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# Themes

The example code for this tutorial, themes, is available for checkout at struts-examples

## Introduction

When you use a Struts tag such as `s:select` in your web page, the Struts framework generates HTML that styles the appearance and controls the layout of the select control. The style and layout is determined by which Struts theme is set for the tag. Struts comes with four built-in themes: `simple`, `xhtml`, `css_xhtml`, and `html5`. If you don’t specify a theme, then Struts will use the `xhtml` theme by default.

The Struts user mailing list is an excellent place to get help. If you are having a problem getting the tutorial example applications to work search the Struts mailing list. If you don’t find an answer to your problem, post a question on the mailing list.

For example, this Struts select tag:

Struts Select Tag

    <s:select key="personBean.sport" list="sports" />

generates this HTML markup:

HTML Created By Struts Select Tag

    <tr>
        <td class="tdLabel">
            <label for="save_personBean_sport" class="label">Favorite sport:</label>
        </td>
        <td>
            <select name="personBean.sport" id="save_personBean_sport">
                <option value="football">football</option>
                <option value="baseball">baseball</option>
                <option value="basketball" selected="selected">basketball</option>
            </select>
        </td>
    </tr>

Notice how the HTML generated uses table tags to control the layout of the label and select HTML. There is also a class, `tdLabel`, applied to the table column where the label tag is rendered. Since no theme was specified for the Struts select tag the default `xhtml` theme was used.

## Specifying The Theme Struts Should Use

The Struts tags have a theme attribute you can use to specify which Struts theme should be used when creating the HTML for that tag. The values for the theme attribute are `simple`, `xhtml`, `css_xhtml`, `html5`, and `ajax`. To learn more about these themes visit Themes and Templates Documentation. This tutorial will review the `xhtml`, `css_xhtml`, and the `simple` themes. The `html5` theme extends the simple theme with modern HTML5 output (see HTML5 Theme in the documentation. The `ajax` theme is a special theme used for ajax operations (see Ajax Theme in the documentation).

You can specify the theme on a per Struts tag basis or you can use one of the following methods to specify what theme Struts should use:

1. The `theme` attribute on the specific tag
2. The `theme` attribute on a tag’s surrounding form tag
3. The page-scoped attribute named `theme`
4. The request-scoped attribute named `theme`
5. The session-scoped attribute named `theme`
6. The application-scoped attribute named `theme`
7. The `struts.ui.theme` constant in `struts.xml` (defaults to `xhtml`)

Consult Selecting Themes for how to set the theme using the above approaches.

In the example application, examine `edit.jsp`. The theme attribute of the form tag is set to `xhtml`. Run the application (see the readme.txt file) and view the source for edit.jsp after it is rendered in your browser. You should see the form HTML tags layout controlled by table tags.

Change the theme to `simple` for the form’s theme attribute and redeploy the application. Examine the source for `edit.jsp` after it is rendered in the browser. You should see that there are no table tags controlling the layout and also there are no label tags for the text fields.

Change the theme to `css_xhtml` for the form’s theme attribute and redeploy the application. Examine the source for `edit.jsp` after it is rendered in the browser. The layout of the form tags is now controlled by div tags and the label tags are back.

## Specifying The CSS Used By The Struts Tag

Change the theme attribute for the form tag back to xhtml. Notice when you view the source of edit.jsp after it is rendered in the browser that there is a class named tdLabel applied to the table column that contains the label. This CSS class controls the position of the label in the table column. The tdLabel style is defined in `/themes/struts/xhtml/styles.css`. The link to this style sheet was included in edit.jsp’s head section when you add the `s:head` tag to `edit.jsp`.

Load this style sheet in your browser (in the example application the link is http://localhost:8080/themes/struts/xhtml/styles.css if your Servlet container is running on localhost, port 8080). You’ll see the following:

styles.css

    .label {font-style:italic; }
    .errorLabel {font-style:italic; color:red; }
    .errorMessage {font-weight:bold; color:red; }
    .checkboxLabel {}
    .checkboxErrorLabel {color:red; }
    .required {color:red;}
    .tdLabel {text-align:right; vertical-align:top; }

So the .label selector renders the label tag’s text in italic. The .tdLabel tag specifies that the text should align to the right and top of the table column.

You can override the above selectors by including the same selectors in your page’s head section. For example add the following to the head section of `edit.jsp`.

Override Label Style

    <style type="text/css">
        .label {color:blue; font-style:normal; font-weight:bold}
    </style>

Now the label tag will render the text in blue, bold, normal (not italics) style.

## Creating And Applying Your Own Themes For Struts Tags

The theme templates (simple, xhtml, css_xhtml) can be found in the Struts core jar file. If you expand (extract the files) the Struts core jar file you’ll find folders named `template.css_xhtml`, `template.simple`, and `template.xhtml`. Those folders contain the templates for the three default Struts themes. In each folder is a file for each Struts tag. For example if you expand the `template.xhtml` folder you’ll see the `select.ftl` file.

The Struts framework uses the FreeMarker template engine to generate the HTML for the Struts tags. That’s why the file extension is `.ftl`. You can learn more about FreeMarker by visiting https://freemarker.apache.org/.

Also in the `template.xhmtl` folder is the `styles.css` file. This is the `styles.css` file that your application will use if it uses the `xhtml` theme.

Let’s say we wanted to create our own theme that will change how the Struts checkboxlist tag displays the checkboxes and their labels.

In the example application I’ve extended the default XHMTL theme (see file `theme.properties` under `src/main/resources/template/KUTheme`). The `checkboxlist.ftl` theme that is part of the XHTML theme only includes a space between each label and the next checkbox (see `checkboxlist.ftl` in the `template/simple` folder in Struts core). That is why all the checkboxes are displayed across the width of the browser window. For my custom checkboxlist theme I want to have a break tag after each label tag so that each checkbox and its label will be on their own line.

In the example application there is a folder named `src/main/resources/template/KUTheme`. In that folder is a `checkboxlist.ftl`, the contents of which I originally copied from the `checkboxlist.ftl` that is in the `templates.xhtml` folder from the Struts core jar.

I then modified the `checkboxlist.ftl` in the KUTheme folder to be:

Modified checkboxlist.ftl

    <#include "/${attributes.templateDir}/${attributes.expandTheme}/controlheader.ftl" />

    <#include "/${attributes.templateDir}/KUTheme_simple/checkboxlist.ftl" />

    <#include "/${attributes.templateDir}/${attributes.expandTheme}/controlfooter.ftl" /><#nt/>

Be sure to note the change to the second line—using KUTheme_simple in the path.

Then in the example application I created a KUTheme_simple folder under `src/main/resources/template` (optionally you can place it under `webapp`, e.g. `src/main/webapp/template` ). In that folder I created `checkboxlist.ftl` and copied the contents from `template.simple` `checkboxlist.ftl` (again found in the Struts core jar). After copying the contents to `checkboxlist.ftl` that is in `KUTheme_simple` folder, I modified `checkboxlist.ftl` so that the label tag has a style of red bold text and I added a break tag after each label so that each check box and label will be on its own line.

Since the XHTML theme is the default theme and I have a `theme.properties` file defined with `parent = xhtml`, the KUTheme will inherit all the themes from xhmtl except for the theme for the checkboxlist tag since my KUTheme includes a definition for that tag’s layout. In the `struts.xml` file (`src/main/resources`) you will see that the I’ve specified the default theme to be KUTheme.

In the deployed web application, Struts will first look for a tag’s template on the application’s class path and if it doesn’t find the template there it will use the default template that is part of the Struts core jar. Since we’ve added a template folder to the application’s web root, now when Struts creates the HTML to display the checkboxlist tag it will use the template that is in the KUTheme folder (which tells it to use the `checkboxlist.ftl` file that is in the KUTheme_simple folder instead of the one in the `template.simple` folder that is part of the Struts core Jar).

After redeploying the application the check boxes for the Car Models Owned should appear like:

## Summary

You can easily override the default theme used by Struts to control the appearance and layout of a Struts tag. Each Struts tag has an associated template file (e.g. `select.ftl`) that is in a folder named after the theme (e.g. xhtml). By default the Struts framework will look in the Struts core Jar file for the theme folder and templates. However, if you include your own theme folder (e.g. KUTheme) under webapp/template (or WebContent/template in the Ant version) and specify that folder name (e.g. KUTheme) as the value for the theme attribute, then the Struts framework will look in that theme folder for the tag’s template.

To learn more about how to use the Struts themes and how you can override them, visit Themes and Templates Documentation .

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