></li>
</ul>

<h3>Languages</h3>
<ul>
    <li>
        <s:url id="url" action="Welcome">
            <s:param name="request_locale">en</s:param>
        </s:url>
        <s:a href="%{url}">English</s:a>
    </li>
    <li>
        <s:url id="url" action="Welcome">
            <s:param name="request_locale">ja</s:param>
        </s:url>
        <s:a href="%{url}">Japanese</s:a>
    </li>
</ul>

</body>
</html>

On the Welcome page, we use two different Struts tags to create links.

Resource links

First, in the head element, we use the url tag to inject a page reference into the HTML link tag.

<link href="<s:url value="/css/tutorial.css"/>" 
  rel="stylesheet" type="text/css"/>

Note that the reference is absolute. We can move the page around without worrying about resolving relative references.

Direct links

In the "Commands" section, we use the url link again, to inject a reference to an Action.

<li><a href="<s:url action="Register"/>">Register</a></li>

When the link is rendered, the tag will automatically append the appropriate extension, so that we do not need to embed that fact all over the application.

The tag will also URL-encode the link with the Java session ID, if needed, so that the Java session can be retained accross requests.

Links with parameters

Finally, in the Languages section, we use the url tag along with the param and a tags to create a link with request parameters.

<s:url id="url" action="Welcome">
  <s:param name="request_locale">en</s:param>
</s:url>
<s:a href="%{url}">English</s:a>

The param tag will add the parameter "?request_locale=en" to the Welcome Action URL, and store it under the name "url". The a tag then injects the "url" reference into the hyperlink.

Any number of parameters can be added to the URI by adding more param etags.

The framework provides an array of tags, ranging from the mundane to the insane. See the Tag Developers Guide for details.

Mapping Code

Since the Welcome page is simple, we don't need an Action. But, we should still add a mapping, so that we can use use an action URI. If we link only to actions, and never to pages, then it's easy to add a Action class later.

<action name="Welcome" >
<result>/tutorial/Welcome.jsp</result>
</action>

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