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From Christian Schneider <ch...@die-schneider.net>
Subject Re: [DISCUSSION] Karaf Boot
Date Thu, 10 Sep 2015 07:05:11 GMT
Hi JB,

I support the idea of providing a simple startable artifact of karaf + 
fetures + config.

The injection annotations I do not like at all. A plugin like above 
should do one thing well. Doing injection well is difficult. There are 
already projects that provide support for this like pax-cdi, blueprint 
mave plugin, DS. We should only leverage existing injection frameworks and
not try to replace them.

What we could provide in from of annotations is the description of the 
assembly. Like features, configs, other customizations.

Spring boot also provides a way to create a complete container out of 
one single project. So it also embeds the java source and provides 
injections. I considers this to be rather a gimmic and demo feature not 
a thing that is really needed. A real OSGi application will always 
consist of
more than one bundle / maven project. So I think it is enough to just 
provide a way to package such exising bundles into a nice runnable 
artifact.

If you think the demoing aspect is very important then we could try to 
have sample code using DS annotations and the container config code in 
the same project. This is rarely a real life example but could show that 
we can be as small as spring boot.

To still have a nice starting point for people I propose we crerate a 
maven archetype that creates a project structure like this:
- main
  - service : A project defining and publishing a DS service
  - assembly or boot : A project defining the assembly config that 
creates the runnable artifact

Christian

Am 09.09.2015 um 16:32 schrieb Jean-Baptiste Onofré:
> Hi all,
>
> I worked on a prototype about Karaf Boot.
>
> Let me give you some backgrounds and discuss about that all together.
>
>  Why Karaf Boot ?
>  ----------------
> When you develop artifacts (bundles) to be deployed in Karaf, you can 
> see that the actual time that you spend on your business code is 
> finally largely less important that all the plumbing effort that you 
> have to do (writing OSGi Activator, or blueprint/scr descriptor, etc).
>
> It means that your "go to market" is longer, and we should provide 
> something that allows you to focus on your code.
>
> Even if SCR annotations is a very good step forward, some use cases 
> are not so easy to do (JPA, JTA for instance).
>
> And anyway, you have to prepare your pom.xml with different plugin and 
> dependency.
>
> Moreover, when you have your artifacts, you have to prepare Karaf 
> container, and deploy those artifacts there. Even if it's "container" 
> approach is the most important for me, we can give even more 
> flexibility by providing a way to embed and prepare Karaf in a ready 
> to execute jar/artifact.
>
>  What is Karaf Boot ?
>  --------------------
> Karaf Boot provides four components:
> * karaf-boot-parent is the Maven parent pom that your project just 
> inherit: that's all ! All plugins, dependencies, etc are described in 
> this parent, you even don't have to define packaging as bundle, 
> standard jar is fine.
> * karaf-boot (coming with karaf-boot-parent) provides annotations that 
> you use directly in your business code (like @Bean, @Service, 
> @Reference, @Inject, etc): again, your focus on your code, karaf-boot 
> deals with the plumbing.
> * karaf-boot-maven-plugin (coming with karaf-boot-parent) scan the 
> classes and generate a blueprint XML. For now, I'm using blueprint 
> generation (because we can cover lot of use cases, for instance, I 
> plan to provide @rest annotation that will generate blueprint XML with 
> cxf jaxrs server, etc).
> * karaf-boot-starter is the module providing a convenient way to 
> embed, configure and bootstrap Karaf.
>
> Just to illustrate this, let's take a look on the 
> karaf-boot-sample-simple.
>
> The pom.xml is really simple:
>
> <?xml version="1.0" encoding="UTF-8"?>
> <project xmlns="http://maven.apache.org/POM/4.0.0" 
> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
> xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
> http://maven.apache.org/xsd/maven-4.0.0.xsd">
>
>     <modelVersion>4.0.0</modelVersion>
>
>     <parent>
>         <groupId>org.apache.karaf.boot</groupId>
>         <artifactId>karaf-boot-parent</artifactId>
>         <version>1.0.0-SNAPSHOT</version>
>     </parent>
>
>     <artifactId>karaf-boot-sample-simple</artifactId>
>     <version>1.0.0-SNAPSHOT</version>
>
> </project>
>
> You can see, the only thing that the developer has to do: define 
> karaf-boot-parent as parent pom. That's all.
>
> Now, in the code, you have just one bean that we want to run:
>
> package org.apache.karaf.boot.sample.simple;
>
> import org.apache.karaf.boot.Bean;
> import org.apache.karaf.boot.Init;
>
> @Bean(id = "simple-bean")
> public class SimpleBean {
>
>     @Init
>     public void simple() {
>         System.out.println("Hello world");
>     }
>
> }
>
> You can see the @Bean and @Init karaf-boot annotations. The 
> karaf-boot-maven-plugin will generate the blueprint descriptor using 
> this.
>
>
>  Current Status
>  --------------
> I pushed Karaf Boot structure there:
>
> https://github.com/jbonofre/karaf-boot
>
> It's a mix of rewrapping of existing code (from aries, pax-exam, etc) 
> and additions.
>
> I created the annotations, I'm now working on the 
> karaf-boot-maven-plugin based on Christian's work in aries (I'm 
> actually scanning the boot annotations now, and generating the XML).
>
> I will push new changes later today and tomorrow.
>
>  Open Questions
>  ---------------
> * For now, I would prefer to be 'artifacts' and 'resources' generator: 
> I think it's better than to depend to a feature running in Karaf, but 
> it's open to discussion.
> * I'm now generating blueprint. Probably native OSGi or scr generation 
> can make sense.
> * I'm generating bundles: thanks to the Karaf4 features resolver, as 
> the bundles provide requirements/capabilities metadata, I think it's a 
> good start. However, maybe it's worth to be able to create features, 
> kar, profile.
>
> Thoughts ?
>
> Thanks,
> Regards
> JB


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