Edit HTML Document with Java

I have an HTML document stored in memory (set on a Flying Saucer XHTMLPanel) in my java application.

xhtmlPanel.setDocument(Main.class.getResource("/mailtemplate/DefaultMail.html").toString());

html file below;

<html>
    <head>
    </head>
    <body>
        <p id="first"></p>
        <p id="second"></p>
    </body>
</html>

I want to set the contents of the p elements. I don't want to set a schema for it to use getDocumentById(), so what alternatives do I have?

Solution

XHTML is XML, so any XML parser would be my recommendataion. I maintain the JDOM library, so would naturally recommend using that, but other libraries, including the embedded DOM model in Java will work. I would use something like:

    Document doc = new SAXBuilder().build(Main.class.getResource("/mailtemplate/DefaultMail.html"));

    // XPath that finds the `p` element with id="first"
    XPathExpression<Element> xpe = XPathFactory.instance().compile(
            "//p[@id='first']", Filters.element());
    Element p = xpe.evaluateFirst(doc);

    p.setText("This is my text");

    XMLOutputter xout = new XMLOutputter(Format.getPrettyFormat());
    xout.output(doc, System.out);

Produces the following:

<?xml version="1.0" encoding="UTF-8"?>
<html>
  <head />
  <body>
    <p id="first">This is my text</p>
    <p id="second" />
  </body>
</html>