The OSGi Look

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Configuration Admin Service explained: the ManagedService interface

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As chapter 104.1 of the OSGi compendium specification states:

The Configuration Admin service is an important aspect of the deployment
of an OSGi Service Platform. It allows an Operator to set the configuration
information of deployed bundles.
Configuration is the process of defining the configuration data of bundles
and assuring that those bundles receive that data when they are active in the
OSGi Service Platform.

In simple words, the Configuration Admin service provides a simple way to

  • Write services that can be dynamically configured
  • Programmatically configure services

Write a dynamically configurable service

The simplest way to write a service able to receive new configurations at runtime is to implement the ManagedService interface, like in the example:

public class SmsService implements ManagedService
        //... sms service implementation here

	 * This method receives new Configuration Dictionaries
	public void updated(Dictionary properties) throws ConfigurationException 
		//configure here your service

The ManagedService is notified every time the Configuration Admin Service push a new configuration dictionary. In this case, the method update is called, giving the service the opportunity to re-configure itself.

To make the OSGi container aware of our SmsService, it is important to register it as a ManagedService like in the example:

public class SmsServiceActivator implements BundleActivator
	ServiceRegistration registration;
	public void start(BundleContext context) throws Exception 
		Dictionary properties = new Hashtable();
		properties.put("", "mySmsService");
		registration = context.registerService(ManagedService.class.getName(), 
                         new SmsService(), properties);
	public void stop(BundleContext context) throws Exception 
		if (registration!=null)
			registration = null;

Notice that the ManagedService is registered with a parameter; that’s the reference name we will need to use to configure that particular name.

Configure a service using the Configuration Admin Service

Once the SmsService is implemented, registered and deployed, it can be configured at runtime using a few lines of code:

ServiceReference caRef = bundleContext.getServiceReference(ConfigurationAdmin.class.getName());  

if (caRef != null) 
    ConfigurationAdmin configAdmin = (ConfigurationAdmin)  bundleContext.getService(caRef);  
    Configuration config = configAdmin.getConfiguration("mySmsService");

    Dictionary props = config.getProperties();
    if (props == null) 
       props = new Hashtable();
   // configure the Dictionary
   props.put("key", "value");

   //push the configuration dictionary to the SmsService

The code displayed above retrieves the ConfigurationAdmin service available in the OSGi platform, and invoke its getConfiguration method passing the of the service to be configured. The result of this invocation is a Configuration object, that expose the configuration Dictionary via the getProperties method.
After applying all the needed modifications to the configuration Dictionary, the update method pushes the configuration Dictionary to the ManagedService (Sms Service in our example)


Written by fdiotalevi

March 22, 2009 at 8:16 pm

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