前段时间把rabbitMq系统过了一遍，由于没有demo演练，俗话说：“光看不练假把式”，于是乎便着手代码的实战。很久没接触普通spring工程项目了，这不刚集成rabbitMq，各种奇葩问题。好了，废话不多说，上演问题：

06-May-2020 17:25:40.085 严重 [RMI TCP Connection(4)-127.0.0.1] org.apache.catalina.core.StandardContext.listenerStart 配置应用程序监听器[org.springframework.web.context.ContextLoaderListener]错误
    java.lang.NoClassDefFoundError: javax/servlet/ServletContextListener
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2419)
        at org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:865)
        at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1334)
        at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1188)
        at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:541)
        at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:522)
        at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:151)
        at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4561)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5100)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:717)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:690)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:705)
        at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1728)
        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.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:289)
        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:456)
        at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:405)
        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.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:289)
        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:1468)
        at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76)
        at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1408)
        at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829)
        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 sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
        at sun.rmi.transport.Transport$1.run(Transport.java:200)
        at sun.rmi.transport.Transport$1.run(Transport.java:197)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:573)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:835)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:688)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:687)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
    Caused by: java.lang.ClassNotFoundException: javax.servlet.ServletContextListener
        at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1365)
        at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1188)
        ... 57 more

看到这个报错信息，很明显没找到ServletContextListener这个类，于是搜索官方的maven*仓库，复制粘贴

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
    <scope>provided</scope>
</dependency>

引入pom文件中，结果还是找不到，报同样的信息，再仔细看，sb了，<scope>provided</scope>以为着在编译和测试时候用，解决jar冲突问题，于是赶紧去掉，然而我笑了，接着开始报错：

06-May-2020 17:35:31.958 严重 [RMI TCP Connection(4)-127.0.0.1] org.apache.catalina.core.StandardContext.filterStart 启动过滤器异常
    java.lang.ClassCastException: org.springframework.web.filter.CharacterEncodingFilter cannot be cast to jakarta.servlet.Filter
        at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:250)
        at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:103)
        at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4487)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5126)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:717)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:690)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:705)
        at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1728)
        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.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:289)
        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:456)
        at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:405)
        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.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:289)
        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:1468)
        at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76)
        at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1408)
        at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829)
        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 sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
        at sun.rmi.transport.Transport$1.run(Transport.java:200)
        at sun.rmi.transport.Transport$1.run(Transport.java:197)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:573)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:835)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:688)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:687)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

继续查找原因，写个main方法测试程序所使用的filter所在jar路径是否正确：

public static void main(String[] args) {
        URL url = Filter.class.getProtectionDomain().getCodeSource().getLocation();
        System.out.println("path:"+url.getPath()+"  name:"+url.getFile());

    }

控制台输出：path:/E:/apache-maven-3.5.3/maven-repository/javax/servlet/javax.servlet-api/4.0.1/javax.servlet-api-4.0.1.jar  name:/E:/apache-maven-3.5.3/maven-repository/javax/servlet/javax.servlet-api/4.0.1/javax.servlet-api-4.0.1.jar

没毛病啊，就是我上面pom文件引入的jar所在的路径。于是查阅网上各种资料，说法比较多的解决思路是：idea中项目需要在Project Structure——》Modules——》Libary 引入tomcat中的类库，如下图：

 

然并卵，根源问题好像不在这。web启动时候，优先加载的是tomcat目录lib下的jar包，于是顺着这个思路去tomcat目录lib下查找sevele-api.jar，终于找到问题所在了，tomcat10和tomcat7、8版本

    

 

 果断替换低版本的tomcat，问题解决。同时，这也为我们提供了另一种思路，如果发生类似问题，找不到问题时先检查下是不是tomcat下和项目pom引入版本是否有冲突。对于上面idea中项目需要在Project Structure——》Modules——》Libary 引入tomcat中的类库这种解决问题的方案的前提姿势要对，即版本是匹配的，也是可以的。