[ERROR] Failed to execute goal org.mortbay.jetty:jetty-maven-plugin:8.1.16.v20140903:run (default-cli) on project demo: Execution default-cli of goal org.mortbay.jetty:jetty-maven-plugin:8.1.16.v20140903:run failed: Plugin org.mortbay.jetty:jetty-maven-plugin:8.1.16.v20140903 or one of its dependencies could not be resolved: The following artifacts could not be resolved: org.eclipse.jetty:jetty-util:jar:8.1.16.v20140903, org.eclipse.jetty:jetty-webapp:jar:8.1.16.v20140903, org.apache.maven.plugin-tools:maven-plugin-tools-api:jar:2.9, org.eclipse.jetty:jetty-plus:jar:8.1.16.v20140903, org.eclipse.jetty:jetty-jndi:jar:8.1.16.v20140903, org.eclipse.jetty:jetty-jmx:jar:8.1.16.v20140903, org.eclipse.jetty:jetty-annotations:jar:8.1.16.v20140903, org.eclipse.jetty:jetty-websocket:jar:8.1.16.v20140903, org.eclipse.jetty:jetty-jsp:jar:8.1.16.v20140903, org.codehaus.plexus:plexus-utils:jar:1.1: Cannot access central (https://repo.maven.apache.org/maven2) in offline mode and the artifact org.eclipse.jetty:jetty-util:jar:8.1.16.v20140903 has not been downloaded from it before. -> [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
org.eclipse.jetty:jetty-util:jar:8.1.16.v20140903
可能是上面这个jar包自动下载失败，你可以手动下载下来放到.m2文件夹下的相应路径里
你看看你的电脑里是不是有一个jetty正在运行