code: protected static void addFeatureThenClear(StringBuilder rawFeature, List<Integer> featureVector, FeatureMap featureMap)
      {
          int id = featureMap.idOf(rawFeature.toString());
          if (id != -1)
          {
              featureVector.add(id);
          }
          rawFeature.setLength(0);
      }
docs: 添加特征，同时清空缓存
  
  @param rawFeature
  @param featureVector
  @param featureMap