Since Asciidoctor 1.5.0 we can use extensions when we write AsciiDoc documents. These extensions can be written in Ruby or any JVM language. If we use Gradle and the Asciidoctor Gradle plugin to transform our documents we can use both extensions. Of course an extension written in for example Java or Groovy can be included as a regular dependency in our build configuration. As the extension is on the classpath of the asciidoctor task then it can be used. When the extension is a Ruby extension and available as a Ruby gem we need some more configuration in our build file. To use an Asciidoctor extension written in Ruby in our build we must first make sure that we can download the extension. Then we can configure the asciidoctor task from the Asciidoctor Gradle plugin to use the extension.

Let's start with a sample Asciidoctor document which uses the Asciidoctor Diagram extension. With this extension we can embed diagrams as text in our document and get graphical images as output.

= Sample diagram

:imagesdir: images

== Ditaa

// Sample diagram from Asciidoctor Diagram website

[ditaa, "asciidoctor-diagram-process"]
                   | Asciidoctor |-------+
                   |   diagram   |       |
                   +-------------+       | PNG out
                       ^                 |
                       | ditaa in        |
                       |                 v
 +--------+   +--------+----+    /---------------\
 |        |---+ Asciidoctor +--->|               |
 |  Text  |   +-------------+    |   Beautiful   |
 |Document|   |   !magic!   |    |    Output     |
 |     {d}|   |             |    |               |
 +---+----+   +-------------+    \---------------/
     :                                   ^
     |          Lots of work             |

Next we create our Gradle build file. We must apply the Asciidoctor Gradle plugin so we can transform our AsciiDoc documents. And we must apply the JRuby Gradle plugin so we can download Ruby gems and use them from the asciidoctor task. The JRuby plugin adds a gems dependency configuration, which we can use to define the Ruby gems we need. The task jrubyPrepareGems is also added by the plugin and this task will download the gems and extract them in our project build directory. In our asciidoctor task that is added by the Asciidoctor plugin we use the requires property to specify which gem is needed. We also set the gemPath property to the directory which contains the downloaded and extracted Ruby gems. The following build file defines the plugins and configures the tasks we need so we can use Asciidoctor Diagram:

buildscript {
    repositories {

    dependencies {
        classpath 'org.asciidoctor:asciidoctor-gradle-plugin:1.5.0'
        classpath 'com.github.jruby-gradle:jruby-gradle-plugin:0.1.5'

// Plugin so we can render AsciiDoc documents.
apply plugin: 'org.asciidoctor.gradle.asciidoctor'
// Plugin so we can use Ruby gems when rendering documents.
apply plugin: 'com.github.jruby-gradle.base'

dependencies {
    // gems dependency configuration is added by
    // jruby-gradle-plugin. Here we define
    // the gems we need in our build.
    gems 'rubygems:asciidoctor-diagram:1.2.0'

asciidoctorj {
    // We can change the AsciidoctorJ
    // dependency version.
    version = '1.5.1'

asciidoctor {
    // jrubyPrepareGems task is added by the JRuby
    // plugin and will download Ruby gems we have
    // defined in the gems dependency configuration.
    dependsOn jrubyPrepareGems

    // Asciidoctor task needs the
    // asciidoctor-diagram gem, we installed
    // with the jrubyPrepareGems task and
    // gems dependency configuration.
    requires = ['asciidoctor-diagram']

    // Set path to find gems to directory
    // used by jrubyPrepareGems task.
    gemPath = jrubyPrepareGems.outputDir

defaultTasks 'asciidoctor'

To generate our sample document we only have to run $ gradle from the command line. After the documents are generated we can the result in the build/asciidoc directory of our project. The following screenshot shows the generated HTML:

Written with Asciidoctor 1.5.1 and Gradle 2.1.

Original article