Spring Boot: Thymeleaf Template Decorator

In this post, we take a look at how you can reuse a header and footer across all Thymeleaf templates with some help from Spring Boot's auto-configuraiton.

Mohamed Sanaulla

Nov. 29, 17 · Tutorial

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The question of reusing headers and footers on all Thymeleaf templates has been often been asked on StackOverflow. In this article, I will show you how you can structure templates using the Thymeleaf Layout Dialect to achieve a higher code reusability in a Spring Boot application.

Create a Spring Boot Application

Let's use Spring Initializer to create an empty project with the required dependencies. I chose the following for the empty project:

Once you load the project in your favorite IDE, just update the thymeleaf and thymeleaf-layout-dialect version to the following in your project’s pom.xml:

<thymeleaf-layout-dialect.version>2.2.2</thymeleaf-layout-dialect.version>
<thymeleaf.version>3.0.9.RELEASE</thymeleaf.version>

Note: I have used Spring Boot 1.5.8.RELEASE in this sample.

Defining Base Template

If we are using Spring Boot, we do not have to configure anything to use Thymeleaf and Thymeleaf Layout Dialect. The auto-configuration support will configure all the required beans for using Thymeleaf templates.

Let’s create a base.html at the location src\main\resources\templates:

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
  xmlns:th="http://www.thymeleaf.org"   
  xmlns:layout="http://www.ultraq.net.nz/thymeleaf/layout">
  <head>
 
    <title layout:title-pattern="$CONTENT_TITLE - $LAYOUT_TITLE">Base</title>
    <meta name="description" content=""/>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
 
    <link rel="stylesheet" type="text/css" 
      href="https://bootswatch.com/4/cerulean/bootstrap.min.css" />
  </head>
  <body>
 
    <nav class="navbar navbar-light bg-light">
      <span class="navbar-brand mb-0 h1">Decorator Sample</span>
    </nav>
 
    <div class="container">
      <nav aria-label="breadcrumb" role="navigation">
        <ol class="breadcrumb">
          <th:block layout:fragment="breadcrumb">
          </th:block>
        </ol>
      </nav>
      <div class="content">
        <div layout:fragment="page_content"></div>
      </div>
    </div>
    <!-- /.container -->
 
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js">
    </script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js">
    </script>
    <th:block layout:fragment="scripts">
    </th:block>
  </body>
 
</html>

In the above base.html, you can see there are three placeholders:

Breadcrumbs
Content
JavaScript required for content

The rest of the Thymeleaf templates decorate using base.html and provide required data for just the three placeholders. Those will be seen in the subsequent sections. The title for the page is defined as layout:title-pattern="$CONTENT_TITLE - $LAYOUT_TITLE" which means that if any template declares a My Page tag, then the page title becomes Base - My Page.

Content for Breadcrumbs

Any page that wishes to decorate itself using base.html should declare in their HTML as shown below:

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" 
  xmlns:th="http://www.thymeleaf.org" 
  xmlns:layout="http://www.ultraq.net.nz/thymeleaf/layout" 
  layout:decorate="~{base}">
</html>

The layout:decorate attribute takes the location of the base template with respect to the templates root folder. In our case, the templates root folder is src/main/resources/templates.

We can provide the content for breadcrumb by writing the following HTML:

<th:block layout:fragment="breadcrumb">
  <li class="breadcrumb-item">Page 1</li>
</th:block>

Ideally, following the order in which the layout:fragment are defined in the base template will help in maintaining consistency in content order among the pages. The final HTML generated by Thymeleaf and its layout dialect is:

<nav aria-label="breadcrumb" role="navigation">
  <ol class="breadcrumb">
    <li class="breadcrumb-item">Page 1</li>
  </ol>
</nav>

Populating the `page_content`

Along similar lines, the content for page_content will be:

<div layout:fragment="page_content" id="page_content">
  <h3>Page 1</h3>
 
  <div class="alert alert-info" style="display: none;" 
    id="js-content">
  </div>
  <a th:href="@{/page2}">Go to page 2</a>
</div>

Use of <th></th> will remove the need for using a dummy tag just to wrap the content. If we need to wrap the content in a specific element, like we have used <div> above, the <th></th> has to be replaced with the specific element.

Populating the `scripts`

A few may question the need for the scripts placeholder. This allows us to keep the page-related JavaScript in one place and not pollute all the JavaScript in the base template.

<th:block layout:fragment="scripts">
<script type="text/javascript">
$(function(){
    $("#js-content").html("From Javascript").slideToggle();
});
</script>
</th:block>

You can even create a dedicated .js file and link it in the scripts section:

<th:block layout:fragment="scripts">
<script type="text/javascript"
    src="@{/path/to/js/file}">
</script>
</th:block>

Conclusion

In this article, we saw how to use Thymeleaf Layout Dialect to decorate the templates with a common base template. We didn’t have to do any configuration, as Spring Boot does it via the auto-configuration when relevant libraries are on its classpath, which, in this case, are the dependencies brought in by the starter pom spring-boot-starter-thymeleaf

The working Spring Boot sample can be found here.

Spring Framework Spring Boot Template Thymeleaf

Published at DZone with permission of Mohamed Sanaulla, DZone MVB. See the original article here.

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