@Override
      public void run() {
        StyledDocument styleDoc = conversationDisplayArea.getStyledDocument();
        HTMLDocument doc = (HTMLDocument) styleDoc;
        Element last = doc.getParagraphElement(doc.getLength());
        try {
          doc.insertBeforeEnd(last, builder.toString());
        }
        catch (BadLocationException | IOException e) {
          // message display failed
        }
      }