Fixing PlantUML in org-babel

I was receiving this error:

Exception in thread "main" java.awt.AWT Error: Can't connect to X11 window server using ':1' as the value of the DISPLAY variable.

Seems to be because it isn't running headless. Which, from plantuml-java-args, it looks like it should be. However, when running via babel, it appears those args aren't used?

I made a fix by editing \~/.emacs.d/elpa/26.3/develop/org-plus-contrib-20201116/ob-plantuml.el and adding in "-Djava.awt.headless=true" to the args passed to the jar.

Changing:

(t (list java
	 "-jar"
	 (shell-quote-argument (expand-file-name org-plantuml-jar-path))))))

to

(t (list java
	 "-jar -Djava.awt.headless=true"
	 (shell-quote-argument (expand-file-name org-plantuml-jar-path))))))

But this is temporary - it will be overwritten when org-plus-contrib package is updated.

And how come it was working a couple of weeks ago - what changed?

[2022-06-04 Sat]

Shared by Liban via email:

I was digging around trying to find out how to get PlantUML to work in org-babel in headless mode and came across your blog post. It prompted me to have a look at the source and found that you can add java arguments in the plantuml babel header[1], so something like:

#+begin_src plantuml :file diagram.svg :java -Djava.awt.headless=true

worked for me. Theres also a org-babel-default-header-args:plantuml variable to set things as default but I haven't tried that yet (only the one diagram for me so far).