1. Domino History
2. Interceptors

Interceptors

In some cases we might need to intercept a routing that happening in the application and prevent it based on some logic or needed behavior, for example the user is editing a large form, and he is navigating away from that form before saving his changes, which might be a risky operation, and so we need to show the user a confirmation if he actually meant to navigate out without saving his, or might even ask him to save the changes, then the user can choose between ignoring the message and continue to navigate away without saving or cancel the navigation and save his work before he navigates again.

In domino-history we have the concept of interceptors to help us deal with such use cases, interceptors work in a similar way of java servlets filters, meaning the interceptors in domino-history work in a chain, every interceptor can either cancel the routing or call the next interceptor to continue the chain until one interceptor cancel the routing event or no interceptors remains

			stateHistory.addInterceptor((tokenEvent, chain) -> {
    if(tokenEvent.getParsedToken().hasQueryParameter("editing")
            && Boolean.parseBoolean(tokenEvent.getParsedToken().getQueryParameter("editing").get(0))){
        view.showConfirmation()
                .onOk(()-> chain.next())
                .onCancel(()-> tokenEvent.cancel())
                .showMessage();
    }
});
		

In the above example assuming a view can show a confirmation message, we have our interceptor check if the user is still editing the page and based on his decision we decide to continue or cancel the navigation.

Interceptors in domino-history can be dynamically added or removed to StateHistory instance, this means you can for example add or register an interceptor when a view or page is activated, then when it is deactivated it can be removed, this is helpful when you have a framework that controls your views life-cycle and you dont to keep all interceptors running all the time but instead only for the current activated view, to remove an interceptor we simply use the removeInterceptor method in s StateHistory instance.