Building the XHTML Extension

You can either build the XHTML extension with the org.w3c.dom.Element or pass XHTML directly as String.

First create a Document:

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = dbf.newDocumentBuilder();
Document doc = builder.newDocument();

Then create the HTML extension with that document, get the body element and assemble your HTML with DOM operations. Make sure to use valid HTML tags, especially those defined in XEP-0071: XHTML-IM!

Html html = new Html(doc);
Element body = html.getBody();
Element p = doc.createElement("p");
p.setAttribute("style", "font-weight:bold");

Then add the extension:

Message message = new Message(Jid.of("romeo@example.im", "Hi!"));

Alternatively you can pass valid XHTML (which will be appended to the <body> element), directly as String to the constructor:

Html html = new Html("<p style=\"font-weight:bold\">Hi!</p>");

Both will result in the following message:

<message to="romeo@example.im">
  <html xmlns="http://jabber.org/protocol/xhtml-im">
    <body xmlns="http://www.w3.org/1999/xhtml">
      <p style="font-weight:bold">Hi!</p>

Getting the HTML Extension

Html html = message.getExtension(Html.class);
if (html != null) {
    // html.getBody()
    // html.getContent()

Use either getBody() which gets the body element as DOM Element or getContent(), which gets the XHTML content (between the <body> element) as String.