Usage of conditional in Karaf features

[Lars Kiesow <lk...@uos.de>]

Hi everyone,
I'm wondering how exactly the conditionals are supposed to be used in
Karaf features:


  <feature name="example" version="1.2.3">
    <conditional>
      <condition>xy</condition>
      ...
    </conditional>
    ...
  </feature>


I'm trying to activate a feature (or a list of bundles in that feature)
only if another feature specified in a condition is already installed.

I got this working alright, since I install these features dynamically
with some code anyway, but while it works, I am worried about potential
side-effects since I don't quite know how it is supposed to be working.

A simplified pseudo-code version of my code looks like this:


  // get installed features
  installedFeatures = featuresService.listInstalledFeatures()
  // iterate over available features
  for (Feature feature : featuresService.listFeatures()) {
    // get all conditions
    conditions = feature.getConditionals().getConditions()
    // check if a condition matches an installed feature
    if (conditions intersect installedFeatures) {
      // install feature
      featuresService.installFeature(feature);
    }
  }


Does anyone know if this could have any side-effects?

Or even better, can anyone give me a proper explanation or
documentation of how the conditionals in Karaf features work and how
they are supposed to be used?

Thanks,
Lars

Re: Usage of conditional in Karaf features

[Jean-Baptiste Onofré <jb...@nanthrax.net>]

Hi Lars,

Reusing your example:

     <feature name="example" version="1.2.3">
       <conditional>
         <condition>xy</condition>
	<bundle>foo</bundle>
       </conditional>
       ...
     </feature>

bundle foo will be installed only if condition predicate (feature xy) is 
true.
If later, the condition will be satisfied then foo will be installed.

Concrete example:

     <feature name="deployer" description="Karaf Deployer" 
version="${project.version}">
         <bundle 
start-level="26">mvn:org.apache.karaf.deployer/org.apache.karaf.deployer.features/${project.version}</bundle>
         <conditional>
             <condition>pax-url-wrap</condition>
             <bundle 
start-level="24">mvn:org.apache.karaf.deployer/org.apache.karaf.deployer.wrap/${project.version}</bundle>
         </conditional>
         <conditional>
 
<condition>req:osgi.extender;filter:="(&amp;(osgi.extender=osgi.blueprint)(version>=1.0))"</condition>
             <bundle 
start-level="24">mvn:org.apache.karaf.deployer/org.apache.karaf.deployer.blueprint/${project.version}</bundle>
         </conditional>
         <conditional>
             <condition>kar</condition>
             <bundle 
start-level="24">mvn:org.apache.karaf.deployer/org.apache.karaf.deployer.kar/${project.version}</bundle>
         </conditional>
     </feature>

it means:
1. wrap deployer will be installed only/when pax-url-wrap feature is 
installed
2. blueprint deployer will be installed only/when a blueprint provider 
is installed (osgi.extender)
3. kar deployer will be installed only/when kar feature is installed

The purpose is to have multi-form feature that triggers installation of 
resources (bundle, config, configfile) when the condition is satisfied.

Regards
JB

On 06/12/2021 21:58, Lars Kiesow wrote:
> Hi everyone,
> I'm wondering how exactly the conditionals are supposed to be used in
> Karaf features:
> 
> 
>    <feature name="example" version="1.2.3">
>      <conditional>
>        <condition>xy</condition>
>        ...
>      </conditional>
>      ...
>    </feature>
> 
> 
> I'm trying to activate a feature (or a list of bundles in that feature)
> only if another feature specified in a condition is already installed.
> 
> I got this working alright, since I install these features dynamically
> with some code anyway, but while it works, I am worried about potential
> side-effects since I don't quite know how it is supposed to be working.
> 
> A simplified pseudo-code version of my code looks like this:
> 
> 
>    // get installed features
>    installedFeatures = featuresService.listInstalledFeatures()
>    // iterate over available features
>    for (Feature feature : featuresService.listFeatures()) {
>      // get all conditions
>      conditions = feature.getConditionals().getConditions()
>      // check if a condition matches an installed feature
>      if (conditions intersect installedFeatures) {
>        // install feature
>        featuresService.installFeature(feature);
>      }
>    }
> 
> 
> Does anyone know if this could have any side-effects?
> 
> Or even better, can anyone give me a proper explanation or
> documentation of how the conditionals in Karaf features work and how
> they are supposed to be used?
> 
> Thanks,
> Lars
>