AFAIK The JNLP API is available only if you launch your application using java web start (JWS) technology: read more here: http://java.com/en/download/faq/java_webstart.xml
If that is an option for you, oracle has some example of how to use the SingleInstanceService here
Implement and Register SingleInstanceListener. It will be invoked with the main-args when new instances of your application is launched.