解决办法：
1.项目右键Properties
2.搜索Deployment Assembly
3.点击add
4.选择Java Build Path Entries
5.点击next 选择Maven Dependencies 点击Finish
6.点击Apply and Close
创建一个maven项目时启动项目控制台抛出了错误信息：
严重: Error configuring application listener of class org.springframework.web.context.ContextLoaderListener java.lang.ClassNotFoundException: org.springframework.web.context.ContextLoaderListener at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1333) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1167) at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:509) at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:490) at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:118) at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4775) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5314) 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$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) 十二月 05, 2020 2:05:36 下午 org.apache.catalina.core.StandardContext listenerStart 严重: Error configuring application listener of class org.springframework.web.util.IntrospectorCleanupListener java.lang.ClassNotFoundException: org.springframework.web.util.IntrospectorCleanupListener at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1333) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1167) at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:509) at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:490) at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:118) at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4775) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5314) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145) at org.apache.catalina.core.ContainerBase$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 05, 2020 2:05:36 下午 org.apache.catalina.core.StandardContext listenerStart 严重: Skipped installing application listeners due to previous error(s) 十二月 05, 2020 2:05:36 下午 org.apache.catalina.core.StandardContext startInternal 严重: One or more listeners failed to start. Full details will be found in the appropriate container log file 十二月 05, 2020 2:05:36 下午 org.apache.catalina.core.StandardContext startInternal 严重: Context [/MyDemo] startup failed due to previous errors 十二月 05, 2020 2:05:36 下午 org.apache.coyote.AbstractProtocol start 信息: Starting ProtocolHandler ["http-nio-8080"] 十二月 05, 2020 2:05:36 下午 org.apache.coyote.AbstractProtocol start 信息: Starting ProtocolHandler ["ajp-nio-8009"] 十二月 05, 2020 2:05:36 下午 org.apache.catalina.startup.Catalina start 信息: Server startup in 733 ms
但是发现maven的依赖包都是下载了的，于是又找其他的问题。