r-OSGi remote OSGi example

In this post we will give a fair example of the workings of the OSGi services remoted through r-OSGi.

In order for the example to work, we must have an OSGi framework with the r-OSGi extension. Also, make sure the 9278 port on your system is free as r-OSGi uses it for its purposes.

Suppose we have a remotable service: HelloService, its interface: IHello and a client who declares a dependency on the service by pointing to its interfaces. It would also like to be able to access it remotely.

When a component declares it provides a service, the OSGi framework stores that information in its internal registry.

Download here the example's source code. You should be able to import everything inside Eclipse as-is. Inside you will find:

Interface - IHello.java:

package it.eng.test.remote.hello;
public interface IHello {   
    public String sayHello(String from);
}

Implementation - HelloService.java:

package it.eng.test.remote.helloservice;
import it.eng.test.remote.hello.IHello;
public class HelloService implements IHello{
    public String sayHello(String from){
        return "Hello from "+from;
    }
   
}

As we can see, the service offers a single, simple method which returns a String.

The service also uses a BundleActivator to register the service as remotable on the framework:

package it.eng.test.remote.helloservice;
import it.eng.test.remote.hello.IHello;
import java.util.Hashtable;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import ch.ethz.iks.r_osgi.RemoteOSGiService;
public class Activator implements BundleActivator {
    private BundleContext context;
    public BundleContext getContext() {
        return context;
    }
    @SuppressWarnings({ "rawtypes", "unchecked" })
    public void start(final BundleContext context) throws Exception {
          final Hashtable properties = new Hashtable();
          properties.put(RemoteOSGiService.R_OSGi_REGISTRATION, Boolean.TRUE);
          context.registerService(IHello.class.getName(), new HelloService(), properties);
          System.out.println("Service registered.");
      }   
    public void stop(BundleContext bundleContext) throws Exception {
        context = null;
    }
}

The client is, for simplicity only, composed just by the BundleActivator. When started it connects to the remote framework through its r-OSGi component to browse the available services and connect to the one it is interested in.

package it.eng.test.remote.helloconsumer;
import it.eng.test.remote.hello.IHello;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import ch.ethz.iks.r_osgi.RemoteOSGiService;
import ch.ethz.iks.r_osgi.RemoteServiceReference;
import ch.ethz.iks.r_osgi.URI;
public class Activator implements BundleActivator {
    private BundleContext context;
    public BundleContext getContext() {
        return context;
    }
    public void start(final BundleContext context) throws Exception {
          final ServiceReference serviceRef = context.getServiceReference(RemoteOSGiService.class.getName());
          if (serviceRef == null) {
              System.out.println("R-OSGi service not found!");
          } else {
              final RemoteOSGiService remote = (RemoteOSGiService) context.getService(serviceRef);
              try {
                  remote.connect(new URI("r-osgi://192.168.23.96:9278"));
                  final RemoteServiceReference[] references = remote.getRemoteServiceReferences(
                      new URI("r-osgi://192.168.23.96:9278"), IHello.class.getName(), null);
                  if (references == null) {
                      System.out.println("Service not found!");
                  } else {
                      final IHello hello = (IHello) remote.getRemoteService(references[0]);                      System.out.println(hello.sayHello(System.getProperty("os.name")));
                  }
              } finally {
                  context.ungetService(serviceRef);
              }
          }
      }
   
    public void stop(BundleContext bundleContext) throws Exception {
        context = null;
    }
}

The consumer firstly checks for the r-OSGi component presence, then uses it to connect to another r-OSGi enabled framework located at the address hardcoded in the Activator itself.

After the connection is established, he browses the remote framework's services to find the IHello implementation; if it is there, he attaches to it and prints "Hello from OS\_NAME" on standard output before unbinding from the service.