SpringBoot系列(二)指定内置tomcat版本

简言
SpringBoot内置的tomcat版本是随着SpringBoot版本走的，比如我这SpringBoot 版本是1.5.9，内置tomcat版本是8.5.23；假如需要修改内置的tomcat版本号，则在POM依赖里< properties >里添加< tomcat.version>8.0.42< /tomcat.version>

注意：我上面标签是有空格的；

<properties>
    <tomcat.version>8.0.42tomcat.version>
properties>

指定完tomcat版本后可以查看maven 依赖树，查看内置tomcat版本是否变为指定版本，重启项目，但是有时候启动会报错：

Tomcat启动报错代码 ：

Caused by: java.lang.NoClassDefFoundError: org/apache/juli/logging/LogFactory 
  at org.apache.catalina.util.LifecycleBase.(LifecycleBase.java:37) 
  at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory.getEmbeddedServletContainer(TomcatEmbeddedServletContainerFactory.java:169) 
  at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.createEmbeddedServletContainer(EmbeddedWebApplicationContext.java:164) 
  at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh(EmbeddedWebApplicationContext.java:134) 
  ... 13 common frames omitted 

因为这个时候的tocmat缺少jar包，maven项目的话加上下面这个依赖就好了：

<dependency> 
   <groupId>org.apache.tomcatgroupId> 
   <artifactId>tomcat-juliartifactId> 
   <version>${tomcat.version}version> 
 dependency>

修改完后，能在控制台启动日志里看到tomcat的启动版本：

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.9.RELEASE)

2018-03-09 11:01:58.104  INFO 5036 --- [           main] com.jd.m.tg.MTgApplication               : The following profiles are active: dev
2018-03-09 11:01:58.218  INFO 5036 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@9bfddc: startup date [Fri Mar 09 11:01:58 CST 2018]; root of context hierarchy
2018-03-09 11:01:58.546  INFO 5036 --- [kground-preinit] o.h.validator.internal.util.Version      : HV000001: Hibernate Validator 5.3.6.Final
2018-03-09 11:02:01.176  INFO 5036 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 80 (http)
2018-03-09 11:02:01.188  INFO 5036 --- [           main] o.apache.catalina.core.StandardService   : Starting service Tomcat
2018-03-09 11:02:01.190  INFO 5036 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.0.42