報錯信息如下：

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.snts.eureka.server.EurekaServerApplication.main(EurekaServerApplication.java:12) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_192]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_192]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_192]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_192]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.2.0.RELEASE.jar:2.2.0.RELEASE]
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.<init>(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]
    ... 13 common frames omitted
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: 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)}
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:787) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:528) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1338) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:557) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:207) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.getOrderedBeansOfType(ServletContextInitializerBeans.java:211) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.getOrderedBeansOfType(ServletContextInitializerBeans.java:202) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.addServletContextInitializerBeans(ServletContextInitializerBeans.java:96) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.<init>(ServletContextInitializerBeans.java:85) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.getServletContextInitializerBeans(ServletWebServerApplicationContext.java:253) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.selfInitialize(ServletWebServerApplicationContext.java:227) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    at org.springframework.boot.web.embedded.tomcat.TomcatStarter.onStartup(TomcatStarter.java:53) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5135) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1384) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1374) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[na:1.8.0_192]
    at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134) ~[na:1.8.0_192]
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:909) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:841) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1384) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1374) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[na:1.8.0_192]
    at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134) ~[na:1.8.0_192]
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:909) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:421) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:930) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.startup.Tomcat.start(Tomcat.java:459) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.initialize(TomcatWebServer.java:107) ~[spring-boot-2.2.0.RELEASE.jar:2.2.0.RELEASE]
    ... 18 common frames omitted
Caused by: 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)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1695) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1253) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1207) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:874) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:778) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE]
    ... 58 common frames omitted

剛開始遇到這個問題的時候很懵，從報錯信息來看很難看出來具體什麼問題，我一直以爲是spring-web包的問題，解決了半天，經過一番關鍵字查找，發現spring cloud 與spring boot有着比較嚴格的版本匹配。不能再像開發單體應用時，隨時變更spring boot的版本。

我這裏使用的spring版本是：

 <parent>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-parent</artifactId>
     <version>2.1.4.RELEASE</version>
     <relativePath/> <!-- lookup parent from repository -->
 </parent>

經過修改後的Eureka版本：

<dependencyManagement>
    <dependencies>
         <dependency>
             <groupId>org.springframework.cloud</groupId>
             <artifactId>spring-cloud-dependencies</artifactId>
             <version>Greenwich.SR1</version>
             <type>pom</type>
             <scope>import</scope>
         </dependency>
     </dependencies>
</dependencyManagement>

問題順利解決。

現將版本對應規則寫下來，引用的是其他網友的博客。

來源：https://www.cnblogs.com/it-taosir/p/9979579.html

一、常見版本號說明

　　舉個瓜：2.0.3 RELEASE

　　2：主版本號，當功能模塊有較大更新或者整體架構發生變化時，主版本號會更新

　　0：次版本號。次版本表示只是局部的一些變動。

　　2：修改版本號。一般是bug的修改或者是小的變動

　　RELEASE：希臘字母版本號。此版本號用戶標註當前版本的軟件處於哪個開發階段

 

二、希臘字母版本號

　　Base：設計階段。只有相應的設計沒有具體的功能實現。

　　Alpha：軟件的初級版本。基本功能已經實現，但存在較多的bug。

　　Bate：相對於Alpha已經有了很大的進步，消除了嚴重的BUG，但還存在一些潛在的BUG，還需要不斷測試。

　　RELEASE：最終版本，沒有太大的問題。

 

三、SpringCloud的版本號

　　1）爲什麼springcloud版本用的是單詞而不是數字呢？

　　　　設計的目的是爲了更好的管理每個SpringCloud子項目的清單，避免自己的版本號與子項目的版本號混淆。

　　2）有什麼規則麼？

　　　　（常用了英國倫敦地鐵站的名稱來命名）首字母越靠後表示版本號越大

　　3）關於版本發佈說明？

　　　　BUILD-XXX　　　　　　開發版　　　　開發團隊內部使用，不是很穩定

　　　　GA　　　　　　　　　　穩定版　　　　相比於開發版，基本上可以使用了

　　　　PRE（M1、M2）　　　  里程碑版　　　主要是修復了一些BUG的版本，一個GA後通常有多個里程碑版

　　　　RC　　　　　　　　　　候選發佈版　　該階段的軟件類似於最終版的一個發行觀察期，基本只修復比較嚴重的BUG

　　　　SR　　　　　　　　　　正式發佈版　　~~~~這個就沒啥好說啦

Eureka配置報錯Unable to start web server;

報錯信息如下：

我這裏使用的spring版本是：

經過修改後的Eureka版本：

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Eureka配置報錯Unable to start web server;

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