Emacs

From the original work by Zhang Weize, plantuml-mode supports editing and previewing PlantUML diagrams all within Emacs, optionally also integrating with Org-Babel.

Luca Greco has shared a set of standalone helpers to edit, render, preview PlantUML code from Emacs.

Org-Babel

Org-Babel now natively supports blocks of plantuml code.

Napkin

ob-napkin package is available from MELPA.

ob-napkin supports Python syntax for sequence diagrams along with the plain plantuml code. Note that it uses Plantuml server, which means that it does not require to install JAR file and usually faster than invoking JVM.

Emacs Org-Mode

1.) Download plantuml.jar from official download page and save it at /home/you/path/to/plantuml.jar

2.) install plantuml-mode via melpa.

3.) in *scratch* execute

(setq org-plantuml-jar-path (expand-file-name "/home/you/path/to/plantuml.jar"))
(add-to-list 'org-src-lang-modes '("plantuml" . plantuml))
(org-babel-do-load-languages 'org-babel-load-languages '((plantuml . t)))

4.) put some uml in your org file e.g.

#+begin_src plantuml :file my-diagram.png
title Authentication Sequence

Alice->Bob: Authentication Request
note right of Bob: Bob thinks about it
Bob->Alice: Authentication Response
#+end_src

5.) export e.g. with C-c C-e h o

ob-plantuml.el (obsolete)

You can also use PlantUML with Emacs org-mode.

You will find the needed macro at the following address http://www.emacswiki.org/emacs/IanYang

Once installed, embed PlantUML code in Emacs org-mode is used like this:

#+BEGIN_UML
Alice -> Bob: Authentication Request
Bob --> Alice: Authentication Response
#+END_UML

While the org file is exported to HTML or other formats, PlantUML is called to generate image and replace the block in place.

Thanks to Ian Yang for the work done.

This method, however, is considered obsolete: > ;; OBSOLETED, use ob-plantuml.el bundled in org instead. ( A citation from https://www.emacswiki.org/emacs/org-export-blocks-format-plantuml.el )