前言
SpringBoot默认使用的使用的是嵌入式的Servlet容器。当我们使用外部的Servlet容器时，会遇到各种各样的问题。
使用的环境: IDEA + apache-tomcat-7.0.91
1.springboot启动tomcat报错java.lang.NoClassDefFoundError: javax/el/ELManager
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.validation.beanvalidation.LocalValidatorFactoryBean]: Factory method 'defaultValidator' threw exception; nested exception is java.lang.NoClassDefFoundError: javax/el/ELManager
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185)
at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1468) [na:1.8.0_121]
at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76) [na:1.8.0_121]
at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309) [na:1.8.0_121]
at java.security.AccessController.doPrivileged(Native Method) [na:1.8.0_121]
at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1408) [na:1.8.0_121]
at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829) [na:1.8.0_121]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_121]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_121]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_121]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_121]
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:346) [na:1.8.0_121]
at sun.rmi.transport.Transport$1.run(Transport.java:200) [na:1.8.0_121]
at sun.rmi.transport.Transport$1.run(Transport.java:197) [na:1.8.0_121]
at java.security.AccessController.doPrivileged(Native Method) [na:1.8.0_121]
at sun.rmi.transport.Transport.serviceCall(Transport.java:196) [na:1.8.0_121]
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568) [na:1.8.0_121]
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826) [na:1.8.0_121]
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683) [na:1.8.0_121]
at java.security.AccessController.doPrivileged(Native Method) [na:1.8.0_121]
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) ~[na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) ~[na:1.8.0_121]
at java.lang.Thread.run(Thread.java:745) ~[na:1.8.0_121]
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.validation.beanvalidation.LocalValidatorFactoryBean]: Factory method 'defaultValidator' threw exception; nested exception is java.lang.NoClassDefFoundError: javax/el/ELManager
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:651) ~[spring-beans-5.2.3.RELEASE.jar:5.2.3.RELEASE]
... 66 common frames omitted
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:651)
... 66 more
Caused by: java.lang.NoClassDefFoundError: javax/el/ELManager
at org.hibernate.validator.messageinterpolation.ResourceBundleMessageInterpolator.buildExpressionFactory(ResourceBundleMessageInterpolator.java:88)
at org.hibernate.validator.messageinterpolation.ResourceBundleMessageInterpolator.<init>(ResourceBundleMessageInterpolator.java:47)
at org.hibernate.validator.internal.engine.ConfigurationImpl.getDefaultMessageInterpolator(ConfigurationImpl.java:474)
at org.springframework.boot.validation.MessageInterpolatorFactory.getObject(MessageInterpolatorFactory.java:53)
at org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration.defaultValidator(ValidationAutoConfiguration.java:57)
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.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
... 67 more
解析：
报错的内容非常多，但关键在于Caused by: java.lang.NoClassDefFoundError: javax/el/ELManager，这个问题百度了许久，有所把IDEA中的el-api拷贝到tomcat，有修改tomcat下的catalina.properties文件的，发现由于IDEA的版本比较高（tomcat的版本也比较高，所以根本没有el-api文件），修改了配置文件也依然报错。
在网上又百度了许久，才知反编译el-api的确没有ElManager，在el-api3.0才引入（因为我们用的tomcat版本过低），我们可以直接下载
javax.el-api-3.0-b07.jar，放到我们tomcat/lib下即可(还有一种就是使用tomcat8即可)
2.SpringBoot启动jsp页面报错java.lang.NoSuchMethodError: javax.el.ExpressionFactory.newInstance()Ljavax/el/ExpressionFactory
javax.servlet.ServletException: java.lang.NoSuchMethodError: javax.el.ExpressionFactory.newInstance()Ljavax/el/ExpressionFactory;
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:348) ~[jasper.jar:7.0.91]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731) ~[servlet-api.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) [catalina.jar:7.0.91]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [catalina.jar:7.0.91]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat7-websocket.jar:7.0.91]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [catalina.jar:7.0.91]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [catalina.jar:7.0.91]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) [spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [catalina.jar:7.0.91]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [catalina.jar:7.0.91]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) [spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [catalina.jar:7.0.91]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [catalina.jar:7.0.91]
at org.springframework.boot.web.servlet.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:128) [spring-boot-2.2.4.RELEASE.jar:2.2.4.RELEASE]
at org.springframework.boot.web.servlet.support.ErrorPageFilter.access$000(ErrorPageFilter.java:66) [spring-boot-2.2.4.RELEASE.jar:2.2.4.RELEASE]
at org.springframework.boot.web.servlet.support.ErrorPageFilter$1.doFilterInternal(ErrorPageFilter.java:103) [spring-boot-2.2.4.RELEASE.jar:2.2.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) [spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.springframework.boot.web.servlet.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:121) [spring-boot-2.2.4.RELEASE.jar:2.2.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [catalina.jar:7.0.91]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [catalina.jar:7.0.91]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) [spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) [spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [catalina.jar:7.0.91]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [catalina.jar:7.0.91]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) [catalina.jar:7.0.91]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110) [catalina.jar:7.0.91]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:494) [catalina.jar:7.0.91]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169) [catalina.jar:7.0.91]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104) [catalina.jar:7.0.91]
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:1025) [catalina.jar:7.0.91]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) [catalina.jar:7.0.91]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445) [catalina.jar:7.0.91]
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1137) [tomcat-coyote.jar:7.0.91]
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637) [tomcat-coyote.jar:7.0.91]
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2555) [tomcat-coyote.jar:7.0.91]
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2544) [tomcat-coyote.jar:7.0.91]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-coyote.jar:7.0.91]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]
Caused by: java.lang.NoSuchMethodError: javax.el.ExpressionFactory.newInstance()Ljavax/el/ExpressionFactory;
at org.apache.jasper.compiler.PageInfo.<init>(PageInfo.java:79) ~[jasper.jar:7.0.91]
at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:111) ~[jasper.jar:7.0.91]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:374) ~[jasper.jar:7.0.91]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:354) ~[jasper.jar:7.0.91]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:341) ~[jasper.jar:7.0.91]
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:660) ~[jasper.jar:7.0.91]
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:378) ~[jasper.jar:7.0.91]
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395) ~[jasper.jar:7.0.91]
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339) ~[jasper.jar:7.0.91]
... 41 common frames omitted
解析：
到网上又是一顿折腾，原来又是缺少com.sun.el.ExpressionFactoryImpl这个类，所以没有他相应的方法，接着又发现了几个与它相关的jar包。
解决方法: 将juel.jar, juel-engine.jar, juel-impl.jar放到我们tomcat的lib目录下
以上4个jar包都可以通过https://www.mvnjar.com/进行下载
总结:
SpringBoot使用外部Servlet容器的tomcat时，尽量使用8.0以上的版本，否则你会发现各种各样的jar包会缺少。
