Request Controller and DispatchServlet
Dispatcher Servlet is used to handle all incoming requests and route them through Spring. When DispatcherServlet receives a web request, it determines which controllers should handle the incoming request.
It first scans for all classes that are declared with the @Controller annotation. The dispatching process depends on the various
@RequestMapping annotations declared in a controller class and its handler methods. There are three levels of request mapping can be defined in Spring controller.