Session management in gwt

Question

I am using GWT for my client side application. However, I am not sure how I can handle session management. The GWT application resides on one page, all server calls are done via AJAX. If a session expires on the server. let's assume the user didn't close the browser, and sending some request to server using RPC, how could my server notify the application that the session has expired and that the client side portion should show the login screen again?My sample code :

ContactDataServiceAsync contactDataService = GWT
                .create(ContactDataService.class);
        ((ServiceDefTarget) contactDataService).setServiceEntryPoint(GWT
                .getModuleBaseURL()
                + "contactDatas");

        contactDataService.getContact(2,
                new AsyncCallback<ContactData>() {
                    public void onFailure(Throwable caught) {
                                      //code to show error if problem in connection or redirect  to login page

                    }

                    public void onSuccess(ContactData result) {
                        displayContact(result);
                    }
                });

If session expires only it has to show login screen, otherwise it wants to show some error using Window.alert().

How to do this and what are all the codes needed in server side and client side?

Answer 1

You could have the server throw an AuthenticationException to the client in case the user has been logged out.
This will be catched in the callbacks onFailure method, which then can redirect the user to the login-page.

Edit:
AuthenticationException is not a standard exception of course, i was just making an example. It might be best to stick with the standard exceptions.

To try if you caught an specific exception you could use the instanceof operator

    public void onFailure(Throwable e) {
                  if(e instanceof AuthenticationException) {
                        redirecttoLogin();
                  }
                  else {
                    showError(),
               }
            }