[INFO] The plugin 'org.apache.maven.plugins:maven-jetty-plugin' does  not exist or no valid version could be found conf/setting.xml里面：  <!-- pluginGroups   | This is a list of additional group identifiers that will be searched when resolving plugins by their prefix, i.e.   | when invoking a command line like "mvn prefix:goal". Maven will automatically add the group identifiers   | "org.apache.maven.plugins" and "org.codehaus.mojo" if these are not already contained in the list.   |-->  <pluginGroups>   <pluginGroup>org.mortbay.jetty</pluginGroup>    <!-- pluginGroup     | Specifies a further group identifier to use for plugin lookup.    <pluginGroup>com.your.plugins</pluginGroup>    -->  </pluginGroups>