public static long count(IndexSearcher searcher, Query query) throws IOException {
TotalHitCountCollector countCollector = new TotalHitCountCollector();
// we don't need scores, so wrap it in a constant score query
if (!(query instanceof ConstantScoreQuery)) {
query = new ConstantScoreQuery(query);
}
searcher.search(query, countCollector);
return countCollector.getTotalHits();
}