Problem with transactionStart

Hi,

I’m developing a Vaadin portlet for Liferay. Trying to get URL parameter:


public class DsinfoApplication extends Application implements TransactionListener{
	
	@Override
	public void transactionStart(Application application, Object transactionData) {
		if(application == DsinfoApplication.this)
		{
			System.out.println("start");
			RenderRequest req = (RenderRequest) transactionData;
			HttpServletRequest httpReq = PortalUtil.getHttpServletRequest(req);
			HttpServletRequest origin = PortalUtil.getOriginalServletRequest(httpReq);
			String param = origin.getParameter("dissId");
			System.out.println("Parameter dissId="+param);
		}
	}


	@Override
	public void transactionEnd(Application application, Object transactionData) {
		// TODO Auto-generated method stub
		System.out.println("end");
		
	}
	
	public void init() {
	       getContext().addTransactionListener(this);
    	       Window window = new Window("kgkgh");
        
        setMainWindow(window);
    }
	
}

I got a parameter right way, but also i am getting an internal error in portal.
transactionStart(Application, Object) method is invoked again:


start
Parameter dissId=1
end
start

Could anybody explain me such a behaviour?

Thanks in advance!