How to use mouse's right click on JTree to pop a menu?

Just add a MouseListener to your JTree, then just check if it's the popup trigger.

You'll need to perform the check in both your mousePressed and mouseReleased methods, as the trigger may differ between platforms (some bring up a menu on the press, others on release.

If it is, just call the show method of your popup menu (I assume you have already created this as an instance variable):

public void mousePressed(MouseEvent e) {
    if (e.isPopupTrigger()) {
        popup.show((Component)e.getSource(), e.getX(), e.getY());
    }
}
public void mouseReleased(MouseEvent e) {
    if (e.isPopupTrigger()) {
        popup.show((Component)e.getSource(),e.getX(), e.getY());
    }
}