問題：Incompatible types. Required List<Teacher> but 'query' was inferred to T: no instance(s) of type variable(s) exist so that Teacher conforms to List<Teacher>
不兼容的類型。必需的List<Teacher>但是'query'被推斷為T:不存在類型變量的實例，因此Teacher符合List<Teacher>
解決方法：
List<Teacher> teachers= (List<Teacher>)
queryRunner.query(DbUtils.getConnection(),"select * from teacher;",new BeanHandler<Teacher>(Teacher.class));