How can I use Jena to serialize RDF in the JSON syntax?

Not a direct answer, since you specifically want the Talis format, but the Jena-based code we use for the linked-data API json format (Talis were also part of developing that) is at: http://code.google.com/p/linked-data-api/source/browse/#svn/trunk/json-rdf

Some improvements and packaging for that are on the (infinite) todo list.

There is a RDF/JSON writer.

Ensure it is loaded:

SysRIOT.init()

then

model.write(System.out, "RDF/JSON") ;

Anything that has touched ARQ wil load it but the explicit init call is safe to call repeatedly.. This will soon be redundant but remain harmless.

SysRIOT augments Jena with the new parser and writers. It will become the standard set.

Not related to Talis format, but this is the first result to show on Google. With your result set, e.g. ResultSet resultSet = qe.execSelect();

Output to console

ResultSetFormatter.outputAsJSON(resultSet);

Write to a String

There is an overloaded outputAsJson method with an OutputStream as the first parameter. Use ByteArrayOutputStream to get the JSON into a String:

ByteArrayOutputStream b = new ByteArrayOutputStream();
ResultSetFormatter.outputAsJSON(b, resultSet);
String json = b.toString( );