Idea.java

public interface IoResultCallback {
    void onSuccess();
    void onError(Throwable cause);
    
    default ChannelFutureListener asChannelFutureListener() {
        // Implement me
    }
    
    static IoResultCallback noop() {
        return ...;
    }
}

public interface ChannelPromise {
    ...
    IoResultCallback asIoResultCallback();
}

public interface ChannelHandlerContext {
    ....
    ChannelHandlerContext write(Object msg, IoResultCallback callback);
    ChannellFuture write(Object msg);
    
    ChannelHandlerContext flush(IoResultCallback callback);
    ChannellFuture flush();
    
    ChannelHandlerContext read(IoResultCallback callback);
    ChannellFuture read();
}

public interface ChannelHandler {

    default void write(ChannelHandlerContext ctx, Object msg, IoResultCallback callback) {
        ctx.write(msg, callback);
    }
    
    default void flush(ChannelHandlerContext ctx, IoResultCallback callback) {
        ctx.flush(callback);
    }
    
    default void read(ChannelHandlerContext ctx, IoResultCallback callback) {
        ctx.read(callback);
    }
}

public class NoListenerNeededExample implements ChannelHandler {
    @Override
    public void write(ChannelHandlerContext ctx, Object msg, IoResultCallback callback) {
        ... 
        ctx.write(msg, callback);
    }
}

public class ListenerNeededExample implements ChannelHandler {
    @Override
    public void write(ChannelHandlerContext ctx, Object msg, IoResultCallback callback) {
        ctx.write(msg).addListener(callback.asChannelFutureListener());
    }
}