错误提示:

org.hibernate.MappingException: Unknown entity: org.dao.po.Role
    at org.hibernate.internal.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:1096)
    at org.hibernate.internal.SessionImpl.getEntityPersister(SessionImpl.java:1443)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:116)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:209)
    at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:55)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:194)
    at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:49)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
    at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:715)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:707)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:702)
    at org.dao.HibernateTest.main(HibernateTest.java:18)

可能原因

1. 引入的entity包有错误,应该引入: import javax.persistence.Entity;
2. 没有在hibernate.cfg.xml中指定注解类<mapping class="org.dao.po.Role" />

备注:

如果使用配置文件配置pojo,那么在hibernate.cfg.xml文件中应该是引入文件<mapping resource="org/dao/po/Role.hbm.xml"></mapping>
如果是使用注解,参考上面第二条