How read and write triples to `Graph` at the same time?

[Евгений = )]

Hello again!
I need to do next staff: read all "name" fields from MY_TDB, do some
calculations with this "name" and save results to MY_TDB.
But I need to read and save on the fly, eg read on "name" -> do calculaions
-> save results -> read next "name" -> calculations -> save result ...

Here is the example code:
public class TestTdbTransactionsReadWrite {
    public static void main(String[] args) {
        Dataset dataset = TDBFactory.createDataset();
        dataset.begin(ReadWrite.WRITE);
        DatasetGraph datasetGraph = dataset.asDatasetGraph();
        Graph graph = datasetGraph.getDefaultGraph();

        // Fill graph.
        graph.add(
            new Triple(
                NodeFactory.createURI("http://example/unit13";),
                NodeFactory.createURI("http://example/name";),
                NodeFactory.createLiteral("Unit 13", "en")
            )
        );

        graph.add(
            new Triple(
                NodeFactory.createURI("http://example/unit13";),
                NodeFactory.createURI("http://example/type";),
                NodeFactory.createURI("http://example/robot";)
            )
        );

        graph.add(
            new Triple(
                NodeFactory.createURI("http://example/unit13";),
                NodeFactory.createURI("http://example/creationYear";),
                NodeFactory.createURI("http://example/2015";)
            )
        );

        // Test.
        String qs1 = "SELECT * { ?s <http://example/name> ?o }";
        try (QueryExecution qExec = QueryExecutionFactory.create(qs1,
dataset)) {
            ResultSet rs = qExec.execSelect();

            while (rs.hasNext()) {
                QuerySolution qs = rs.next();
                RDFNode nodeSubject = qs.get("s");
                RDFNode nodeObject = qs.get("o");
                if (nodeSubject.isURIResource() && nodeObject.isLiteral()) {
                    String str = nodeObject.asLiteral().getString();

                    graph.add(
                        new Triple(

NodeFactory.createURI(nodeSubject.asResource().getURI()),
                            NodeFactory.createURI("http://example/value";),

NodeFactory.createLiteral(String.valueOf(str.length()))
                        )
                    );
                }
            }

            dataset.commit();
        } finally {
            dataset.end();
        }

        RDFDataMgr.write(System.out, graph, RDFFormat.NTRIPLES);
    }
}

https://github.com/Hronom/test-jena