Question

We have to support at least 2 versions of functionality at the same time. It can be in the web side or services, meaning we’ll have different layout for different users in the web or service implementation will be different for different users. We should be able to route the users based on their login to the right version of the web application / bundle.

We thought of something like this (please see bigger picture here https://i.stack.imgur.com/6NxhF.png).

Also is it possible to have multiple web applications / bundles deployed as one EBA? If yes, is it possible to share the session between these web apps / bundles? As we are new to OSGi, looking forward to any suggestion on the design we have chosen. Appreciate any help / suggestions on this.

Thanks,

Bab.

Answer 1

Yes, OSGi can help you a lot with this.

The architecture you have chosen looks fine, I would suggest perhaps also adding a ‘SessionManager’ as suggested by Christian.

Regarding the OSGi specifics you will need for this:

If you have two different versions of the “Services” bundle, which are packaged in the same Java packages, you should definitely define package versions when exporting them in the manifests:

In Services V1:

Export-Package: com.acme.foo;version="1.24"

and in Services V2

Export-Package: com.acme.foo;version="2.3"

You can then control which package is imported in the Web bundles by defining restrictions, e.g. like this for whole intervals:

Import-Package: com.acme.foo;version="[1.23, 2)"

The beauty of this is that due to the modularity of OSGi and the separate classloaders of the bundles both versions of com.acme.foo can be installed and used in the same system. You cannot achieve this in the “usual” Java setup, because there there is only one classloader and one version of the package will shadow the other.

You can see OSGi demos and examples for example here

This was about the packages and libraries.
Now about the actual service objects:

You could also have two versions of the same service published in the OSGi Service Registry. The easiest way to differentiate between the two is to use service properties when registering the service:

Hashtable properties = new Hashtable();
properties.put( "service_flavour",
"advanced" );
context.registerService(
SomeService.class.getName(),
this, properties );

You can then use the props to lookup the correct service in the Web bundles:

ServiceTracker someServiceTracker = new ServiceTracker(bc, "(&(objectclass="+SomeService.class.getName()+")(service_flavour=advanced))", null);
someServiceTracker.open();

Regarding your question about EBA – I am not sure what you mean. You can install as many bundles as you want in any OSGi framework, and they can all register under different aliases in the OSGi HTTP service. As long as the aliases don’t have a conflict with each other it is ok. You can also have one main servlet if you want, and distribute the handling of the different pages to other bundles without registering them as servlets too – your main web servlet could look them up in the OSGi service registry for example, and distribute the work. It all depends whether you expect more application logic/calculations etc, or is it more about formatting and representation of some existing data.

Hope this helps.