项目报错日志：
严重: Containerbase.addChild: start:
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/HelloS]]
at org.apache.catalina.util.Lifecyclebase.start(Lifecyclebase.java:154)
at org.apache.catalina.core.Containerbase.addChildInternal(Containerbase.java:901)
at org.apache.catalina.core.Containerbase.addChild(Containerbase.java:877)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:649)
at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1760)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.tomcat.util.modeler.baseModelMBean.invoke(baseModelMBean.java:301)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:618)
at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:565)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.tomcat.util.modeler.baseModelMBean.invoke(baseModelMBean.java:301)
at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
at com.sun.jmx.remote.security.MBeanServerAccessController.invoke(MBeanServerAccessController.java:468)
at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1487)
at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:97)
at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1328)
at java.security.AccessController.doPrivileged(Native Method)
at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1427)
at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:848)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:322)
at sun.rmi.transport.Transport$1.run(Transport.java:177)
at sun.rmi.transport.Transport$1.run(Transport.java:174)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:556)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:811)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:670)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.UnsupportedClassVersionError: org/springframework/web/SpringServletContainerInitializer : Unsupported major.minor version 52.0 (unable to load class org.springframework.web.SpringServletContainerInitializer)
at org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:2961)
at org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:1210)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1690)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:270)
at org.apache.catalina.startup.WebappServiceLoader.loadServices(WebappServiceLoader.java:187)
at org.apache.catalina.startup.WebappServiceLoader.load(WebappServiceLoader.java:152)
at org.apache.catalina.startup.ContextConfig.processServletContainerInitializers(ContextConfig.java:1559)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1281)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:889)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:386)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
at org.apache.catalina.util.Lifecyclebase.fireLifecycleEvent(Lifecyclebase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5380)
at org.apache.catalina.util.Lifecyclebase.start(Lifecyclebase.java:150)
... 42 more
折腾了半天，网上查找了资料，一直没能解决，后来发现是版本的问题
刚接触idea，下载了2020.3的版本，创建的web版本是5.0，创建项目的时候不能修改降低版本，而jdk配置的1.7，tomcat用的7，所以就报这个错误了。后来将jdk改为1.8，tomcat改成9正常启动。
而后又继续复现问题，留作记录，发现只是jdk的影响，jdk1.8配tomcat7也能正常启动项目。
干的久了就有恋旧的情节，jdk1.7一直用到现在，懒得更换，所以就忽略了版本的问题。
