Eclipse：库问题

The type org.eclipse.jetty.http.HttpBuffers cannot be resolved. It is indirectly referenced from required .class files

import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.handler.HandlerList;
import org.eclipse.jetty.server.handler.ResourceHandler;
import org.eclipse.jetty.server.nio.SelectChannelConnector;
import org.eclipse.jetty.util.log.Log;


    public class FileServer {
        private FileServer() {
            Server server = new Server();
            SelectChannelConnector connector = new SelectChannelConnector();
            connector.setPort(8080);
            server.addConnector(connector); //Error this line
        }
    }

jetty-io-7.1.6.v20100715.jar   
jetty-security-7.1.6.v20100715.jar
jetty-server-7.1.6.v20100715.jar
jetty-servlet-7.1.6.v20100715.jar
jetty-util-7.1.6.v20100715.jar