2019-10-17 11:36:33.845 INFO 12916 --- [ main] com.yzx.demo.DemoApplication : Starting DemoApplication on DESKTOP-0PUN91C with PID 12916 (C:\workspace\demo\target\classes started by Lyand in C:\workspace\demo)
2019-10-17 11:36:33.849 INFO 12916 --- [ main] com.yzx.demo.DemoApplication : No active profile set, falling back to default profiles: default
2019-10-17 11:36:34.973 INFO 12916 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2019-10-17 11:36:34.999 INFO 12916 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2019-10-17 11:36:34.999 INFO 12916 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.26]
2019-10-17 11:36:35.097 INFO 12916 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2019-10-17 11:36:35.097 INFO 12916 --- [ main] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1190 ms
2019-10-17 11:36:35.289 INFO 12916 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor'
2019-10-17 11:36:35.458 INFO 12916 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2019-10-17 11:36:35.461 INFO 12916 --- [ main] com.yzx.demo.DemoApplication : Started DemoApplication in 1.957 seconds (JVM running for 2.337)
2019-10-17 11:36:56.504 INFO 12916 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2019-10-17 11:36:56.505 INFO 12916 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2019-10-17 11:36:56.511 INFO 12916 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 6 ms
尝试，解决办法：
， com.yzx.controller.demo，一定要在com.yzx.controller下边
源地址
https://blog.csdn.net/fyhailin/article/details/78476992