appengine-web.xml

<?xml version="1.0" encoding="utf-8"?>
<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
    <application>twiliosandbox</application>
	<version>1</version>

	<!-- Allows App Engine to send multiple requests to one instance in parallel: -->
	<threadsafe>true</threadsafe>

	<!-- Configure java.util.logging -->
	<system-properties>
		<property name="java.util.logging.config.file" value="WEB-INF/logging.properties" />
	</system-properties>

	<inbound-services>
		<service>xmpp_message</service>
		<service>xmpp_presence</service>
		<service>xmpp_subscribe</service>
		<service>xmpp_error</service>
	</inbound-services>

</appengine-web-app>

ChatServlet.java

package com.twilio;

import java.io.IOException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;

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

import com.google.appengine.api.xmpp.JID;
import com.google.appengine.api.xmpp.Message;
import com.google.appengine.api.xmpp.MessageBuilder;
import com.google.appengine.api.xmpp.SendResponse;
import com.google.appengine.api.xmpp.XMPPService;
import com.google.appengine.api.xmpp.XMPPServiceFactory;
import com.twilio.sdk.TwilioRestClient;
import com.twilio.sdk.TwilioRestException;
import com.twilio.sdk.resource.factory.SmsFactory;
import com.twilio.sdk.resource.instance.Sms;
import com.twilio.sdk.verbs.TwiMLResponse;

@SuppressWarnings("serial")
public class ChatServlet extends HttpServlet {
	HashSet<String> subs = new HashSet<String>();

	// Send out a given message to all subscribers
	private void sendMessage(String body) {
		Iterator<String> it = subs.iterator();
		while (it.hasNext()) {
			String sub = it.next();
			String messageBody = "Group Chat: " + body;

			// We assume an at symbol is a chat client
			if (sub.indexOf("@") >= 0) {
				JID jid = new JID(sub);
				Message msg = new MessageBuilder().withRecipientJids(jid)
						.withBody(messageBody).build();

				boolean messageSent = false;
				XMPPService xmpp = XMPPServiceFactory.getXMPPService();
				SendResponse status = xmpp.sendMessage(msg);
				messageSent = (status.getStatusMap().get(jid) == SendResponse.Status.SUCCESS);

				if (!messageSent) {
					// TODO: Handle this case.
				}
			}

			// Otherwise, it's an SMS number
			else {
				TwilioRestClient client = new TwilioRestClient(
						"AC308ac9a994b1bd8b73ca0166442236c7",
						"1cb7a094ce91af64cc6bcc12a449fb1c");

				Map<String, String> params = new HashMap<String, String>();
				params.put("Body", messageBody);
				params.put("To", sub);
				params.put("From", "+16122948105");

				SmsFactory messageFactory = client.getAccount().getSmsFactory();

				try {
					Sms message = messageFactory.create(params);
					System.out.println(message.getSid());
				} catch (TwilioRestException e) {
					e.printStackTrace();
				}
			}
		}
	}

	// Handle Incoming SMS
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws IOException {
		try {
			TwiMLResponse twiml = new TwiMLResponse();

			// parse the body, looking for a command
			String smsBody = request.getParameter("Body");
			String smsFrom = request.getParameter("From");

			// Unsubscribe, if requested
			if (smsBody.startsWith("STOP")) {
				subs.remove(smsFrom);
				com.twilio.sdk.verbs.Sms bye = new com.twilio.sdk.verbs.Sms(
						"You have been unsubscribed.  Thank You!");
				twiml.append(bye);
			} else {
				// If they aren't subscribed, subscribe them
				if (!subs.contains(smsFrom)) {
					subs.add(smsFrom);
				}
				sendMessage(smsBody);
			}

			response.setContentType("application/xml");
			response.getWriter().print(twiml.toXML());

		} catch (Exception e) {
			e.printStackTrace();
			System.out.println(e);
		}
	}

	// Handle Incoming XMPP Chat messages
	public void doPost(HttpServletRequest req, HttpServletResponse res)
			throws IOException {
		XMPPService xmpp = XMPPServiceFactory.getXMPPService();
		Message msg = xmpp.parseMessage(req);

		JID fromJid = msg.getFromJid();
		String body = msg.getBody();

		// Unsubscribe, if requested
		if (body.startsWith("STOP")) {
			subs.remove(fromJid.getId());
		} else {
			// If they aren't subscribed, subscribe them
			if (!subs.contains(fromJid.getId())) {
				subs.add(fromJid.getId());
			}
			sendMessage(body);
		}
	}
}

web.xml

<?xml version="1.0" encoding="utf-8" standalone="no"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.5"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

	<servlet>
		<servlet-name>chat</servlet-name>
		<servlet-class>com.twilio.ChatServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>chat</servlet-name>
		<url-pattern>/_ah/xmpp/message/chat/</url-pattern>
	</servlet-mapping>
	<servlet-mapping>
		<servlet-name>chat</servlet-name>
		<url-pattern>/chat</url-pattern>
	</servlet-mapping>

	<servlet>
		<servlet-name>SystemServiceServlet</servlet-name>
		<servlet-class>com.google.api.server.spi.SystemServiceServlet</servlet-class>
		<init-param>
			<param-name>services</param-name>
			<param-value />
		</init-param>
	</servlet>
	<servlet-mapping>
		<servlet-name>SystemServiceServlet</servlet-name>
		<url-pattern>/_ah/spi/*</url-pattern>
	</servlet-mapping>

	<welcome-file-list>
		<welcome-file>index.html</welcome-file>
	</welcome-file-list>
</web-app>

Hello kwhinnery,

How this servlet can be used?
I'm asking because i need to write something like chat application in which arbitrary number of players will play prisoners dilemma game.
So i need something like a servlet that will receive messages from the clients, process them and broadcast messages backwards. The server would control the rounds, the player pairs etc. Is this servlet suitable for that? Is there some tutorial or help about hoe it can be used?

Regards,
Konstantin