Hi Tim, hi Jürgen,
thanks for your detailed answers.
Just to wrap it up so I didn't get something wrong:
A service is an object with an interface and properties registered in
the OSGi service registry and can be seen as an OSGi primitive for
bundle interoperation.
SCR is just a DI Framework that takes OSGi's dynamism into account and
additionally registers all its components (declarative services) as
services in the OSGi service registry.
@Tim: I might have expressed myself ambiguously. I didn't want to
propose to change the DS specification which standardizes how services
can be defined declaratively and also describes the behavior of a SCR
implementation.
What I instead intended to do was to ask if it would be
possible/sensible for a SCR implementation (e.g., Apache Felix SCR) to
also offer an API as mentioned before, so that I can write an Extender
that takes non-annotated classes at runtime and tell an SCR
implementation which fields/methods have to be treated as if they were
annotated with DS annotations.
However, if that is what you understood from my last mail anyway then I
still seem to be too dumb to get why such an API would be a request for
a radically different component model, e.g., why it makes such a
difference if the SCR instantiates a component because of an XML it
reads or because another entity commands it to do so. The information
that is given for the instantiation would be the same on the imperative
as on the declarative way I think.
@Jürgen: I don't think this would work in my case, as I need a reference
to the instance created. So when I create an instance via ConfigAdmin
then I usually don't get back a reference to the instance that is
created by the ConfigAdmin, but only have a reference on the
configuration I used to create a new instance. Or am I wrong?
Kind regards,
Thomas
------ Originalnachricht ------
Von: "Jürgen Albert via osgi-dev" <osgi-dev@mail.osgi.org>
An: osgi-dev@mail.osgi.org
Gesendet: 22.02.2019 15:34:16
Betreff: Re: [osgi-dev] SCR API
As an Addition to the things already suggested:
Taking your example I would create the MainView as follows:
@Route("")
@Component(name="MainView ", service=HasElement.class,
configurationPolicy=Required, scope=PROTOTYPE)
public class MainView extends VerticalLayout{
@Reference //what ever is required here
SomeService someService;
}
You can then use the Configurator or Config Admin to create you
component and even your someService target binding. Here is an example
for the Configurator would need to be translated to the ConfigAdmin if
you want to do this programmatically.
{
":configurator:resource-version": 1,
"MainView~instance1":
{
"someService.target": "(fancy.service.id.prop=fizzbuzz)"
}
}
Regards,
Jürgen.
Am 22/02/2019 um 10:29 schrieb Tim Ward via osgi-dev:
Hi Thomas,
I’m not sure that there is a naming issue here, but possibly a
different misunderstanding.
From my understanding there are two kinds of "services”:
This is not really accurate. There is only one kind of service in
OSGi, and it’s an object which has been registered with the service
registry. It is always registered by a call to
context.registerService(...). It doesn’t matter whether this action is
taken directly by your bundle, or on your bundle’s behalf by an
extender bundle. The fact that all services are the same is important
because this is how bundles interoperate. Your bundles can use any
mechanisms that they like internally and they can still interact with
other bundles that may be using the same, or different, internal
details.
2) "Fancy services" aka DS managed by a SCR. I specify those
declaratively via annotations, they have a lifecycle and can have
references to other services/components via annotations like
@Activate/@Deactivate (Lifecycle) and @Reference. Those I will call
components for the rest of this mail.
There are a large number of different component models around in Java.
These provide lifecycle management and injection for your objects. In
the case of OSGi aware component models they also provide support for
registering the object instance as a service (using
context.registerService()).
For Declarative Services the programming and configuration model is
declarative - you describe how you want your component’s lifecycle to
look using XML (or annotations to generate the XML). This XML is
packaged into your bundle and used by a Service Component Runtime (an
implementation of the DS specification) at runtime to find and manage
your component.
Components on the other side have references and lifecycle methods,
but in order to instantiate them programmatically I have to force a
developer to annotate the class with
@Component(scope=ServiceScope.PROTOTYPE) and then use
ServiceObjects<type>#getService() to instantiate/register it.
This procedure can be error-prone, e.g., when I assume that scope is
always PROTOTYPE but the developer forgot to set it to this value.
This problem came up during my discussion with Vaadin for a Flow-OSGi
integration.
This is really a decision that needs to be made by the component
developer. It doesn’t always make sense for a component to be
PROTOTYPE scoped, and they need to be aware that there may be multiple
instances created
In this context it would be great if there were a possibility to
programmatically create components (not services) where I can tell
SCR what fields/methods have to be treated as @Reference or lifecycle
methods and let SCR do the heavy lifting.
This is not what SCR does. SCR is a declarative component model, not a
programmatic one. There is no “DS builder API” for creating
components. If you want a builder API for creating a component then
you need to use a component framework that works in this way. As Ray
pointed out in a previous mail chain there is the Apache Aries
Component DSL. You could also use Apache Felix Dependency Manager.
Would such an API make sense? Or would it even be possible?
I think in general this would be very useful in order to create OSGi
integrations for third-party libs that need to interact with DS in
OSGi.
This isn’t really a question of third party libraries interacting with
DS, it’s a request for a radically different component model with some
DS-like capabilities. There are already framework implementations in
the world that provide what you’re looking for, just not using DS.
Best Regards,
Tim
On 21 Feb 2019, at 18:07, Thomas Driessen via osgi-dev
<osgi-dev@mail.osgi.org> wrote:
Hi BJ,
sorry for being imprecise. I sometimes get confused regarding the
proper naming in OSGi. I will try to clear things up by defining what
my understanding is about services:
From my understanding there are two kinds of "services":
1) "Old school Services": I usually register those programmatically
via context.registerService(...). Those services are just POJOs with
a little bit metadata, i.e., properties, and a well-defined
interface. Those I will call services for the rest of this mail.
2) "Fancy services" aka DS managed by a SCR. I specify those
declaratively via annotations, they have a lifecycle and can have
references to other services/components via annotations like
@Activate/@Deactivate (Lifecycle) and @Reference. Those I will call
components for the rest of this mail.
The difference between both (as far as I understand it) is that
services can be instantiated and registered programmatically, but are
not managed by SCR and therefore have no references and lifecycle
methods.
Components on the other side have references and lifecycle methods,
but in order to instantiate them programmatically I have to force a
developer to annotate the class with
@Component(scope=ServiceScope.PROTOTYPE) and then use
ServiceObjects<type>#getService() to instantiate/register it.
This procedure can be error-prone, e.g., when I assume that scope is
always PROTOTYPE but the developer forgot to set it to this value.
This problem came up during my discussion with Vaadin for a Flow-OSGi
integration.
In this context it would be great if there were a possibility to
programmatically create components (not services) where I can tell
SCR what fields/methods have to be treated as @Reference or lifecycle
methods and let SCR do the heavy lifting.
In Flow this would enable me to easily instantiate all classes that
are annotated with Vaadin's @Route annotation and register them as
components with scope PROTOTYPE and also to encorporate stuff like
references and lifecycle methods with my own annotations.
So for a class that looks like this:
@Route("")
public class MainView extends VerticalLayout{
@OSGiRef
SomeService someService;
}
I could call some imaginary API like this:
scr.createCmp(MainView.class)
.setScope(PROTOTYPE)
.setService(HasElement.class)
.addReference(someService);
and SCR would create this comopnent at runtime, inject the service
someService and then return this instance so that a third-party lib
can interact with it, while SCR still controls the lifecycle and
coming/going of referenced services/components.
Would such an API make sense? Or would it even be possible?
I think in general this would be very useful in order to create OSGi
integrations for third-party libs that need to interact with DS in
OSGi.
I hope this clarified my former email.
Kind regards,
Thomas
------ Originalnachricht ------
Von: "BJ Hargrave" <hargr...@us.ibm.com>
An: thomas.driessen...@gmail.com
Gesendet: 21.02.2019 14:48:18
Betreff: Re: Re[2]: [osgi-dev] SCR API
I am not what you mean by a "possiblity to register services in a
way to get references injected at runtime". Those are the different
sides of a service: The provider of the service and the consumers of
a service. Each side can use different models to interact. One can
register with the service API and the other can consume with DS,
CDI, etc. So service consumers do not need to care how the service
provider is implemented. So you can used DS to @Reference services
which have been registered by any method.
Because everything is a service in the framework's service registry,
each side of the service interaction can be written using different
models.
--
BJ Hargrave
Senior Technical Staff Member, IBM // office: +1 386 848 1781
OSGi Fellow and CTO of the OSGi Alliance // mobile: +1 386 848 3788
hargr...@us.ibm.com
----- Original message -----
From: "Thomas Driessen" <thomas.driessen...@gmail.com>
To: "BJ Hargrave" <hargr...@us.ibm.com>
Cc:
Subject: Re[2]: [osgi-dev] SCR API
Date: Thu, Feb 21, 2019 7:37 AM
Hi BJ,
is there a possiblity to register services in a way to get
references injected at runtime, i.e., something like the @Reference
funtionality but for services registered programmatically?
I think this would be a great enhancement for third-partyy
libraries who want to plug in into OSGi's DI framework.
Kind regards,
Thomas
------ Originalnachricht ------
Von: "BJ Hargrave" <hargr...@us.ibm.com>
An: thomas.driessen...@gmail.com; osgi-dev@mail.osgi.org
Cc: osgi-dev@mail.osgi.org
Gesendet: 21.02.2019 13:21:06
Betreff: Re: [osgi-dev] SCR API
There is not plan for Declarative Services to have an API for
imperatively creating components/services. The whole point of
Declarative Services is the declarative nature of it. You can
always use the service APIs of the framework to create services.
Or something like felix dependency manager.
--
BJ Hargrave
Senior Technical Staff Member, IBM // office: +1 386 848 1781
OSGi Fellow and CTO of the OSGi Alliance // mobile: +1 386 848
3788
hargr...@us.ibm.com
----- Original message -----
From: Thomas Driessen via osgi-dev <osgi-dev@mail.osgi.org>
Sent by: osgi-dev-boun...@mail.osgi.org
To: "OSGi Developer Mail List" <osgi-dev@mail.osgi.org>
Cc:
Subject: [osgi-dev] SCR API
Date: Thu, Feb 21, 2019 7:16 AM
Hi,
currently I'm debating on a Vaadin FLow issue how to best create
components in OSGi programmatically. The answer of my last
question on this mailing list regarding this topic was to use
scope=PROTOTYPE and then ServiceObjects<Type>#getService(). This
is a solution far better than the approach I used before but
still has some flaws, resulting in the following question:
Is there (or is it planned to create) an API for SCR to
programmatically create components at runtime?
I think of something like the Apache Felix DependencyManager
where I can register services but not components (with refrences
and stuff).
What I think of would be something like this:
scr.createCmp(Class class)
.setActivateMethod(...)
.setReferenceField(...)
.etc...
Kind regards,
Thomas
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--
Jürgen Albert
Geschäftsführer
Data In Motion Consulting GmbH
Kahlaische Str. 4
07745 Jena
Mobil: 0157-72521634
E-Mail: j.alb...@datainmotion.de
Web: www.datainmotion.de
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Rechtliches
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