一、exception描述：
1、jdk版本8，tomcat版本8，maven版本3.3.3
2、在svn中导出的工程，工程本身并没有问题，其他同事都能够运行，
3、怀疑是maven版本问题，在之前的工作电脑上的maven是3.2.3，换了电脑之后maven是3.3.3，运行项 目就出错了，但是不知道具体原因。
二、exception栈中的错误信息
[ERROR] Failed to execute goal org.apache.tomcat.maven:tomcat7-
maven-plugin:2.1:run (default-cli) on project projectName:
Execution default-cli of goal org.apache.tomcat.maven:tomcat7-maven-plugin:2.1:run
failed: Plugin org.apache.tomcat.maven:tomcat7-maven-
plugin:2.1 or one of its dependencies could not be resolved:
Could not transfer artifact org.apache.tomcat.embed:tomcat-
embed-core:jar:7.0.37 from/to central
(https://repo.maven.apache.org/maven2): Connect to repo.maven.apache.org:443
[repo.maven.apache.org/23.235.47.215]failed: Connection timed out:connect->[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/PluginResolutionException
三、后来在网上找了很多文章，并没有和这个一样的错误，我就总是执行maven那几个常用命令，莫名其妙的好了。。。。。到现在还是不知道这是为什么。。。。。。。