How to unregister an OSGI/Blueprint Service from within the Service? - osgi

Question

In my application I have a Service ChatProtocolClient. The implementation is a tcp client which connects to a remote server in the blueprint "init-method" and disconnects in the "destroy-method".
I also have another bundle that uses this ChatProtocolClient's connection to read and post messages from a channel, ChatChannel.
Currently I have an xml file that creates a bean of the ChatProtocolClient, and creates a bean ChatChannel in which a reference to the created ChatProtocolClient service is injected.
But how can I handle disconnects from the server? I'd want to tell the Blueprint framework that my ChatProtocolClient instance is unusable now and it should unregister this instance.
Preferably Blueprint would then automatically call the destroy-method on all dependent beans (beans in which Blueprint injected this service reference) and initialize a new ChatProtocolClient bean and all beans that were destroyed because the dependency failed.
How can this be done?

Answer 1

I found a way to implement this. In this solutions it's not Blueprint that recreates instances of all dependent services. It goes like this:
Connection "Watchdog" beans.
Instead of creating "ChatProtocolClient" Beans, I created ConnectionWatchDog beans from xml. In these beans the BundleContext is injected and the connection properties are set from the .xml file.
The ConnectionWatchDog then tries to create/connect a ChatProtocolClient instance. If connection succeeds, it registers a service in the BundleContext (with bundleContext.registerService(..)). The ServiceRegistration is kept in the watchdog. The watchdog tests the connection on set interval (it runs it's own Thread). If the connection appears to have failed; the watchdog calls the serviceRegistration.unregister() and cleans up the remainders of the client connection instance, ands starts the whole proces of creating, connecting and registering an new ChatProtocolClient instance.
The ChatChannel
The ChatChannel is now configured in Blueprint with a . The xml looks like this:
<blueprint xmlns=...>
<reference-list id="chat-connection" member-type="service-object" interface="com.example.ChatProtocolClientInterface">
<reference-listener bind-method="onBind" unbind-method="onUnbind" ref="Channel1"/>
</reference-list>
<bean id="Channel1" class="ChatChannel" init-method="startUp">
<property name="chatProtocolClient" ref="chat-connection">
... some other properties ...
</bean>
</blueprint>
The member-type set to service-object, means that when a service is registered or unregistered, the ChatChannel will be informed with the "onBind" and "onUnbind" methods. As parameter, they'll get a ChatProtocolClientInterface instance.
I'm not sure whether this is the only or best solution, but it works for me. Note that with this example xml, you'll also need a setter for "chatProtocolClient"; currently I don't use the list that is set by blueprint and I only use the onBind and onUnbind methods.