Create #extension class in Groovy on Jenkins? - groovy

Question

I'm using the Groovy script screen in jenkins, ie http://localhost:8080/jenkins/script , which is very awesome. I wrote a simple Extension:
jenkins = jenkins.model.Jenkins.getInstance()
#hudson.Extension
public class MyGroovyListener extends hudson.slaves.ComputerListener {
public void onOnline( computer, taskListener ) {
System.out.println("groovy onOnline " + computer + " " + taskListener );
}
}
Now I want to get the extension registered somehow. I tried:
jenkins.refreshExtensions()
... but no joy.
How can I go about registering an extension class from the groovy script webpage?

Answer 1

You need to do a little more to build a Jenkins plugin
You can build them in groovy but it needs to be in a HPI (specialised JAR file) - which you load via the plugin screen. You will need gradle, gent and the example as built by Kiyotaka.
https://github.com/kiy0taka/jenkins-plugin.gent
gent --name=<proj> kiy0taka/jenkins-plugin
cd <proj>
./gradlew server
The gradlew step will run up a local Jenkins server with the plugin ready loaded
There is more as you need to build form components for the configuration and build design step
and also handle serialising config data

Answer 2

This was answered better in the Google Groups post by the same poster, though it may be outdated now. The mentioned issue GROOVY-3361 still exists, and appears to limit how annotations can be processed and scanned for in Groovy classes.
It's a real shame you can't register things against extension points with Groovy code in Jenkins.
I still wonder if it may be possible with a custom hudson.ExtensionFinder, which itself must be written in Java. But I haven't the time to dig that far.