/**
  * 通过ds来对应field
  *
  * @param ds
  * @return
  */
 private Map<String, Integer> getIndexMap(Dataset ds) {
   Map<String, Integer> indexMap = new HashMap<String, Integer>();
   int count = ds.getFieldSet().getFieldCount();
   for (int i = 0; i < count; i++) {
     Field field = ds.getFieldSet().getField(i);
     String key = field.getId();
     indexMap.put(key, i);
   }
   return indexMap;
 }