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
