Subject: [PATCH] Fix DISPLAY error on exporting org with plantuml to html

[Sun Lin <sunlin7@yahoo.com>]

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Hi,

When the environment variable "DISPLAY" is invalid, exporting plantuml block in org will got error message:
Exception in thread "main" java.awt.AWTError: Can't connect to X11 window server using 'localhost:11.0' as the value of the DISPLAY variable.
    at sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
...
To reproduce this issue, install the plantuml.jar and make sure it work inside org-mode.
Then open `/tmp/testing.org` and  input follow plantuml code and eval-expression `(progn (setenv "DISPLAY" "localhost:90")(org-html-export-to-html))`.
The root cause is org-mord execute the plantuml.jar in command line without headless parameter, then plantuml will try read the DISPLAY, it's unnecessary.
(For standalone plantuml, `org-plantuml-executable-args` has default value '-headless' to avoid reading DISPLAY).

Please help review the patch. Thanks.

Best Regards
Lin

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From 5e04a800691b04edd940dd124987336f6f30dd62 Mon Sep 17 00:00:00 2001
From: Lin Sun <lin.sun@zoom.us>
Date: Sat, 16 Oct 2021 03:01:18 +0000
Subject: [PATCH] Fix DISPLAY error on exporting org with plantuml to html

* org-babel-execute:plantuml: using headless mode for org calling plantuml for exporting to html
---
 lisp/ob-plantuml.el | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lisp/ob-plantuml.el b/lisp/ob-plantuml.el
index fc62160..7d92227 100644
--- a/lisp/ob-plantuml.el
+++ b/lisp/ob-plantuml.el
@@ -122,6 +122,7 @@ This function is called by `org-babel-execute-src-block'."
 				((not (file-exists-p org-plantuml-jar-path))
 				 (error "Could not find plantuml.jar at %s" org-plantuml-jar-path))
 				(t (list java
+					 "-Djava.awt.headless=true"
 					 "-jar"
 					 (shell-quote-argument (expand-file-name org-plantuml-jar-path))))))
 	 (full-body (org-babel-plantuml-make-body body params))
-- 
2.7.0