$r.render("sourceview") In the BasicController you will find methods to create easily a modal dialog in your code, but you can also use the DialogBoxControllerFactory. For more information see the org.olat.core.gui.control.generic.modal package.

// define class variable
private DialogBoxController dialogBoxOne;
...
...
// somewhen later, create a dialog and activate it
dialogBoxOne = activateYesNoDialog(ureq, "Hello World",	"Lorem ipsum dolor sit amet...", dialogBoxOne);
...
...
// in the controller event method catch the event and do something
if (source == dialogBoxOne) {
	if (event == Event.CANCELLED_EVENT) {
		feedbackMessage = "close icon clicked";
	} else {
		if (DialogBoxUIFactory.isYesEvent(event)) {
			feedbackMessage = "yes clicked";
		} else {
			feedbackMessage = "no clicked";
		}
	}
}