/** User drills down on 'Publish Year/2010'. */
private List<FacetResult> drillDown() throws IOException {
DirectoryReader indexReader = DirectoryReader.open(indexDir);
IndexSearcher searcher = new IndexSearcher(indexReader);
SortedSetDocValuesReaderState state = new SortedSetDocValuesReaderState(indexReader);
// Now user drills down on Publish Year/2010:
FacetSearchParams fsp = new FacetSearchParams(new CountFacetRequest(new CategoryPath("Author"), 10));
DrillDownQuery q = new DrillDownQuery(fsp.indexingParams, new MatchAllDocsQuery());
q.add(new CategoryPath("Publish Year/2010", '/'));