解决maven工程中出现The project was not built since its build path is incomplete. Cannot find the class file

错误描述：The project was not built since its build path is incomplete. Cannot find the class file for org.apache.commons.beanutils.Converter.

解决办法：在maven仓库中把commons-beanutils文件下的所有的文件全部删掉，然后更新maven工程，选中project-->maven-->update project，让maven重新down下依赖，然后就可以了，估计是由于在maven down依赖的时候出现中断，然后jar包里面的类不全导致的。