Creating Google wave robots in Grails

Updated 17/11: A grails plugin for Wave have been released see MasteringWave for more information.

I just got access to Google wave, where I would like to create a robot. A robot is a participant in the wave conversation and can do the same as everyone else in the wave. Wave robots can currently only be used by applications running on Google App-engine, so you need access to App-Engine. You can get this access here.

The application that I’m using is running grails, so it needs to fit into that application. When you read the robot functional specification, robots should extend AbstractRobotServlet. In grails Apps you have Controllers and no servlets, so this is a bit tricky. But really easy, when you find the trick.

To create your app, you need to create a grails app, to be deployed in app-engine using the Grails app-engine plugin. Follow the guide on the page and you should have an app running on app-engine.

I’ll use the wave robot tutorial as starting point for the app. The first thing you need is to download the following files and place them in the ./lib folder of your project.

  • wave-robot-api.jar
  • json.jar
  • jsonrpc.jar

The you need to create a capabilities.xml file. This is a configuration file, telling wave what your app responds to. capabilities.xml should be placed in the folder ./web-app/_wave/

<?xml version="1.0"?>
<w:robot xmlns:w="">
    <w:capability name="blip_submitted"/>

You can add as many capabilities as you want. Remember the version element should correspond to you application appspot version.

Update: For a clarification on the version numbering see

You can add the servlet file that need to be extended. This is done by placing the file in the ./src/groovy or ./src/java in your project. If it is a groovy file, it should probably be place4d in the groovy folder. You should maintain the package path within these folders. Create the following file ./src/groovy/com/wave/ParrotyServlet.groovy. (It is not very groovy code, but it is a start)

package com.wave
class ParrotyServlet extends  AbstractRobotServlet {
  public void processEvents(RobotMessageBundle bundle) {
    Wavelet wavelet = bundle.getWavelet();

      if (bundle.wasSelfAdded()) {
        Blip blip = wavelet.appendBlip();
        TextView textView = blip.getDocument();
        textView.append("I'm alive!");

      for (Event e: bundle.getEvents()) {
        if (e.getType() == EventType.BLIP_SUBMITTED) {
          Blip blip = wavelet.appendBlip();
          TextView textView = blip.getDocument();
          textView.append("Copying: " + e.getBlip().getDocument().text);


Then you need to add the servlet mapping this is done by installing the template. Run the following command, when you are in your project.

grails install-templates

Then you can edit the file ./src/templates/war/web.xml and add the servlet and the serveletmapping. This is done with the following elements. Remember that two elements should be placed after corresponding elements; otherwise the XML is not valid.



Deploy the service, and you can test you application. Create a new wave. Add you robot with the name <yourappspotname> Try to add a comment and you should get something like this screencast.

This is not a very functional robot, but it works. To store data you can use a service, which can be called from the servlet.

SAP PI XML Mappings using groovy

Creating XML mapping in Java have for me always been difficult, it has been possible but I would prefer other tools. I was looking at scripting languages like Ruby/JRuby or Groovy for creating some web apps. Those languages seem quite hot right now. On the SCN Wiki a group has implemented the Grails (groovy on Rails) on the Netweaver system, as Composition on Grails. With this tool it is possible to applications with a Webdynpro look and feel. Grails is a framework for creating webapps with less coding.

Groovy is a scripting language designed on the basis of Java. Groovy script is compiled into Java classes, and both Java and Groovy can be mixed. This makes the implementation easier, just start writing Java and when you feel like use some of the smarter features of Groovy you can use them.

While I was looking at Grails, I thought that I would be possible to use it in PI. One place could be in java mappings. I’ll describe the steps that I have taken to implement this.

  1. Download and install the groovy library
  2. Get the Groovy plugin to Eclipse, this make developing much easier.
  3. Create a new Eclipse project
  4. Insert the aii_map_api.jar in the project, to be able to implement Streamtransformation service.
  5. Create a new Groovy file in the source folder, with the name GroovyMapIdoc.groovy, then Eclipse know that it is a groovy file.
  6. Create the mapping of your file. I have attached my example code bellow.
  7. Compile the Groovy files using the context menu on the GroovyMapIdoc.groovy file.
  8. Zip the content of the bin-groovy in the project folder and upload it, as an imported archive in the Integration builder. Alternative use ant build to create the zip files.
  9. Upload the two files Groovy-1.6.1.jar and asm-2.2.3.jar as imported archives. They can be found in <GROOVY_HOME>\lib
  10. Activate and use the mapping.

I would expect people trying this to have a good knowledge of using XI or PI Java mappings, because it is a requirement for the development of mappings.

One example I always have considered, was my first challenging mapping experience. Posting financial post with more than 1000 lines to the FIDCCP02 idoc. The FIDCCP02 only accepts 999 lines. The posting can be created multiply idocs with 998 lines and the post a balance on each item. This way all documents will balance.

The document is transformed from the left document to the right. I have for this example used a max size of 3 to make testing easier.

The code that I have used for the mapping is.

package com.figaf.mapping

import java.util.Map;

import groovy.xml.MarkupBuilder

class GroovyMapIdoc implements StreamTransformation{

   Map param;
    void setParameter(Map param) {
        this.param = param;
    // Number of lines pr idoc
    def step=3
     * Implementation of the execution method
    void execute(InputStream input, OutputStream out) {

        // Parse the input using the XMLSlurper
        def FICCP01 = new XmlSlurper().parse(input)
        // get the different lines using the GPath
        def Lines = FICCP01.IDOC.LINE
        // create a writer example
        def writer = new OutputStreamWriter(out)
        def xml = new MarkupBuilder(writer)
        // create the root element and fill data into it.
            // get the number of idocs to be created.
            def numIdocs =   Lines.size()/step + (Lines.size()%step>0?1:0)  
            // loop for each idoc
            for ( i in 0..numIdocs-1 ) {
                // find the limit for the current idoc
                def max = Math.min( Lines.size(), i* step+2)
                // create sum ellement to create balances
                def sum = 0.0;
                 def lineno=1;
                    // create the number segment, using GPATH
                    NR(FICCP01.IDOC.NR )
                    // for each line in the range do the following
                         // create a  new Line node, in the out put element
                         // with the following content
                   // update the sum
                  sum +=oldline.Amount.toBigDecimal()
                    // create a balancing line, with balances the result

        // write the xml to output

Behind the scenes the Groovy file is changed in to java classes. Because Java does not support Closures natively different subclasses are created. Try to have a look on them using a decompiler like jad.


Groovy could be a way to improve the how java mappings are created. The XML generation is easier to handle then how it would have been created in Java and it is more powerful than XSLT. It takes some effort to get use to the closures concept of Groovy and the other notation, but it seems to work real well.

I don’t think the performance issue with the mapping is a problem. There is an overhead to load the groovy libraries and the code is probably not as optimized if it was written directly in java. I have not made any measurements for this.