在学习struts 2时，为了方便，直接从下载的struts的apps目录下的struts2-blank.war压缩包下的WEB-INF\复制的web.xml，当我启动Tomcat时，发生
java.lang.IllegalArgumentException: <session-config> element is limited to 1 occurrence at org.apache.tomcat.util.descriptor.web.SetSessionConfig.begin(WebRuleSet.java:761) at org.apache.tomcat.util.digester.Digester.startElement(Digester.java:1180) at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanStartElement(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source) at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1448) at org.apache.tomcat.util.descriptor.web.WebXmlParser.parseWebXml(WebXmlParser.java:119) at org.apache.catalina.startup.ContextConfig.getDefaultWebXmlFragment(ContextConfig.java:1547) at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1113) at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:783) at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:307) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95) at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5213) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1408) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1398) at java.util.concurrent.FutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) 十二月 28, 2016 7:06:58 下午 org.apache.tomcat.util.descriptor.web.WebXmlParser parseWebXml 严重: Parse error in application web.xml file at file:/S:/leaning/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/conf/web.xml org.xml.sax.SAXParseException; systemId: file:/S:/leaning/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/conf/web.xml; lineNumber: 4678; columnNumber: 21; Error at (4678, 21) : <session-config> element is limited to 1 occurrence at org.apache.tomcat.util.digester.Digester.createSAXException(Digester.java:1891) at org.apache.tomcat.util.digester.Digester.createSAXException(Digester.java:1923) at org.apache.tomcat.util.digester.Digester.startElement(Digester.java:1183) at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanStartElement(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source) at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1448) at org.apache.tomcat.util.descriptor.web.WebXmlParser.parseWebXml(WebXmlParser.java:119) at org.apache.catalina.startup.ContextConfig.getDefaultWebXmlFragment(ContextConfig.java:1547) at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1113) at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:783) at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:307) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95) at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5213) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1408) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1398) at java.util.concurrent.FutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: java.lang.IllegalArgumentException: <session-config> element is limited to 1 occurrence at org.apache.tomcat.util.descriptor.web.SetSessionConfig.begin(WebRuleSet.java:761) at org.apache.tomcat.util.digester.Digester.startElement(Digester.java:1180) ... 26 more
这让我很慌啊，从没见过的，后来认真阅读错误，发现/D:/leaning/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/conf/web.xml; lineNumber: 4678; columnNumber: 21; Error at (4678, 21) : <session-config> element is limited to 1 occurrence
根据描述的找到文件/D:/leaning/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/conf/web.xml，果然有两个session-conf
<session-config>
<session-timeout>30</session-timeout>
</session-config>
删除一个，在重启Tomcat，问题解决。