code: public static Field getJoinRightTable(Class<?> clazz) {
  		if(clazz == null) {
  			throw new NoJoinTableMemberException("clazz is null");
  		}
  		List<Field> result = _getAnnotationColumns(clazz, JoinRightTable.class);
  		if(result == null || result.isEmpty()) {
  			throw new NoJoinTableMemberException("class " + clazz.getName()
  			    + " does not have @JoinRightTable field");
  		}
  		return result.get(0);
  	}
docs: 获得注解了@JoinRightTable的字段，如果没有注解，抛出NoJoinTableMemberException
  @param clazz
  @return