org.apache.catalina.LifecycleException: Failed to start component异常解决办法

最近在写servlet时碰到了以下异常：
十二月 09, 2018 9:40:37 下午 org.apache.catalina.core.ContainerBase startInternal

严重: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/day07]]
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:949)
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.ContainerBaseStartChild.call(ContainerBase.java:1427)atorg.apache.catalina.core.ContainerBaseStartChild.call(ContainerBase.java:1427) at org.apache.catalina.core.ContainerBaseStartChild.call(ContainerBase.java:1427)atorg.apache.catalina.core.ContainerBaseStartChild.call(ContainerBase.java:1417)
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:943)
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:682)
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:350)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:492)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/day07]]
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.ContainerBaseStartChild.call(ContainerBase.java:1427)atorg.apache.catalina.core.ContainerBaseStartChild.call(ContainerBase.java:1427) at org.apache.catalina.core.ContainerBaseStartChild.call(ContainerBase.java:1427)atorg.apache.catalina.core.ContainerBaseStartChild.call(ContainerBase.java:1417)
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:943)
… 21 more
Caused by: java.lang.IllegalArgumentException: Invalid [aa] in servlet mapping
at org.apache.catalina.core.StandardContext.addServletMappingDecoded(StandardContext.java:3120)
at org.apache.catalina.Context.addServletMappingDecoded(Context.java:879)
at org.apache.catalina.startup.ContextConfig.configureContext(ContextConfig.java:1376)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1187)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:765)
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:4989)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
… 27 more

最后确定是WEB-INF/web.xml文件配置错误导致。

注意。其中，url-pattern要以"/"开始。