code: public Map<String, String> getFieldMap() {
  		if (headerMap == null) {
  			throw new IllegalStateException("No header available");
  		}
  
  		final Map<String, String> fieldMap = new LinkedHashMap<>(headerMap.size());
  		String key;
  		Integer col;
  		String val;
  		for (final Map.Entry<String, Integer> header : headerMap.entrySet()) {
  			key = header.getKey();
  			col = headerMap.get(key);
  			val = null == col ? null : get(col);
  			fieldMap.put(key, val);
  		}
  
  		return fieldMap;
  	}
docs: 获取标题与字段值对应的Map
  
  @return an unmodifiable map of header names and field values of this row
  @throws IllegalStateException CSV文件无标题行抛出此异常