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Google Wave is a communication platform which merges the mediums email, forum, chat, instance messaging and wiki.

Google Wave can be separated into the product, the platform and the protocol. The product is what people can use, the platform allows developers to extend the Wave product and the protocol takes care of the synchronization between wave documents and other services.

The Google Wave product looks similar to the following screenshot.

Currently Google is running a beta program so not everyone can join Google Wave. You can sign-up to a waiting list on the Google Wave homepage . Google tries to grand access to Wave as fast as possible; currently access is usually given within a week after sign-up.

Google Wave has two environments. The Wave sandbox and the standard Wave Server. The standard wave server can be found https://wave.google.com/wave . The Wave sandbox system can be found here https://www.wavesandbox.com .

A wave is a threated conversation between one or several parties (people or programs (robots)).

A wave can be seen as an envelop which contains wavelets. A wavelet is a subset of a larger conversation (== wave). Access control can be given based on wavelets and all participants in a wavelet have full read and write access to the wavelet.

Wavelets contain blips. A Blip is a single, individual message. Blips can be have the status "published" or "draft". Blip stores their content in a XML document.

The Google Wave API operates either on wavelets or on blips.

The Wave protocol is based on XMPP ("Extensible Messaging and Presence Protocol"). The Google Wave protocol will automatically update all clients in case a change occurs.

Changes in a wave the are communicated as deltas between client and server to minimize the transferred data.

The following will develop a robot for Google Wave. This robot will be a "buzzword" detector. If you add the robot to a wave you can register certain words as buzzword. If buzzwords are used more then 3 times the robot will add "bingo" to the wave conversation.

Create a new "Web Application Project" "de.vogella.google.wave.firstrobot". Select only GAE support. The procedure for creating a project is described in Google App Engine .

Put the wave jars you downloaded from http://code.google.com/p/wave-robot-java-client/ in the folder "/war/WEB-INF/lib" and add them to the project build path.

Create the following Java class.

				
package de.vogella.google.wave.firstrobot;

import com.google.wave.api.AbstractRobot;
import com.google.wave.api.event.WaveletParticipantsChangedEvent;
import com.google.wave.api.event.WaveletSelfAddedEvent;

/**
 * Small sample bot for Google Wave to demonstrate bot behavior. Just says hello
 * and goodbye
 * 
 * @author Lars Vogel - Updated to new Wave API version
 */
public class MyWaveServlet extends AbstractRobot {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	@Override
	protected String getRobotName() {
		return "My first robot";
	}

	@Override
	protected String getRobotAvatarUrl() {
		return "http://www.vogella.de/img/common/LarsVogelAbout.jpg";
	}

	@Override
	public void onWaveletSelfAdded(WaveletSelfAddedEvent event) {
		event.getWavelet().reply("Hello Wave. I have been added");
	}

	@Override
	public void onWaveletParticipantsChanged(
			WaveletParticipantsChangedEvent event) {
		for (String participant : event.getParticipantsAdded()) {
			event.getWavelet().reply("\nHello " + participant);
		}

		for (String participant : event.getParticipantsRemoved()) {
			event.getWavelet().reply("\nGoodbye " + participant);
		}
	}

}

			

Map your servlet to the path "/_wave/" by changing the file "war\WEB-INF\web.xml" to the following.

				
<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
	<servlet>
		<servlet-name>WaveRobot</servlet-name>
		<servlet-class>de.vogella.google.wave.firstrobot.MyWaveServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>WaveRobot</servlet-name>
		<url-pattern>/_wave/*</url-pattern>
	</servlet-mapping>
</web-app>

			

The file "appengine-web.xml" needs to have the correction application id. You find this file in the folder "war/WEB-INF"

In step Google App Engine and Robots you should have created an application on the Google App Engine. In the file "appengine-web.xml" enter this application. For example I have registered "vogellawave" therefore my file looks like the following.

				
<?xml version="1.0" encoding="utf-8"?>
<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
	<application>vogellawave</application>
	<version>3</version>
	<precompilation-enabled>true</precompilation-enabled>
	
	<!-- Configure java.util.logging -->
	<system-properties>
		<property name="java.util.logging.config.file" value="WEB-INF/logging.properties"/>
	</system-properties>
	
</appengine-web-app>
			

Deploy your application to the Google app engine by pressing the highlighted button.

See Google App Engine for Java for details on deployment.

The Google Wave Java library will automatically create on the GAE/J server a configuration file which describes the capacities of your robot based on the implemented methods. The the GAE/J server you find this file at "http://yourApplicatioinName.appspot.com/_wave/capacities.xml". Use a browser to check if this is available.

Create a new wave. Press add participant and type yourapplication@appspot.com, e.g. in my example vogellawave@appspot.com. The system will asked you if you want to add the robot to your contacts. Select yes. Once you added the robot to your wave it should add his greetings to your wave.

We will extend the simple robot. The enhanced robot will allow to register buzzwords via the "!addbuzzword word" command, show the available buzzwords via "!showbuzzwords" and reset the buzzword counter via "!reset". See later for an example. Thanks to Oliver Gierke who provided the initial implementation of the following robot.

Change your servlet to the following.

				package de.vogella.google.wave.firstrobot;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import javax.servlet.ServletException;

import com.google.wave.api.AbstractRobot;
import com.google.wave.api.Blip;
import com.google.wave.api.event.BlipSubmittedEvent;
import com.google.wave.api.event.WaveletSelfAddedEvent;

/**
 * Small sample bot for Google Wave to demonstrate bot behavior. Just says hello
 * and goodbye
 * 
 * @author Lars Vogel - Updated to new Wave API version
 */
public class MyWaveServlet extends AbstractRobot {
	private static final long serialVersionUID = 1L;
	private static final String COMMAND = "\n!add";
	private static final String RESET_COMMAND = "\n!reset";
	private static final int COUNT_TO_WIN = 3;

	private List<String> buzzwords;
	private int count;

	// This defines the robot name for Google Wave
	@Override
	protected String getRobotName() {
		return "Buzzword Bot";
	}

	// This defines the picture for the Google Wave robot
	@Override
	protected String getRobotAvatarUrl() {
		return "http://www.vogella.de/img/common/LarsVogelAbout.jpg";
	}

	@Override
	public void init() throws ServletException {

		buzzwords = new ArrayList<String>();
		buzzwords.addAll(Arrays.asList("Wave", "Google", "Android", "GTUG",
				"DevDusk"));
		count = 0;
	}

	// By defining an event listener Wave knows that it should send these events
	// to your robot, here we listening the event that the robot is added to a
	// wave
	@Override
	public void onWaveletSelfAdded(WaveletSelfAddedEvent event) {
		// If you add text to a wavelet (creating a blip) you have to start the
		// text
		// with "\n"
		event.getWavelet().reply("\nBuzzword Bot has been added.");
	}

	@Override
	public void onBlipSubmitted(BlipSubmittedEvent event) {
		Blip blip = event.getBlip();
		if (!maybeLearnBuzzword(blip)) {
			detectBuzzwordIn(blip);
			bingoWon(blip);
		}
		eventuallyReset(blip);

	}

	/**
	 * @param blip
	 */
	private void bingoWon(Blip blip) {
		if (count >= COUNT_TO_WIN) {
			blip.getWavelet().reply("\nBuzzword BINGO!  ");
			count = 0;
		}
	}

	/**
	 * @param blip
	 */
	private boolean maybeLearnBuzzword(Blip blip) {

		String text = blip.getContent();
		if (text.startsWith(COMMAND)) {
			String buzzword = text.substring(COMMAND.length(), text.length())
					.trim();
			buzzwords.add(buzzword);
			blip
					.getWavelet()
					.reply(
							String
									.format(
											"\nAdded %s to buzzwords! Owning %s buzzwords now!",
											buzzword, buzzwords.size()));
			return true;
		}
		return false;
	}

	private void detectBuzzwordIn(Blip blip) {

		String text = blip.getContent();

		for (String buzzword : buzzwords) {
			if (text.contains(buzzword)) {
				blip.getWavelet().reply("\nGotcha!");
				count++;
				break;
			}
		}
	}

	private void eventuallyReset(Blip blip) {

		if (blip.getContent().startsWith(RESET_COMMAND)) {
			count = 0;
			blip.getWavelet().reply("\nReseted!");
		}
	}

}

			

Re-deploy your servelet.

In Google Wave create a new Wave and add your robot to the wave.

See the following screenshot for a possible usage of the robot.

In case of problems you can check the log on the GAE. Please see How to access the log in Google App Engine .

https://wave.google.com/wave Google Wave System

http://code.google.com/apis/wave/extensions/robots/java-tutorial.html Google Wave Robots: Java Tutorial

http://code.google.com/apis/wave/guide.html Google Wave Developer Guide

http://wave-samples-gallery.appspot.com/ Google Wave Code Examples

http://code.google.com/p/wave-protocol/wiki/Installation Installation of your own Google Wave server

http://googlewavedev.blogspot.com/ Google Wave Blog

http://code.google.com/events/io/sessions/ProgrammingWithAndForGoogleWave.html Google Wave Technical Talk