Maven 在pom.xml中配置Jetty出现'org.eclipse.jetty.server.nio.SelectChannelConnector' cannot be loaded异常

<plugin>
<groupId>org.mortbay.jetty</groupId>
<artifactId>maven-jetty-plugin</artifactId>
<version>6.1.21</version>
<configuration>
<scanIntervalSeconds>10</scanIntervalSeconds>
<stopKey>foo</stopKey>
<stopPort>9999</stopPort>
<contextPath>/</contextPath>
<connectors>
<connector implementation="org.eclipse.jetty.server.nio.SelectChannelConnector">
<port>9090</port>
<maxIdleTime>60000</maxIdleTime>
</connector>
</connectors>
<webAppConfig>
<contextPath>/</contextPath>
</webAppConfig>
</configuration>
</plugin>

<connector implementation="org.eclipse.jetty.server.nio.SelectChannelConnector">

<connector implementation="org.mortbay.jetty.nio.SelectChannelConnector">