We use Castor (http://www.castor.org/) to accomplish this. We've been
using it with XSDs, but there may be support for DTDs as well (haven't
checked). If not, it's open source, so you can add in support for DTDs, or
you can get a DTD to XSD converter.

   - Oliver

A) database persistance is something you might want to look into, check
out hybernate.

B) try xmlbeans, in summary it takes a schema and compiles a package of
java classes that are bound to the schema definition, and methods that
allow serialization and parsing of xml text.

C) [your example] this looks like DOM.
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

DocumentBuilder builder factory.newDocumentBuilder();

Document doc = builder.newDocument;

Element a = doc.createElement("A");
doc.appendChild(a);

Element b = doc.createElement("B");
a.appendChild(b);

Element c = doc.createElement("C");
c.appendChild(doc.createText("cccccc"));
b.appendChild(c);

Element d = doc.createElement("D");
d.appendChild(doc.createText("dddddd"));
b.appendChild(d);

is an example in DOM howto generate what you want.

those methods are utterly trivial. If you don't want syntax checking
for balance, and other restrictions, you could implement them each
with a println statement.  You then can avoid downloading an XML
library.