- [ ] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [ ] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.3
* Operating System version: macOs sierra
* Java version: 1.8

### Steps to reproduce this issue

Sometimes, when debugging connect time issue, we don't know whether the port is listening.  We can check the connected log if the connect timeout occurs.
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.dubbo.remoting.transport.netty;
import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.utils.NetUtils;
import org.apache.dubbo.remoting.Channel;
import org.apache.dubbo.remoting.ChannelHandler;
import org.jboss.netty.channel.ChannelHandler.Sharable;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelStateEvent;
import org.jboss.netty.channel.ExceptionEvent;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.channel.SimpleChannelHandler;
import java.net.InetSocketAddress;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
/**
 * NettyHandler
 */
@Sharable
public class NettyHandler extends SimpleChannelHandler {
    private final Map<String, Channel> channels = new ConcurrentHashMap<String, Channel>(); 
    private final URL url;
    private final ChannelHandler handler;
    public NettyHandler(URL url, ChannelHandler handler) {
        if (url == null) {
            throw new IllegalArgumentException("url == null");
        }