Register a Ruby Extension

You can even register extensions written in Ruby using AsciidoctorJ. To register a Ruby extension you must get a RubyExtensionRegistry class instead of JavaExtensionRegistry.

RubyExtensionRegistry rubyExtensionRegistry = this.asciidoctor.rubyExtensionRegistry(); (1)
rubyExtensionRegistry.loadClass(Class.class.getResourceAsStream("/YellRubyBlock.rb")).block("rubyyell", "YellRubyBlock"); (2)

String content = asciidoctor.convertFile(new File(
                "target/test-classes/sample-with-ruby-yell-block.ad"),
                Opions.builder().toFile(false).build());

1	`rubyExtensionRegistry` method is called to get a RubyExtensionRegistry instance.
2	Ruby file containing a class implementing a Block extension is loaded inside the Ruby runtime. Then the block is registered with a name (rubyyell), and we pass the name of the class to be instantiated.

YellBlock.rb

require 'asciidoctor'
require 'asciidoctor/extensions'

class YellRubyBlock < Asciidoctor::Extensions::BlockProcessor
  option :contexts, [:paragraph]
  option :content_model, :simple

  def process parent, reader, attributes
    lines = reader.lines.map {|line| line.upcase.gsub(/\.( |$)/, '!\\1') }
    Asciidoctor::Block.new parent, :paragraph, :source => lines, :attributes => attributes
  end
end