Hi Guozhang,
I'm going to drop in a little extra context from the preliminary PR
discussion (https://github.com/apache/kafka/pull/5344).
The issue isn't that it's impossible to use Streams within a Spring app,
just that the interplay between our style of construction/configuration and
Spring's is somewhat awkward compared to the normal experience with
dependency injection.
I'm guessing users of dependency injection would not like the approach you
offered. I believe it's commonly considered an antipattern when using DI
frameworks to pass the injector directly into the class being constructed.
Wladimir has also offered an alternative usage within the current framework
of injecting pre-constructed dependencies into the Properties, and then
retrieving and casting them inside the configured class.
It seems like this KIP is more about offering a more elegant interface to
DI users.
One of the points that Wladimir raised on his PR discussion was the desire
to configure the classes in a typesafe way in the constructor (thus
allowing the use of immutable classes).
With this KIP, it would be possible for a DI user to:
1. register a Streams-Spring or Streams-Guice (etc) "plugin" (via either of
the mechanisms he proposed)
2. simply make the Serdes, exception handlers, etc, available on the class
path with the DI annotations
3. start the app
There's no need to mess with passing dependencies (or the injector) through
the properties.
Sorry for "injecting" myself into your discussion, but it took me a while
in the PR discussion to get to the bottom of the issue, and I wanted to
spare you the same.
I'll respond separately with my feedback on the KIP.
Thanks,
-John
On Sun, Sep 30, 2018 at 2:31 PM Guozhang Wang <wangg...@gmail.com> wrote:
> Hello Wladimir,
>
> Thanks for proposing the KIP. I think the injection can currently be done
> by passing in the key/value pair directly into the properties which can
> then be accessed from the `ProcessorContext#appConfigs` or
> `#appConfigsWithPrefix`. For example, when constructing the properties you
> can:
>
> ```
> props.put(myProp1, myValue1);
> props.put(myProp2, myValue1);
> props.put("my_app_context", appContext);
>
> KafkaStreams myApp = new KafkaStreams(topology, props);
>
> // and then in your processor, on the processor where you want to construct
> the injected handler:
>
> Map<String, Object> appProps = processorContext.appConfigs();
> ApplicationContext appContext = appProps.get("my_app_context");
> MyHandler myHandler =
> applicationContext.getBeanNamesForType(MyHandlerClassType);
> ```
>
> Does that work for you?
>
> Guozhang
>
>
> On Sun, Sep 30, 2018 at 6:56 AM, Dongjin Lee <dong...@apache.org> wrote:
>
> > Hi Wladimir,
> >
> > Thanks for your great KIP. Let me have a look. And let's discuss this KIP
> > in depth after the release of 2.1.0. (The committers are very busy for
> it.)
> >
> > Best,
> > Dongjin
> >
> > On Sun, Sep 30, 2018 at 10:49 PM Wladimir Schmidt <wlsc....@gmail.com>
> > wrote:
> >
> > > Dear colleagues,
> > >
> > > I am happy to inform you that I have just finished my first KIP
> > > (KIP-378: Enable Dependency Injection for Kafka Streams handlers
> > > <
> > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > 378%3A+Enable+Dependency+Injection+for+Kafka+Streams+handlers
> > > >).
> > >
> > > Your feedback on this submission would be highly appreciated.
> > >
> > > Best Regards,
> > > Wladimir Schmidt
> > >
> >
> >
> > --
> > *Dongjin Lee*
> >
> > *A hitchhiker in the mathematical world.*
> >
> > *github: <http://goog_969573159/>github.com/dongjinleekr
> > <http://github.com/dongjinleekr>linkedin:
> kr.linkedin.com/in/dongjinleekr
> > <http://kr.linkedin.com/in/dongjinleekr>slideshare:
> > www.slideshare.net/dongjinleekr
> > <http://www.slideshare.net/dongjinleekr>*
> >
>
>
>
> --
> -- Guozhang
>
