How to catch browser Refresh event

I have this code that suppose to logout user when he closes tab or browser. But event happened also when user presses “Refresh” button. How do I know that this is refresh and not really close event?

                  Window.addWindowClosingHandler(new Window.ClosingHandler() {

                        @Override

                        public void onWindowClosing(ClosingEvent event) {

                              logout();

                        }

                       

                  });

I am in development mode now using Firefox 9.0.1

-Sergey

 

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