Fantom can not override overloaded methods. How to work around this?

(I try to write WebSocketHandler in webbit.)

There is no fix for that - it is probably still the #1 issue with Java FFI. You need to drop down and create a peer class or native Java class.

I created jar with java class

package org.webbitserver.handler;

import org.webbitserver.BaseWebSocketHandler;
import org.webbitserver.WebSocketConnection;

abstract public class RefineWebSocketHandler extends BaseWebSocketHandler{

  abstract public void onMsg(WebSocketConnection connection, String msg);

  @Override
  public void onMessage(WebSocketConnection connection, String msg) throws Exception {
    onMsg(connection,msg);
  }
}

and add as dependency for my pod.