Parse Fatal Error at line 2 column 243: 已经为元素 "web-app" 指定属性 "xmlns"

异常信息：

严重: Parse Fatal Error at line 2 column 243: 已经为元素 "web-app" 指定属性 "xmlns"。

org.xml.sax.SAXParseException; systemId: file:/D:/yongqian.liu/grid/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/grid/WEB-INF/web.xml; lineNumber: 2; columnNumber: 243; 已经为元素 "web-app" 指定属性 "xmlns"。
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:203)
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(ErrorHandlerWrapper.java:177)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:400)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:327)
at com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(XMLScanner.java:1437)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanAttribute(XMLDocumentFragmentScannerImpl.java:1561)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanStartElement(XMLDocumentFragmentScannerImpl.java:1320)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$ContentDriver.scanRootElementHook(XMLDocumentScannerImpl.java:1295)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:3135)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:880)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:848)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)
at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1451)
at org.apache.tomcat.util.descriptor.web.WebXmlParser.parseWebXml(WebXmlParser.java:120)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1107)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:771)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:305)
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:5154)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
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(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

 

问题原因：

web.xml 文件中：

xmlns="http://java.sun.com/xml/ns/javaee"

重复了，删除即可。