public class ProtocolListenerWrapper implements Protocol {

  private final Protocol protocol;

  public ProtocolListenerWrapper(Protocol protocol){
    if (protocol == null) {
      throw new IllegalArgumentException("protocol == null");
    }
    this.protocol = protocol;
  }

  public int getDefaultPort() {
    return protocol.getDefaultPort();
  }

  public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
    if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
      return protocol.export(invoker);
    }
    return new ListenerExporterWrapper<T>(protocol.export(invoker),
        Collections.unmodifiableList(ExtensionLoader.getExtensionLoader(ExporterListener.class)
            .getActivateExtension(invoker.getUrl(), Constants.EXPORTER_LISTENER_KEY)));
  }

  public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
    if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
      return protocol.refer(type, url);
    }
    return new ListenerInvokerWrapper<T>(protocol.refer(type, url),
        Collections.unmodifiableList(
            ExtensionLoader.getExtensionLoader(InvokerListener.class)
            .getActivateExtension(url, Constants.INVOKER_LISTENER_KEY)));
  }

  public void destroy() {
    protocol.destroy();
  }

}

try {
  clazz.getConstructor(type);
  Set<Class<?>> wrappers = cachedWrapperClasses;
  if (wrappers == null) {
    cachedWrapperClasses = new ConcurrentHashSet<Class<?>>();
    wrappers = cachedWrapperClasses;
  }
  wrappers.add(clazz);
} catch (NoSuchMethodException e) {

Set<Class<?>> wrapperClasses = cachedWrapperClasses;
if (wrapperClasses != null && wrapperClasses.size() > 0) {
  for (Class<?> wrapperClass : wrapperClasses) {
    instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
  }
}

public abstract class ExporterListenerAdapter implements ExporterListener {

  public void exported(Exporter<?> exporter) throws RpcException {
  }

  public void unexported(Exporter<?> exporter) throws RpcException {
  }

}