具体错误日志：
org.apache.catalina.LifecycleException: Protocol handler start failed
     at org.apache.catalina.connector.Connector.startInternal(Connector.java:1008) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
     at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
     at org.apache.catalina.core.StandardService.addConnector(StandardService.java:226) ~[tomcat-embed-core-9.0.16.jar:9.0.16]
     at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.addPreviouslyRemovedConnectors(TomcatWebServer.java:259) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.start(TomcatWebServer.java:197) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.startWebServer(ServletWebServerApplicationContext.java:311) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.finishRefresh(ServletWebServerApplicationContext.java:164) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:552) ~[spring-context-5.1.5.RELEASE.jar:5.1.5.RELEASE]
     at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) ~[spring-boot-2.1.3.RELEASE.jar:2.1.3.RELEASE]
     at cn.changemax.springbootdemo.SpringbootDemoApplication.main(SpringbootDemoApplication.java:11) ~[classes/:na] 
 
其实错误产生原因很简单，就是端口号冲突了，原因是我启动了两个端口为8080的应用。
 
解决方式：1.要么检查一下本地主机是否哪里还启动了springboot的中的tomcat服务器应用，2.要么就改一下端口号为：8081、8082