JIRA pluggin Development - Show alert/notification

JIRA pluggin Development - Show alert/notification

I am currently developing a JIRA plugin of type Workflow post function.
This means I dont have a use for the vm file (velocity template).
I have a java class which extends AbstractJiraFunctionProvider. it
basically calls a web service (asynchronously) using SOAP to update a
remote system on the status of the JIRA issue.
I have got it all working and configured to be triggered when certain JIRA
status transitions are done. What I am trying to do is to show a message
to notify the user if the web service has been called successfully or not.
How do I show a popup message with some text. I tried
JOptionPane.showMessageDialog(null,"Text","Text 2") to my Plugin class But
this doesn't seem to do anything from the plugin java class which extends
AbstractJiraFunctionProvider. Any thoughts or ideas for me to try?