Tutorial: How to create a remote OSGi service

In this article you will learn how to create a remote OSGi service from a "local" OSGi service using R-OSGi. The OSGi service for an user manager is published by the Activator of the service bundle:

public class Activator implements BundleActivator {
    public void start(final BundleContext context) throws Exception {
        context.registerService(IUserManager.class.getName(), new UserManager(), null);
        System.out.println("Service registered.");
    }

    public void stop(final BundleContext context) throws Exception {}
}

The Activator of the application bundle uses the service:

public class Activator implements BundleActivator {
    public void start(final BundleContext context) throws Exception {
        final ServiceReference serviceRef = context.getServiceReference(IUserManager.class.getName());
        if (serviceRef == null) {
            System.out.println("Service not found!");
        } else {
            final IUserManager userManager = (IUserManager) context.getService(serviceRef);

            try {
                System.out.println("All user names:");
                final List<String> names = userManager.getUserNames();
                for (final String name : names) {
                    System.out.println("Name = " + name);
                }
            } finally {
                context.ungetService(serviceRef);
            }
        }
    }

    public void stop(final BundleContext context) throws Exception {}
}

Now you have to verify that R-OSGi is installed on your local Eclipse. Activate the view "Plug-ins" and search for a bundle named ch.ethz.iks.r_osgi.remote. If it is already there, you may skip the following installation procedure.

The easiest way to install R-OSGi into your Eclipse is to install the Eclipse Communication Framework (ECF). Use one of the following update sites:

• Eclipse 3.4: http://download.eclipse.org/rt/ecf/2.0/3.4/updateSite/site.xml
• Eclipse 3.3: http://download.eclipse.org/rt/ecf/2.0/updateSite
  

After the download of the plug-ins, their installation and the restart of the Eclipse IDE the R-OSGi bundle will be available in the "Plug-ins" view.

First, you have to add the bundle ch.ethz.iks.r_osgi.remote to the list of required plug-ins. Do this for both the application and the service bundle. Then you have to mark the published OSGi service as remote service (inside the Activator of the service bundle):

  public void start(final BundleContext context) throws Exception {
      final Hashtable properties = new Hashtable();
      properties.put(RemoteOSGiService.R_OSGi_REGISTRATION, Boolean.TRUE);
      context.registerService(IUserManager.class.getName(), new UserManager(), properties);
      System.out.println("Service registered.");
  }

That was easy! Using the remote service requires a little bit more code. Instead of getting the user manager service directly from the service registry, you have to get the R-OSGi service from the service registry. Then you have to query the R-OSGi service for the remote user manager services. The code inside the Activator of the application bundle looks like this:

  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://205.207.25.9:9278"));

              final RemoteServiceReference[] references = remote.getRemoteServiceReferences(
                  new URI("r-osgi://205.207.25.9:9278"), IUserManager.class.getName(), null);
              if (references == null) {
                  System.out.println("Service not found!");
              } else {
                  final IUserManager userManager = (IUserManager) remote.getRemoteService(references[0]);

                  System.out.println("All user names:");
                  final List<String> names = userManager.getUserNames();
                  for (final String name : names) {
                      System.out.println("Name = " + name);
                  }
              }
          } finally {
              context.ungetService(serviceRef);
          }
      }
  }

Now you should test the remote OSGi service. Create a run configuration for the service and run it. Then create a run configuration for the application and run it. Depending on your user manager implementation you should see something like this (Console of the application):

osgi> All user names:
Name = Charly
Name = Dennis
Name = Ed

You may download the source code from here.