In this episode, we are going to look at how you can write a Google Wave Robot using the Google plugin in Eclipse. We will then deploy it and host this robot in the Google App Engine cloud. This Robot is then live and can be added to any Wave and participate in the conversation.
It helps to see the final result before we start out. Even if you do not understand whats going on, just bear with me. So here is the screenshot:
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Let us dissect this screen and in the process, I can hopefully explain to you some Google Wave terminology in a straightforward manner without too many details. The main points are:
1. What you see in the screen above is a Google Wave that me (the person with the photo created). A Wave is a collaboration between one or more participants (human or Robots). 2. Since we need participants to make it meaningful, you can add one or more of them. All you need to do is click the + sign that you see on the top. And you can add one or more participants who are also signed up for Wave. In this case, my Robot GAEJ Application is hosted at http://gaejrobot.appspot.com and so I can add
[email protected] as a participant.
3. On adding the Robot participant, Google wave system pulls up its profile (image, etc) and adds it as a participant in the Wave that I created.
4. The Robot can receive events and it can respond to them. We shall see how to write them later (source code!!), but at this point it is enough to understand that the Robot can choose what events to listen to as the Wave collaboration happens and it can then react to them. So in the case of my GAEJ Robot, I have specified that I am interested in knowing when participants come and leave the Wave and when someone has submitted a message. 5. So you can see that the GAEJ Robot was notified when it was added to the Wave, so in response to that it printed out the message “Hi! Your GAEJExperiments Bot…..” at the bottom. Similarly, when I finished typing the message (Hello GAEJ Robot), the GAEJ Robot got notified. It then took the message and along with some metadata like ID and Creator Name, it simpy echoed back what I typed.
Hope this makes things clear. But a few more terms first : Wave, Wavelet and Blip. Let me keep it simple. In the above example, the Wave was the entire container. A Wave
consists of one or more Wavelets. A Wavelet can be thought of as a threaded
conversation that can go on within the wave (both public and private). And each Wavelet consists of one or more messages known as a Blip. A Blip is the actual message that was typed and submitted by the user. So when I typed “Hello GAEJ Robot” above, it was a
Blip.
I have simplified things a bit here but even if things are not clear at this point, do not worry. Once you get your code working, things will fall in place.
A final note above Google Wave Extensions. Extensions are the mechanism by which you can extend Google Wave by adding your own creations. Extensions are of two types : Gadgets and Robots. Gadgets are like mini-applications that run within the Google Wave client. They can be typically thought of as a UI which several participants can share at the same time. A Robot is a full blown participant in the Wave. It can be aware of most things happening in the Wave by subscribing to Events. It also has a lot of potential to modify things in the Wave like messages, etc. This article focuses on writing a Robot. If you are interested in a good summary of Google Wave Extensions and some key differences between a Gadget and a Robot, read it here.
OK, so enough of theory. Let us get down to coding. If you are new to developing with the Google Plugin for Eclipse, please read the earlier episodes to setup your environment (Episode 1 and Episode 5)
Create a New Project
We need to create a New Project first. Follow the steps below:
1. Either click on File –> New –> Other or press Ctrl-N to create a new project. Select Google and then Web Application project. Alternately you could also click on the New Web Application Project Toolbar icon as part of the Google Eclipse plugin.
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and give a name to your project. I have named mine MyFirstGoogleWaveRobot and I suggest you go with the same name so that things are consistent with the rest of the article. The Screenshot is shown below:
3. Click on Finish. This will generate the project and also create a sample Hello World Servlet for you. But we will be writing our own Servlet. So I suggest that you can delete the Servlet Java class and the mappings made in the web.xml or you can leave it for now since we are going to write our own.