You don't need to create a full-fledged dice roller application from scratch just to play around with Groovy Dice: why not leverage groovysh and groovyConsole? :-)
The following procedure works for both groovysh and groovyConsole:
groovysh -cp <groovydice-jar> groovyConsole -cp <groovydice-jar>
new net.sf.groovydice.GroovyDice().initialize()
That's it! You are now able to evaluate Groovy Dice expressions in the console. For example:
10.d20.only_if{it.is_even}.view