Starting Tomcat V8.5 Server at localhost has encountered a problem.

今天使用eclipse中的tomcate8.5发布工程，一开始没有问题，但是当我改了一下web.xml以后，再重新启动时，报以下的错误

Starting Tomcat v8.5 Server at localhost has encountered a problem.ServerTomcatv8.5Serveratlocalhostfailedtostart.

查看控制台，报

信息:StartingServletEngine:ApacheTomcat/8.5
java.lang.IllegalArgumentException:Servletmappingspecifiesanunknownservletnamestu_Login
atorg.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:3109)
atorg.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:3088)
atorg.apache.catalina.deploy.WebXml.configureContext(WebXml.java:1274)
atorg.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1326)
atorg.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:876)
atorg.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:317)
atorg.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
atorg.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:89)
atorg.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5061)
atorg.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
atorg.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1033)
atorg.apache.catalina.core.StandardHost.startInternal(StandardHost.java:774)
atorg.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
atorg.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1033)
atorg.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:291)
atorg.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
atorg.apache.catalina.core.StandardService.startInternal(StandardService.java:443)
atorg.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
atorg.apache.catalina.core.StandardServer.startInternal(StandardServer.java:727)
atorg.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
atorg.apache.catalina.startup.Catalina.start(Catalina.java:620)
atsun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethod)
atsun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
atsun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
atjava.lang.reflect.Method.invoke(Method.java:597)
atorg.apache.catalina.startup.Bootstrap.start(Bootstrap.java:303)
atorg.apache.catalina.startup.Bootstrap.main(Bootstrap.java:431)

刚开始以为端口被占用之类的，后来把能关的都关了还是不行，最后重启电脑还是不行，后来打开eclipse，clean一下，然后项目上右键-->properties-->找到project facets-->在右边选项卡中找到RunTimes-->选中ApacheTomcat v8.5，然后重新启动eclipse,成功了！