FLOW OSGi Integration

WHAT

Trying to enhance current Flow OSGi integration, so that @Route/@RouteAlias annotated classes can be components (@Component annotated classes) too in an OSGi container

WHY?

Currently the efforts of Vaadin to make Flow (Vaadin 10+) OSGi compatible center around being able to run an existing Flow Application in an OSGi container. This is a great step forward, but might not be sufficient for people who do not want to port an existing Vaadin application into an OSGi container, but develop a Vaadin application as an OSGi enabled application, e.g., want to make use of OSGi's dependency injection mechanisms, i.e., Declarative Services.

Built on the premise, that one wants to develop a Flow application in OSGi I assume that this developer then wants to be able to define his @Route/@RouteAlias/(other?) annotated classes also to be a @Component in OSGi.

Contribute

You want to help making this work?

• PRs are highly welcome, just and start coding/browsing/whatever ;)
• Any question/suggestion? -> Submit an issue
• I've also opened an issue at Flow in order to get feedback from Vaadin directly on this integration.
• Any other stuff? Write me on Twitter

HOW?

The idea is as follows:

• Replace ServletContainerInitializers that are used in Flow to initialize a RouteRegistry with a corresponding BundleTracker that is able to track all the classes with @Route/RouteAlias/etc.. see FlowOsgiRouteTracker and FlowOsgiInitializer
• As we want to use @Route annotated classes also as @Components in OSGi we need to somehow bridge the Flow and OSGi world. This is done via two connection points, i.e., RouteRegistry and Instantiator
  • FlowOsgiRouteRegistry is used to dynamically add and remove Routes if used within an OSGi container. This is done via FlowOsgiRouteTracker scanning all classes for a @Route annotation and if present registering these classes as a services in OSGi so that they are dynamically injected to FlowOsgiRouteRegistry at runtime.
  • FlowOsgiInstantiator is used to create the route targets as OSGi @Components so that they can participate in OSGi' service lifecycle and reference other services that are registered in an Gi runtime. The instantiator is created within Flow via ServiceLoader which can be used by us to inject our Instantiator into Flow
• A developer that wants to create a Route for an OSGi application then only has to do something like the following:

@Route("")
@Component(factory="io.jatoms.example.MainView")
public class MainView extends VerticalLayout {

    @Reference
    GreeterService greeter;

    public MainView() {
        Button button = new Button("Click me",
                event -> Notification.show(greeter.greet()));
        add(button);
    }
}

This is an abstract view of the the logic flow of the solution:

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