code: public static Field getFieldByDBField(Class<?> clazz, String dbFieldName) {
  		List<Field> fields = getColumns(clazz);
  		for(Field field : fields) {
  			Column column = field.getAnnotation(Column.class);
  			if(column.value().equals(dbFieldName)) {
  				return field;
  			}
  		}
  		return null;
  	}
docs: 从db字段名拿字段对象
  @param clazz
  @param dbFieldName
  @return 如果不存在返回null