web.xml的问题：报错如下
org.apache.commons.digester.Digester error
严重: Parse Error at line 137 column 11: The content of element type "web-app" must match "(icon?,display-name?,description?,distributable?,context-param*,filter*,filter-mapping*,listener*,servlet*,servlet-mapping*,session-config?,mime-mapping*,welcome-file-list?,error-page*,taglib*,resource-env-ref*,resource-ref*,security-constraint*,login-config?,security-role*,env-entry*,ejb-ref*,ejb-local-ref*)".
org.xml.sax.SAXParseException: The content of element type "web-app" must match "(icon?,display-name?,description?,distributable?,context-param*,filter*,filter-mapping*,listener*,servlet*,servlet-mapping*,session-config?,mime-mapping*,welcome-file-list?,error-page*,taglib*,resource-env-ref*,resource-ref*,security-constraint*,login-config?,security-role*,env-entry*,ejb-ref*,ejb-local-ref*)".
at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
at org.apache.xerces.util.ErrorHandlerWrapper.error(Unknown Source)
at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
at org.apache.xerces.impl.dtd.XMLDTDValidator.handleEndElement(Unknown Source)
at org.apache.xerces.impl.dtd.XMLDTDValidator.endElement(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanEndElement(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.DTDConfiguration.parse(Unknown Source)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
at org.apache.commons.digester.Digester.parse(Digester.java:1548)
at org.apache.catalina.startup.ContextConfig.applicationConfig(ContextConfig.java:220)
at org.apache.catalina.startup.ContextConfig.start(ContextConfig.java:579)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:181)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:3523)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:774)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:760)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:548)
at org.apache.catalina.core.StandardHostDeployer.install(StandardHostDeployer.java:260)
at org.apache.catalina.core.StandardHost.install(StandardHost.java:741)
at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:512)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:354)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:671)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1149)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:707)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1141)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:316)
at org.apache.catalina.core.StandardService.start(StandardService.java:450)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:2143)
at org.apache.catalina.startup.Catalina.start(Catalina.java:463)
at org.apache.catalina.startup.Catalina.execute(Catalina.java:350)
at org.apache.catalina.startup.Catalina.process(Catalina.java:129)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:156)
后来查了下，是因为这个原因：
XML 对大小写是很敏感的，对顺序虽然不敏感但它可以对错序的情况报错。
<servlet>一定要在所有的<servlet-mapping>前面，不然就会报如上错误，改变位置后问题解决
