一个SpringCloud和SpringBoot版本搭配不对引发的异常(SpringBoot和SpringCloud版本搭配指南)

异常问题以及代码：SpringCloud项目启动报错： WebServerException: Unable to start embedded Tomcat

Caused by: org.springframework.boot.web.server.WebServerException: 
Unable to start embedded Tomcat at org.springframework.boot.web.embedded.tomcat.
TomcatWebServer.initialize(TomcatWebServer.java:142) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]

原因分析：

首先看SpringCloud项目的配置文件、父模块的pom.xml以及程序的启动类的注解配置，排除语法疏忽造成的bug后，就需要检查在pom.xml文件种对依赖的配置了。

• 原配置如下：我们可以看到SpringBoot的版本是2.3.0，而SpringCloud的版本则是Greenwich。经查证资料后发现，SpringCloud项目与SpringBoot有着比较严格的版本匹配。不能再像开发单体应用时，随时变更SpringBoot的版本。

    <!--引入SpringBoot环境-->
      <parent>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-parent</artifactId>
          <version>2.3.0.RELEASE</version>
          <relativePath/>
      </parent>
      <properties>        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
          <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
          <java.version>1.8</java.version>
          <!--spring cloud 版本-->
          <!--<spring-cloud.version>Hoxton.SR6</spring-cloud.version>-->
          <spring-cloud.version>Greenwich.RELEASE</spring-cloud.version>
      </properties>
  
      <!--引入Springcloud依赖-->
      <dependencyManagement>
          <dependencies>
              <dependency>
                  <groupId>org.springframework.cloud</groupId>
                  <artifactId>spring-cloud-dependencies</artifactId>
                  <version>${spring-cloud.version}</version>
                  <type>pom</type>
                  <scope>import</scope>
              </dependency>
          </dependencies>
      </dependencyManagement>

  故障解决：

  经过查找最新的SpringBoot和SpringCloud的版本对应关系，由于我们使用的SpringBoot是2.3.0，所以将SpringCloud的版本改为最新的正式版Hoxton.SR6即可。

  <properties>
          <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
          <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
          <java.version>1.8</java.version>
          <!--spring cloud 版本-->
          <spring-cloud.version>Hoxton.SR6</spring-cloud.version>
          <!-- <spring-cloud.version>Greenwich.RELEASE</spring-cloud.version>-->
  </properties>

  附：最新的SpringBoot和SpringCloud的版本对应关系查找，打开链接后返回的是个json数组，解析后即可。

  官方链接：start.spring.io/actuator/in…

  版本对应关系结果如下：

  "spring-cloud":{
  	"Finchley.M2":"Spring Boot >=2.0.0.M3 and <2.0.0.M5",
  	"Finchley.M3":"Spring Boot >=2.0.0.M5 and <=2.0.0.M5",
  	"Finchley.M4":"Spring Boot >=2.0.0.M6 and <=2.0.0.M6",
  	"Finchley.M5":"Spring Boot >=2.0.0.M7 and <=2.0.0.M7",
  	"Finchley.M6":"Spring Boot >=2.0.0.RC1 and <=2.0.0.RC1",
  	"Finchley.M7":"Spring Boot >=2.0.0.RC2 and <=2.0.0.RC2",
  	"Finchley.M9":"Spring Boot >=2.0.0.RELEASE and <=2.0.0.RELEASE",
  	"Finchley.RC1":"Spring Boot >=2.0.1.RELEASE and <2.0.2.RELEASE",
  	"Finchley.RC2":"Spring Boot >=2.0.2.RELEASE and <2.0.3.RELEASE",
  	"Finchley.SR4":"Spring Boot >=2.0.3.RELEASE and <2.0.999.BUILD-SNAPSHOT",
  	"Finchley.BUILD-SNAPSHOT":"Spring Boot >=2.0.999.BUILD-SNAPSHOT and <2.1.0.M3",
  	"Greenwich.M1":"Spring Boot >=2.1.0.M3 and <2.1.0.RELEASE",
  	"Greenwich.SR6":"Spring Boot >=2.1.0.RELEASE and <2.1.16.BUILD-SNAPSHOT",
  	"Greenwich.BUILD-SNAPSHOT":"Spring Boot >=2.1.16.BUILD-SNAPSHOT and <2.2.0.M4",
  	"Hoxton.SR6":"Spring Boot >=2.2.0.M4 and <2.3.2.BUILD-SNAPSHOT",
  	"Hoxton.BUILD-SNAPSHOT":"Spring Boot >=2.3.2.BUILD-SNAPSHOT and <2.4.0.M1",
  	"2020.0.0-SNAPSHOT":"Spring Boot >=2.4.0.M1"
  }