Importing a Service

A bundle acquires one or more imported services by simply overridding the BaseBundleActivator inherited method getImportedServices(). For example:

  protected String[] getImportedServiceNames() {
    return new String[] {
      VendorService.SERVICE_NAME,
      NapkinService.SERVICE_NAME
    };
  }

The bundle activator's activate() method will only be called once the bundle has successfully acquired all the services described by the getImportedServiceNames() method. From inside the activate() method the imported services may be accessed by calling the inherited method getImportedSerivce(String) that takes as a parameter the name of a service. For example:

  protected void activate() {
    VendorService vendor = (VendorService) getImportedService(VendorService.SERVICE_NAME);
    NapkinService napkin = (NapkinService) getImportedService(NapkinService.SERVICE_NAME);
	//...  
  }

After the activate() method has been called losing an imported service because it has been unregistered from the OSGi framework results in the bundle activator's deactivate() method to be called. The deactivate() method is where the bundle activator should stop using all of its imported services.
After the deactivate() method has been called, re-acquiring all imported services will result in the bundle activator's activate() method being called once more.

It is often useful to write getter methods to make accessing imported services more convenient:

  private VendorService getVendorService() {
    return (VendorService) getImportedService(VendorService.SERVICE_NAME);
  }

  private NapkinService getNapkinService() {
    return (NapkinService) getImportedService(NapkinService.SERVICE_NAME);
  }

Allowing the activate() method to be a simple as:

  protected void activate() {
    VendorService vendor = getVendorService();
    NapkinService napkin = getNapkinService();
	//...  
  }