pom.xml文件的头部<project>标签提示错误：

Failure to transfer org.apache.maven.plugins:maven-jar-plugin:pom:2.6 from http://maven.aliyun.com/nexus/content/groups/public/ was  cached in the local repository, resolution will not be reattempted until the update interval of alimaven has elapsed or updates are forced.  Original error: Could not transfer artifact org.apache.maven.plugins:maven-jar-plugin:pom:2.6 from/to alimaven (http://maven.aliyun.com/ nexus/content/groups/public/): The operation was cancelled.

解决方案：查看user settings中配置的仓库地址（为.m2），改成自己正在用的本地仓库。再maven  -->update一下项目