Preview in plantuml-mode on macOS Emacs

I encountered 2 issues to preview in plantuml-mode on macOS Emacs. I resolved them but please tell me if you have better solution.

TL;DR

• Upgrade your Java runtime to resolve CoreText warnings to stdout
• Disable headless option
  • For plantuml-mode example

(setq plantuml-default-exec-mode 'jar)
(with-eval-after-load 'plantuml
  (setq plantuml-java-args
    (delete "-Djava.awt.headless=true" plantuml-java-args)))

Issues

• There are 2 issues I encountered when using preview (C-c C-c) in plantuml-mode

Preview corruption

Cause

• It is caused by CoreText warnings from java command to stdout
  • plantuml-mode gets preview images via stdout
  • Warnings to stdout corrupts that behaviour
  • [JDK-8244621] [macos10.15] Garbled FX printing plus CoreText warnings on Catalina when building with Xcode 11 - Java Bug System

Solution

• It has been resolved later version of Java runtime, so it can be solution to upgrade your Java environment
  • If you installed openjdk with brew, you can use brew upgrade openjdk
  • You have to consider because it may cause seemingly unrelated issue by upgrading your Java environment

headless exception

Information

• Exception in thread "main" java.awt.HeadlessException · Issue #275 · plantuml/plantuml · GitHub

Workaround

• Disable passing -headless option to plantuml
  • plantuml-mode passes it to plantuml as default, so disable it
    • One of examples to disable it, put the codes at TL;DR into your Emacs configuration file

(setq plantuml-default-exec-mode 'jar)
(with-eval-after-load 'plantuml
  (setq plantuml-java-args
    (delete "-Djava.awt.headless=true" plantuml-java-args)))

• If using via plantuml command, add -gui option
  • plantuml command automatically adds -Djava.awt.headless=true if -gui is not specified