OSGi, Maven and Scala

I’m inspired by Neil Barlett’s experiment on writing OSGi bundles in scala. This blogpost will show you how to compile OSGi bundles written in scala using pax-construct.

First here’s the modified source from Neil’s blog post:

// ------------------------ An OSGi service interface ------------------------------
package com.raverun.scala;

trait ExampleService
{
    def hello():String
}

// -------------------- The service implementation ------------------
package com.raverun.scala.internal;

import com.raverun.scala._

class ExampleServiceImpl extends ExampleService
{
    def hello():String = {
        return "Hello"
    }
}

// -------------------- our bundle activator --------------------------------
package com.raverun.scala.internal;

import org.osgi.framework._
import com.raverun.scala.ExampleService

class Activator extends BundleActivator
{
    var m_registration:ServiceRegistration

    def start( context: BundleContext )
    {
         var bundleNames = context.getBundles()  
                  .map   (b => b.getSymbolicName())  
                  .filter(b => b != context.getBundle());  
         Console.printf("Installed bundles: {0}",  
                         bundleNames.toString());  
   
         // register our service  
         m_registration = context.registerService( "com.raverun.scala.ExampleService",  
                                                   new ExampleServiceImpl(),  
                                                   null );  
    }  

    def stop( context: BundleContext )
    {
        if( m_registration != null )
            m_registration.unregister
    }
}

Except for the service definition, all the rest is lifted directly from Neil's blogpost. Software Prerequisites:

• pax-construct 0.6.3.
• maven 2.0.8
• eclipse 3.3.1.1

Create the pax-construct project

Before we can create bundles, it is mandatory to create a "project".

$ pax-create-project -g my.osgi.project -a scalaosgi

$ cd scalaosgi

For the rest of the article, I will refer to scalaosgi as PROJECTDIR

Next, we add the maven repositories for scala tools.

$ pax-add-repository -i scala-tools.org -u http://scala-tools.org/repo-releases

$ pax-add-repository -i scala-tools.org -u http://scala-tools.org/repo-releases -- -DpluginRepo

To round it up, add the bundle for the scala runtime into our provisioning setup.

$ pax-import-bundle -g org.scala-lang -a scala-library -v 2.6.1

Create a test bundle

Staying in PROJECTDIR, execute the following:

$ pax-create-bundle -p com.raverun.scala -n hello

$ cd hello

You are now inside the directory hello, which we'll refer to as BUNDLEDIR from now on.

Add the following dependencies to the pom.xml file.

    
      org.scala-lang
      scala-library
      ${scala.version}
      provided
    
    
      junit
      junit
      3.8.1
      test
    

Next, remove the generated java source code, and drop in the scala sources (found at the top of this article) into src/main/scala

$ rm -rf src/main/java

$ mkdir -p src/main/scala/com/raverun/scala/internal

Inform maven how to compile your scala sources

Change into directory PROJECTDIR/poms/compiled

Edit pom.xml and add the following snippets directly after the build element:

  
    src/main/scala
    src/test/scala
    
      org.scala-tools
      maven-scala-plugin
      
        
        
          compile
        
        
      
      
        ${scala.version}
      
    

    -----snipped--o<-----
  

Add maven settings

Change directory to ~/.m2/

Create a settings.xml file with the following contents.

  
    
      scalaosgi
      
        true
      
      
        2.6.1
      
    
  

Finishing touches

Change directory to PROJECTDIR

Compile and start the bundle

$ mvn install pax:provision

By default, it will start Apache felix.

Welcome to Felix.
=================

-> Installed bundles: Array(System Bundle, org.osgi.r4.compendium, org.apache.felix.shell, 
   org.apache.felix.shell.tui, my.osgi.project.scalaosgi.hello, scala_library)
-> ps
START LEVEL 6
   ID   State         Level  Name
[   0] [Active     ] [    0] System Bundle (1.0.1)
[   1] [Active     ] [    1] org.osgi.r4.compendium (1.0.0)
[   2] [Active     ] [    1] Apache Felix Shell Service (1.0.0)
[   3] [Active     ] [    1] Apache Felix Shell TUI (1.0.0)
[   4] [Active     ] [    5] my.osgi.project.scalaosgi.hello [com.raverun.scala] (1.0.0.SNAPSHOT)
[   5] [Active     ] [    5] Scala Library Bundle (2.6.1)
->