public void undeleteDocuments() {
   LuceneIndexReader reader = IndexReaderFactoryUtils.getIndexReader(indexFactory);
   try {
     reader.undeleteAll();
   } catch (IOException ex) {
     throw new LuceneIndexAccessException("Error during undeleting all documents.", ex);
   } finally {
     IndexReaderFactoryUtils.releaseIndexReader(indexFactory, reader);
   }
 }