code: protected List<String> preprocess(String document)
      {
          List<Term> termList = segment.seg(document);
          ListIterator<Term> listIterator = termList.listIterator();
          while (listIterator.hasNext())
          {
              Term term = listIterator.next();
              if (CoreStopWordDictionary.contains(term.word) ||
                  term.nature.startsWith("w")
                  )
              {
                  listIterator.remove();
              }
          }
          List<String> wordList = new ArrayList<String>(termList.size());
          for (Term term : termList)
          {
              wordList.add(term.word);
          }
          return wordList;
      }
docs: 重载此方法实现自己的预处理逻辑（预处理、分词、去除停用词）
  
  @param document 文档
  @return 单词列表