Google App Engine Channel presence handler throwing exceptions

Question

I'm experiencing this with the SDK running locally on my Mac. I am trying to establish presence handling. I've created a simple servlet that does nothing but logging. However, I'm getting the following exception on any connection and disconnection event (though Channels appear to be working otherwise)...

Mar 14, 2013 8:04:25 PM com.google.apphosting.utils.jetty.JettyLogger warn
WARNING: /_ah/channel/disconnected/: javax.servlet.UnavailableException: java.lang.InstantiationException
Mar 14, 2013 8:04:38 PM com.google.apphosting.utils.jetty.JettyLogger warn
WARNING: /_ah/channel/connected/: javax.servlet.UnavailableException: java.lang.InstantiationException

I've registered that servlet for both connection and disconnection of channels in my web.xml...

  <servlet>
    <servlet-name>ChannelPresence</servlet-name>
    <servlet-class>com.readyposition.gaetestbed.ChannelPresenceServlet          
    </servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>ChannelPresence</servlet-name>
    <url-pattern>/_ah/channel/connected/</url-pattern>
  </servlet-mapping>

  <servlet-mapping>
    <servlet-name>ChannelPresence</servlet-name>
    <url-pattern>/_ah/channel/disconnected/</url-pattern>
  </servlet-mapping>

The handler (servlet) itself is quite basic...

package com.readyposition.gaetestbed;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.appengine.api.channel.ChannelPresence;
import com.google.appengine.api.channel.ChannelService;
import com.google.appengine.api.channel.ChannelServiceFactory;

@SuppressWarnings("serial")
public abstract class ChannelPresenceServlet extends HttpServlet {
    final static Logger logger =
            LoggerFactory.getLogger(ChannelPresenceServlet.class);

    @Override
    public void doGet(final HttpServletRequest req,
            final HttpServletResponse resp)
                    throws IOException, ServletException
    {
        processCommand(req, resp);
    }

    @Override
    public void doPost(final HttpServletRequest req,
            final HttpServletResponse resp)
                    throws IOException, ServletException
    {
        processCommand(req, resp);
    }

    public void processCommand(final HttpServletRequest req,
            final HttpServletResponse resp)
                    throws IOException, ServletException
    {
        final ChannelService channelService =
                ChannelServiceFactory.getChannelService();
        final ChannelPresence presence = channelService.parsePresence(req);

        logger.info("Channel Presence - clientId={}, isConnected={}",
                presence.clientId(), presence.isConnected());
    }
}

Any help would be appreciated.

score 1 · Answer 1 · answered Mar 15 '13 at 00:34

1

How embarrassing. Cut and paste error. My servlet class was erroneously abstract. Sigh. Fixed.

I saw several other people complaining about the same exception under different circumstances, and at least one relating to Channel presence. If one other person realizes that they have mistakenly left a servlet class as abstract then I suppose this will have been beneficial.

Thanks to anyone who tried to follow me down the rat hole.

answered Mar 15 '13 at 00:34

Chuck

1,788
2
15
28

If I should delete this whole post, let me know. – Chuck Mar 15 '13 at 00:35

Google App Engine Channel presence handler throwing exceptions

1 Answers1