"Unable to start embedded Tomcat" 问题

报错堆栈日志

2019-11-05 14:43:34.593 ERROR 4536 --- [           main] o.s.b.web.embedded.tomcat.TomcatStarter  : Error starting Tomcat context. Exception: org.springframework.beans.factory.UnsatisfiedDependencyException. Message: Error creating bean with name 'traceFilterRegistration' defined in class path resource [org/springframework/cloud/netflix/eureka/server/EurekaServerAutoConfiguration.class]: Unsatisfied dependency expressed through method 'traceFilterRegistration' parameter 0; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'javax.servlet.Filter' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Qualifier(value=httpTraceFilter)}
2019-11-05 14:43:34.623  INFO 4536 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
2019-11-05 14:43:34.628  WARN 4536 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat
2019-11-05 14:43:34.640  INFO 4536 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2019-11-05 14:43:34.798 ERROR 4536 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:156) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:544) ~[spring-context-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) [spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at com.deepflow.eurekaserver.EurekaServerApplication.main(EurekaServerApplication.java:12) [classes/:na]
Caused by: org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat
	at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.initialize(TomcatWebServer.java:126) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.(TomcatWebServer.java:88) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getTomcatWebServer(TomcatServletWebServerFactory.java:438) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getWebServer(TomcatServletWebServerFactory.java:191) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:180) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:153) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	... 8 common frames omitted

分析原因

网上说了很多解决办法, 有的是手动配置配置一个外置的Tomcat, 有的说是jar包冲突. 仔细想想应该都没有把握核心, Springboot已经集成了内置的Tomcat, 所以没有必要再配置一个外置的Tomcat.
错误日志有一句信息很重要:

2019-11-05 14:43:34.593 ERROR 4536 --- [           main] o.s.b.web.embedded.tomcat.TomcatStarter  : Error starting Tomcat context. Exception: org.springframework.beans.factory.UnsatisfiedDependencyException. Message: Error creating bean with name 'traceFilterRegistration' defined in class path resource [org/springframework/cloud/netflix/eureka/server/EurekaServerAutoConfiguration.class]: Unsatisfied dependency expressed through method 'traceFilterRegistration' parameter 0; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'javax.servlet.Filter' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Qualifier(value=httpTraceFilter)}

这句日志表明, Tomcat已经被引入进来了, 只是“traceFilterRegistration” 这个方法缺少一个参数, 导致Tomcat无法被加载进来.
由此可以想到有可能是Springcloud版本和Springboot版本不一致所导致的, 查看pom文件一看果然如此:

    
        org.springframework.boot
        spring-boot-starter-parent
        2.2.0.RELEASE
         
    
    
        1.8
        Finchley.RELEASE
    
    
        
            org.springframework.cloud
            spring-cloud-dependencies
            ${spring-cloud.version}
            pom
            import
        
    

Springcloud的版本是Finchley.RELEASE, 这个版本对应的Springboot是: 2.0.0.RELEASE~2.0.9.RELEASE.换句话说就是低版本的cloud配了高版本的boot. boot版本往下降到2.0.x即可:

    
        org.springframework.boot
        spring-boot-starter-parent
        2.0.9.RELEASE
         
    
    
        1.8
        Finchley.RELEASE
    
    
        
            org.springframework.cloud
            spring-cloud-dependencies
            ${spring-cloud.version}
            pom
            import
        
    

延伸

Springcloud版本和Springboot版本对应关系:https://blog.csdn.net/zjhcxdj/article/details/102917380