Java. lang. RuntimeException: Invalid action class configuration that references an unknown class named was found online. The most common cause is that the configuration file or field is wrong. The ClassNotFound error is also prompted. Think about the struts2 configuration. The default mode is sington. If you do not configure it in spring. If you want to log on to multiple users at the same time, this exception will occur. You can change the scope of spring to the prototype attribute. Solution: Pay attention to Case sensitivity. The action on the page is consistent with the action of struts, and the class of struts is consistent with the bean of spring. Second, ensure that the configuration of spring is correct. Third, pay attention to struts. configure the success of the result in xml !! (Most people make an error here) Fourth: The input configuration must be added for result verification.