OK, I got it working.
Maybe this can help someone in the Future:
I used AtlassianWikiRenderer, for that I needed to add the JIRA-Core dependency in the POM.xml.
The code to render the Wiki annotated string to an HTML annotated string looks something like this:
AtlassianWikiRenderer atlassianWikiRenderer = new AtlassianWikiRenderer(eventPublisher, ComponentAccessor.getApplicationProperties(), velocityRequestContextFactory);
dataMap.put("commentHtml", atlassianWikiRenderer.render(comment.getBody(), new IssueRenderContext(issue)));
I’m putting this in to a map because I want to render the output with Velocity, that´s also the reason why the Key ends with “Html”, because when that´s the case Velocity is not going to escape the Stringand it is going to be displayed properly.
If someone else has a better Idea though, please let me know.