首先废话不多说，可能你没有错，错的是 Idea。。。
建议 ：
换成 eclipse 或者 STS 试一试。
我本机环境：
spring boot 2.6.3
Idea版本 2018.2
$ java -version java version "1.8.0_201" Java(TM) SE Runtime Environment (build 1.8.0_201-b09) Java HotSpot(TM) 64-Bit Server VM (build 25.201-b09, mixed mode) $ mvn -version Apache Maven 3.6.12. 问题
理论上是在有 forward 请求时候，就会出现错误，比如springboot的欢迎页，他会报错：
# 访问会报错 localhost:8080/
WelcomePageHandlerMapping(TemplateAvailabilityProviders templateAvailabilityProviders,
ApplicationContext applicationContext, Resource welcomePage, String staticPathPattern) {
if (welcomePage != null && "/**".equals(staticPathPattern)) {
logger.info("Adding welcome page: " + welcomePage);
setRootViewName("forward:index.html");
}
else if (welcomeTemplateExists(templateAvailabilityProviders, applicationContext)) {
logger.info("Adding welcome page template: index");
setRootViewName("index");
}
}
找了半天，网上有说，tomcat版本问题的，结果idea里面改了版本，直接启动就报错，我的idea2018.2里面最低只有 2.5.9；
雷神视频里面用的，是springboot2.3.4；
关于版本问题，可以在官网里面看，实际上，版本应该没问题。
。。。。。
结果是，我突发奇想，用sts重新建了一个一样的项目，重新访问 localhost:8080，他就行了。具体原因不明白，应该是 Idea 的问题。。。
RequestAttribute 的例子也OK了，之前用Idea 死活是 500 。。。
关键的句子：
Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler processing failed; nested exception is java.lang.NoSuchMethodError: javax.servlet.http.HttpServletRequest.getHttpServletMapping()Ljavax/servlet/http/HttpServletMapping;] with root cause
java.lang.NoSuchMethodError: javax.servlet.http.HttpServletRequest.getHttpServletMapping()Ljavax/servlet/http/HttpServletMapping;
ERROR 23248 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost] : Exception Processing ErrorPage[errorCode=0, location=/error]
2022-02-02 12:02:50.047 ERROR 23248 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler processing failed; nested exception is java.lang.NoSuchMethodError: javax.servlet.http.HttpServletRequest.getHttpServletMapping()Ljavax/servlet/http/HttpServletMapping;] with root cause java.lang.NoSuchMethodError: javax.servlet.http.HttpServletRequest.getHttpServletMapping()Ljavax/servlet/http/HttpServletMapping; at org.apache.catalina.core.ApplicationHttpRequest.setRequest(ApplicationHttpRequest.java:714) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationHttpRequest.(ApplicationHttpRequest.java:113) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationDispatcher.wrapRequest(ApplicationDispatcher.java:920) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:359) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:313) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:171) ~[spring-webmvc-5.3.15.jar:5.3.15] at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:316) ~[spring-webmvc-5.3.15.jar:5.3.15] at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1401) ~[spring-webmvc-5.3.15.jar:5.3.15] at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1145) ~[spring-webmvc-5.3.15.jar:5.3.15] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1084) ~[spring-webmvc-5.3.15.jar:5.3.15] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.15.jar:5.3.15] at org.springframework.web.servlet.frameworkServlet.processRequest(frameworkServlet.java:1006) ~[spring-webmvc-5.3.15.jar:5.3.15] at org.springframework.web.servlet.frameworkServlet.doGet(frameworkServlet.java:898) ~[spring-webmvc-5.3.15.jar:5.3.15] at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) ~[servlet-api.jar:na] at org.springframework.web.servlet.frameworkServlet.service(frameworkServlet.java:883) ~[spring-webmvc-5.3.15.jar:5.3.15] at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[servlet-api.jar:na] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.15.jar:5.3.15] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.15.jar:5.3.15] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.15.jar:5.3.15] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.15.jar:5.3.15] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.15.jar:5.3.15] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.15.jar:5.3.15] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.authenticator.Authenticatorbase.invoke(Authenticatorbase.java:540) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardEnginevalve.invoke(StandardEnginevalve.java:78) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:895) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1732) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.net.SocketProcessorbase.run(SocketProcessorbase.java:49) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.56.jar:9.0.56] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201] 2022-02-02 12:02:50.053 ERROR 23248 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost] : Exception Processing ErrorPage[errorCode=0, location=/error] java.lang.NoSuchMethodError: javax.servlet.http.HttpServletRequest.getHttpServletMapping()Ljavax/servlet/http/HttpServletMapping; at org.apache.catalina.core.ApplicationHttpRequest.setRequest(ApplicationHttpRequest.java:714) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationHttpRequest. (ApplicationHttpRequest.java:113) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationDispatcher.wrapRequest(ApplicationDispatcher.java:920) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:359) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:313) ~[tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:403) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:249) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:344) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.core.StandardEnginevalve.invoke(StandardEnginevalve.java:78) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:895) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1732) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.net.SocketProcessorbase.run(SocketProcessorbase.java:49) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.56.jar:9.0.56] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.56.jar:9.0.56] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201]
祝大家新年快乐！
希望2022，我能技术进步，收获那个，，爱情，哈哈哈哈哈
