情景描述：
昨天晚上Tomcat生产环境部署完应用程序之后，Tomcat可以正常启动，应用程序新发布的功能也可以正常使用。但在查看Tomcat日志时，发现有些错误信息（a million sentence of mmp in my heart ！o(╥﹏╥)o），为了防止后续对应用程序造成影响，还是把坑填了吧（I have a heart of gold！^_^ ）。
问题描述：
21-Feb-2019 23:08:23.678 SEVERE [main] org.apache.tomcat.util.digester.Digester.fatalError Parse Fatal Error at line 46 column 2: The markup in the document following the root element must be well-formed.
org.xml.sax.SAXParseException; lineNumber: 46; columnNumber: 2; The markup in the document following the root element must be well-formed.
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:1472)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$TrailingMiscDriver.next(XMLDocumentScannerImpl.java:1395)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:602)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:505)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:841)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:770)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)
at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1470)
at org.apache.catalina.users.MemoryUserDatabase.open(MemoryUserDatabase.java:416)
at org.apache.catalina.users.MemoryUserDatabaseFactory.getObjectInstance(MemoryUserDatabaseFactory.java:102)
at org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:94)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
at org.apache.naming.NamingContext.lookup(NamingContext.java:841)
at org.apache.naming.NamingContext.lookup(NamingContext.java:152)
at org.apache.naming.NamingContextBindingsEnumeration.nextElementInternal(NamingContextBindingsEnumeration.java:117)
at org.apache.naming.NamingContextBindingsEnumeration.next(NamingContextBindingsEnumeration.java:71)
at org.apache.naming.NamingContextBindingsEnumeration.next(NamingContextBindingsEnumeration.java:34)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.createMBeans(GlobalResourcesLifecycleListener.java:138)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.createMBeans(GlobalResourcesLifecycleListener.java:110)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.lifecycleEvent(GlobalResourcesLifecycleListener.java:82)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:394)
at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:339)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:780)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
21-Feb-2019 23:08:23.680 WARNING [main] org.apache.naming.NamingContext.lookup Unexpected exception resolving reference
org.xml.sax.SAXParseException; lineNumber: 46; columnNumber: 2; The markup in the document following the root element must be well-formed.
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1239)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)
at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1470)
at org.apache.catalina.users.MemoryUserDatabase.open(MemoryUserDatabase.java:416)
at org.apache.catalina.users.MemoryUserDatabaseFactory.getObjectInstance(MemoryUserDatabaseFactory.java:102)
at org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:94)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
at org.apache.naming.NamingContext.lookup(NamingContext.java:841)
at org.apache.naming.NamingContext.lookup(NamingContext.java:152)
at org.apache.naming.NamingContextBindingsEnumeration.nextElementInternal(NamingContextBindingsEnumeration.java:117)
at org.apache.naming.NamingContextBindingsEnumeration.next(NamingContextBindingsEnumeration.java:71)
at org.apache.naming.NamingContextBindingsEnumeration.next(NamingContextBindingsEnumeration.java:34)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.createMBeans(GlobalResourcesLifecycleListener.java:138)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.createMBeans(GlobalResourcesLifecycleListener.java:110)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.lifecycleEvent(GlobalResourcesLifecycleListener.java:82)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:394)
at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:339)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:780)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
21-Feb-2019 23:08:23.680 SEVERE [main] org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.createMBeans Exception processing Global JNDI Resources
javax.naming.NamingException: The markup in the document following the root element must be well-formed.
at org.apache.naming.NamingContext.lookup(NamingContext.java:858)
at org.apache.naming.NamingContext.lookup(NamingContext.java:152)
at org.apache.naming.NamingContextBindingsEnumeration.nextElementInternal(NamingContextBindingsEnumeration.java:117)
at org.apache.naming.NamingContextBindingsEnumeration.next(NamingContextBindingsEnumeration.java:71)
at org.apache.naming.NamingContextBindingsEnumeration.next(NamingContextBindingsEnumeration.java:34)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.createMBeans(GlobalResourcesLifecycleListener.java:138)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.createMBeans(GlobalResourcesLifecycleListener.java:110)
at org.apache.catalina.mbeans.GlobalResourcesLifecycleListener.lifecycleEvent(GlobalResourcesLifecycleListener.java:82)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:95)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:394)
at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:339)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:780)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
21-Feb-2019 23:08:23.681 INFO [main] org.apache.catalina.core.StandardService.startInternal Starting service Catalina
21-Feb-2019 23:08:23.681 INFO [main] org.apache.catalina.core.StandardEngine.startInternal Starting Servlet Engine: Apache Tomcat/8.0.36
21-Feb-2019 23:08:23.683 SEVERE [main] org.apache.tomcat.util.digester.Digester.fatalError Parse Fatal Error at line 46 column 2: The markup in the document following the root element must be well-formed.
org.xml.sax.SAXParseException; lineNumber: 46; columnNumber: 2; The markup in the document following the root element must be well-formed.
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:1472)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$TrailingMiscDriver.next(XMLDocumentScannerImpl.java:1395)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:602)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:505)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:841)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:770)
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:1470)
at org.apache.catalina.users.MemoryUserDatabase.open(MemoryUserDatabase.java:416)
at org.apache.catalina.users.MemoryUserDatabaseFactory.getObjectInstance(MemoryUserDatabaseFactory.java:102)
at org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:94)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
at org.apache.naming.NamingContext.lookup(NamingContext.java:841)
at org.apache.naming.NamingContext.lookup(NamingContext.java:166)
at org.apache.catalina.realm.UserDatabaseRealm.startInternal(UserDatabaseRealm.java:232)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.realm.CombinedRealm.startInternal(CombinedRealm.java:250)
at org.apache.catalina.realm.LockOutRealm.startInternal(LockOutRealm.java:120)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:903)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:441)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:787)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
21-Feb-2019 23:08:23.684 WARNING [main] org.apache.naming.NamingContext.lookup Unexpected exception resolving reference
org.xml.sax.SAXParseException; lineNumber: 46; columnNumber: 2; The markup in the document following the root element must be well-formed.
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1239)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)
at org.apache.tomcat.util.digester.Digester.parse(Digester.java:1470)
at org.apache.catalina.users.MemoryUserDatabase.open(MemoryUserDatabase.java:416)
at org.apache.catalina.users.MemoryUserDatabaseFactory.getObjectInstance(MemoryUserDatabaseFactory.java:102)
at org.apache.naming.factory.FactoryBase.getObjectInstance(FactoryBase.java:94)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
at org.apache.naming.NamingContext.lookup(NamingContext.java:841)
at org.apache.naming.NamingContext.lookup(NamingContext.java:166)
at org.apache.catalina.realm.UserDatabaseRealm.startInternal(UserDatabaseRealm.java:232)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.realm.CombinedRealm.startInternal(CombinedRealm.java:250)
at org.apache.catalina.realm.LockOutRealm.startInternal(LockOutRealm.java:120)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:903)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:441)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:787)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
21-Feb-2019 23:08:23.684 SEVERE [main] org.apache.catalina.realm.UserDatabaseRealm.startInternal Exception looking up UserDatabase under key UserDatabase
javax.naming.NamingException: The markup in the document following the root element must be well-formed.
at org.apache.naming.NamingContext.lookup(NamingContext.java:858)
at org.apache.naming.NamingContext.lookup(NamingContext.java:166)
at org.apache.catalina.realm.UserDatabaseRealm.startInternal(UserDatabaseRealm.java:232)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.realm.CombinedRealm.startInternal(CombinedRealm.java:250)
at org.apache.catalina.realm.LockOutRealm.startInternal(LockOutRealm.java:120)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:903)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:441)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:787)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
21-Feb-2019 23:08:23.685 SEVERE [main] org.apache.catalina.realm.CombinedRealm.startInternal Failed to start "org.apache.catalina.realm.UserDatabaseRealm" realm
org.apache.catalina.LifecycleException: Failed to start component [Realm[UserDatabaseRealm]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
at org.apache.catalina.realm.CombinedRealm.startInternal(CombinedRealm.java:250)
at org.apache.catalina.realm.LockOutRealm.startInternal(LockOutRealm.java:120)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:903)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:441)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:787)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)
Caused by: org.apache.catalina.LifecycleException: No UserDatabase component found under key UserDatabase
at org.apache.catalina.realm.UserDatabaseRealm.startInternal(UserDatabaseRealm.java:241)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
... 17 more问题分析：
从日志第一句话“org.apache.tomcat.util.digester.Digester.fatalError Parse Fatal Error at line 46 column 2: The markup in the document following the root element must be well-formed.” 可以看出，是tomcat中的某个配置文件没写对，但还无法知道是哪个配置文件，继续往下看错误信息“Caused by: org.apache.catalina.LifecycleException: No UserDatabase component found under key UserDatabase”，现在应该可以猜到了，应该是tomcat-user.xml，打开之后，发现之前加了一个用户，而且是加在“</tomcat-users>”的外面，出错位置也是错误信息里指出的第46行。修改好之后，重启tomcat服务器，搞定！
问题总结：
以后修改生产环境配置文件，除了做备份外，而且及时验证正确与否，如果不能做到及时验证配置文件，就不要提前修改，应和应用程序同步更新。