In the Hello World lesson, we presented a page with a simple Welcome message. In the Using Tags lesson, we create a Welcome page with links to other actions in the application.

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 while providing added value. Other tags create non-standard, but useful controls.

One use of the Struts Tags is to create links to other web resources, especially to other resources in the local application.

While HTML provides a simple a tag for creating hyperlinks, the HTML tag often requires us to include redundant information. Also the HTML tag cannot easily access dynamic data provided by the framework.

Linking

A very common use case 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.

The 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>
</body>
</html>

Another common use case is using a link to change locales. On the HelloWorld page, let's add links to change the user's locale and to display a message from the application resources.

HelloWorld.jsp
<body>
<h2><s:property value="message"/></h2>

<h3>Languages</h3>
<ul>
    <li>
        <s:url var="url" action="Welcome">
            <s:param name="request_locale">en</s:param>
        </s:url>
        <s:a href="%{url}">English</s:a>
    </li>
    <li>
        <s:url var="url" action="Welcome">
            <s:param name="request_locale">es</s:param>
        </s:url>
        <s:a href="%{url}">Espanol</s:a>
    </li>
</ul>
</body>

The var attribute (used in the <s:url...> tags) was introduced in Struts 2.1; use the id attribute in its place with Struts 2.0.

How the Code Works

"%{url}" will be evaluated to the url defined with the s:url tag. On the Welcome and HelloWorld pages, we use two different Struts tags to create links. We create

  • Resource links
  • Direct links, and
  • Links with parameters.

Let's look at each in turn.

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 containing the link around without worrying about resolving relative references.

The url tag will also inject the web application context name.

In the "Commands" section, we use the url tag again, to link to a Struts 2 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 information across 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 across requests.

Links with parameters

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

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

This 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. This request_locale parameter will be picked up by the I18n Interceptor, and change your Locale accordingly.

(tick) Any number of parameters can be added to the URI by adding more param tags.

Wildcard Mappings

Since the Welcome page is nothing but links, we don't need an Action class. We'll still use a mapping, however, so we can use an action URI. If we link only to actions, and never to pages, then it's easy to add an Action class later. 

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

As we create the application, we will often want to go directly to a page. To make prototyping easy, we can change the Welcome entry to a wilcard mapping.

The Code

struts.xml
<action name="*" >
  <result>/{1}.jsp</result>
</action>

How the Code Works

If no other mapping matches, the framework will

  • match "Welcome" to the asterisk, and
  • substitute "Welcome" for any "{1}" tokens in the mapping.

Likewise, if there is a link to a "Login" action, and nothing else matches, then the "/Login.jsp" page is returned instead.

(tick) Wildcard mappings let you create your own conventions, so that you can avoid redundant configuration. The first mapping that matches a request wins. (So put a mapping like <action name="*" > last!)

If you are coding along, you can replace the Welcome action in your struts.xml with the Wildcard version.

Data Entry Forms

Most applications will use several data entry forms. The Struts Tags make creating input forms easy.

The Code

Logon.jsp
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
  <title>Login</title>
</head>
<body>
<s:form action="Logon"> 
  <s:textfield label="User Name" name="username"/>
  <s:password label="Password" name="password" />
  <s:submit/>
</s:form>
</body>
</html>

How The Code Works

  • The JSP engine reads the taglib reference at the top of the page and loads the Struts Tags for use with this page under the prefix "s".
  • The Struts Tags – textfield, password, and submit – each emit the appropriate label and control type.

What to Remember

The hardest part of writing a web application can be coding the pages. The framework makes coding pages easier by providing a set of custom tags. The Struts Tags can access dynamic data provided by the framework. Tags reduce the amount of markup needed to create a page.

(lightbulb) For more about Struts Tags, see the Tag Developers Guide.
(lightbulb) For more on how to access action members, request attributes and others from pages, see OGNL.

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19 Comments

  1. Jan Normann Nielsen

    Spelling error: Replace "a Action" with "an Action" in the section "Wildcard Mappings". Replace "strut.xml" with "struts.xml" in the section. "How the Code Works".

    1. Dave Newton

      This appears to have been fixed; thanks for the feedback.

  2. Hernan Soulages

    Another spelling error: Replay "A very common use cases in web" with "A very common use case in web"

    1. Dave Newton

      Fixed; thanks for the feedback.

  3. Anton Pussep

    The actions in struts.xml should forward to the JSPs directly, "/Welcome.jsp" instead of "/tutorial/Welcome.jsp" and "

    Unknown macro: {1}

    .jsp" instead of "/tutorial/

    .jsp". Otherwise very nice tutorial, too bad I cannot modify it myself.

    1. Dave Newton

      Fixed; thanks for the feedback.

  4. Zahi Aizer

    There are few coding errors that prevent running the examples.
    1) HelloWorld.jsp - The value of "action" attributes in the "s:url" element should be changed from "HelloWorld" to "Welcome" (as presented in the "Links with parameters" example).

    2) Based on Maven project structure all jsp pages are located in "jsp" folder. Hence, the wildcard action definition should be changed from:
    "/tutorial/

    Unknown macro: {1}

    .jsp" to "/jsp/

    .jsp".

    3) In "Wildcard Mappings" section the String "so that we can use use an action URI" should be replaced with "so that we can use an action URI".

    1. Dave Newton

      Fixed; thanks for the feedback (although I changed it from Welcome to HelloWorld for consistency).

  5. David Durham

    In Struts 2.1, the 'id' attribute of <s:url .. /> is deprecated in favor or 'var'.

    1. Dave Newton

      Updated; thanks.

      1. Mitchell Gould

        I think you could state that for Struts Prior to 2.1 it should be
        <s:url id="url" action="Welcome">

        and for 2.1

        <s:url var="url" action="Welcome">

        Thanks

        1. Devin Barnhart

          I agree, I spent about an hour trying to figure this out. In defense of the editors I'll add that I should have read the comments. But my dog - I mean my NoScript plug-in ate them up (lame excuse (smile).

      2. Jim Kiley

        I could be missing something but it doesn't appear to be updated – there are still plenty of references to 'var' up there instead of 'id'. This threw a coworker of mine off before he leaned over the cube wall to ask.

        1. Philip Luppens

          Hmm, this page seems to be using the new var attribute alright - what pages are you referring to ?

  6. David M. Sledge

    Any possibility of seeing these .jsp examples in xml syntax?

  7. Anonymous

    Where it is "Any number of parameters can be added to the URI by adding more param etags." it should be "Any number of parameters can be added to the URI by adding more param tags."

    1. Dave Newton

      Fixed; thanks for the feedback.

  8. newt gatt

    what is the structure of this example,
    the directories, etc

    tried different places for the jsp's ,

    if they want to give a tutorial, give a tutorial,
    please dont make it into a guessing game
    and try it out before you put it on the internet for the apache org

    Thanks

    1. Philip Luppens

      In this example, the .jsp files are placed under the root of the webapp (the path you enter is always relative to the webapp root, hence /foo.jsp will translate to /webapp/foo.jsp). Personally, I always put them under /WEB-INF/jsp/, so that the jsp files by themselves are not directly readable. In that case, the result would look something like this: <result>/WEB-INF/jsp/foo.jsp</result>.

      If you encounter these problems, please ask help on the struts user mailing list.