lucene的写索引的操作问题

lucene的写操作，默认的时候writer = new IndexWriter(indexDir, analyzer, override);当override为TRUE的时候，lucene将进行重写操作，override为FALSE的时候将是增量索引的过程，对于重复的文章仍旧重复索引的。

if (writer == null) {
   try {
    writer = new IndexWriter(indexDir, analyzer, override);
   } catch (IOException ioe) {
    throw new RuntimeException(ioe);
   }

   if (writer != null) {
    writer.setMaxMergeDocs(25);
    writer.setMaxBufferedDocs(25);
   }
  }