Tomcat中出现Server Tomcat v9.0 Server at localhost failed to start.解决办法

1.错误提示

 A child container failed during startjava.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/day02]]    at java.util.concurrent.FutureTask.report(Unknown Source)    at java.util.concurrent.FutureTask.get(Unknown Source)    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:947)    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:839)    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1425)    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1415)    at java.util.concurrent.FutureTask.run(Unknown Source)    at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)    at java.util.concurrent.AbstractExecutorService.submit(Unknown Source)    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:941)    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:258)    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:422)    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:770)    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)    at org.apache.catalina.startup.Catalina.start(Catalina.java:657)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)    at java.lang.reflect.Method.invoke(Unknown Source)    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:355)    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:495)Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/day02]]    at org.apache.catalina.util.LifecycleBase.handleSubClassException(LifecycleBase.java:441)    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:198)    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1425)    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1415)    at java.util.concurrent.FutureTask.run(Unknown Source)    at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)    at java.util.concurrent.AbstractExecutorService.submit(Unknown Source)    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:941)    ... 21 moreCaused by: java.lang.NoClassDefFoundError: org/springframework/web/context/WebApplicationContext    at java.lang.Class.getDeclaredFields0(Native Method)    at java.lang.Class.privateGetDeclaredFields(Unknown Source)    at java.lang.Class.getDeclaredFields(Unknown Source)    at org.apache.catalina.util.Introspection.getDeclaredFields(Introspection.java:110)    at org.apache.catalina.startup.WebAnnotationSet.loadFieldsAnnotation(WebAnnotationSet.java:262)    at org.apache.catalina.startup.WebAnnotationSet.loadApplicationServletAnnotations(WebAnnotationSet.java:136)    at org.apache.catalina.startup.WebAnnotationSet.loadApplicationAnnotations(WebAnnotationSet.java:66)    at org.apache.catalina.startup.ContextConfig.applicationAnnotationsConfig(ContextConfig.java:328)    at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:778)    at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:299)    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:123)    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5003)    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)    ... 27 moreCaused by: java.lang.ClassNotFoundException: org.springframework.web.context.WebApplicationContext    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1269)    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1104)    ... 40 more

解决办法：
缺少了一个jar包
把这个jar包加进去就可以了，根本不是Tomcat的问题。
遇到这种问题时，要记得把正在测试的项目去除掉，去换一下以前调试正常的项目，如果没有问题，说明此种问题是正在测试项目的原因，不是Tomcat的原因，学会排除问题，走对方向是关键。
而且要细心，不要大意！