StandardAnalyzer analyzer = new StandardAnalyzer();
        IndexWriterConfig indexWriterConfig = new IndexWriterConfig(analyzer);
        IndexWriter indexWriter =
        		new IndexWriter(FSDirectory.open(Paths.get(Constants.index_dir)), indexWriterConfig);
        for(Document doc : documents) {
        	indexWriter.addDocument(doc);
        }
        indexWriter.commit();
        indexWriter.close();