出现的问题：
严重: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Tomcat].StandardHost[localhost].StandardContext[]]
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1123)
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:800)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Tomcat].StandardHost[localhost].StandardContext[]]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:154)
... 6 more
Caused by: java.lang.ClassCastException: org.springframework.web.SpringServletContainerInitializer cannot be cast to javax.servlet.ServletContainerInitializer
at org.apache.catalina.startup.ContextConfig.getServletContainerInitializer(ContextConfig.java:1661)
at org.apache.catalina.startup.ContextConfig.processServletContainerInitializers(ContextConfig.java:1569)
at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1277)
at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:878)
at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:369)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5179)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
... 6 more
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.700 s
[INFO] Finished at: 2019-11-01T10:48:52+08:00
[INFO] Final Memory: 14M/162M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.tomcat.maven:tomcat7-maven-plugin:2.1:run (default-cli) on project SpringDay5Test2: Could not start Tomcat: Failed to start component [StandardServer[-1]]: Failed to start component [StandardService[Tomcat]]: Failed to start component [StandardEngine[Tomcat]]: A child container failed during start -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
Process finished with exit code 1
问题出现的原因及解决办法
原因：如果不加作用域，会造成依赖冲突，导致打包后有两套相同的jar包（javax.servlet-api和jsp-api）导致tomcat不知道用那一套。
解决：使用javax.servlet-api和jsp-api的时候没有配置作用范围
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope> <!--注意这里-->
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jsp-api</artifactId>
<version>2.0</version>
<scope>provided</scope> <!--注意这里-->
</dependency>
<scope>provided
</scope>
当为这两个插件配置作用域时，以上问题即可以解决。
