Maven基础知识（2）

1.插件运行失败（这个找了很久，都是讲我的jdk和eclipse的jdk路径不一致，但是我的是一致的，结果重启了eclipse就可以了，很神奇，下次实在找不到参考可以先重启一下软件）

严重: Null component localEngine:type=JspMonitor,name=jsp,WebModule=//localhost/Maven-first,J2EEApplication=none,J2EEServer=none
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.555 s
[INFO] Finished at: 2018-04-04T14:29:29+08:00
[INFO] Final Memory: 14M/145M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:tomcat-maven-plugin:1.1:run (default-cli) on project Maven-first: Execution default-cli of goal org.codehaus.mojo:tomcat-maven-plugin:1.1:run failed. NullPointerException -> [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/PluginExecutionException

2.遇到这样的错误可能是软件包冲突，或者是JDK版本过高，或者是Tomcat服务器版本过低，从而导致冲突。解决方法更改高版本Tomcat或者降低JDK的版本。

严重: Compilation error
org.eclipse.jdt.internal.compiler.classfmt.ClassFormatException

3.为什么jar包的依赖范围设置为compile就会报错，设置为provided就不会报错？

严重: Exception starting filter struts2
java.lang.ClassCastException: org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter cannot be cast to javax.servlet.Filter

因为若是provided则项目会依赖tomcat带的jar包，否则项目中有jar包，tomcat也有，导致重复冲突，不知道使用谁的。
这里写图片描述