Re: Usage of conditional in Karaf features

[Jean-Baptiste Onofré]

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