Sample Chapter 13 - Manning Publications

13.1.1 A day in the life of a request
Getting started with Spring MVC 491
Every time that a user clicks a link or submits a form in their web browser, a
request goes to work. A request’s job description is that of a courier. Just like a
postal carrier or a Federal Express delivery person, a request lives to carry information
from one place to another.
The request is a busy fellow. From the time that it leaves the browser until the
time that it returns a response, it will make several stops, each time dropping off a
bit of information and picking up some more. Figure 13.1 shows all the stops that
the request makes.
When the request leaves the browser, it carries information about what the
user is asking for. At very least, the request will be carrying the requested URL. But
it may also carry additional data such as the information submitted in a form by
the user.
The first stop in the request’s travels is Spring’s DispatcherServlet B. Like
most Java-based MVC frameworks, Spring MVC funnels requests through a single
front controller servlet. A front controller is a common web-application pattern
where a single servlet delegates responsibility for a request to other components
of an application to perform the actual processing. In the case of Spring MVC,
DispatcherServlet is the front controller.
The DispatcherServlet’s job is to send the request on to a Spring MVC controller.
A controller is a Spring component that processes the request. But a typical
application may have several controllers and DispatcherServlet needs help
deciding which controller to send the request to. So, the DispatcherServlet
B
Request Dispatcher
Servlet
C
G
Handler
Mapping
ModelAndView
F
View
D
E
Controller
ViewResolver
Figure 13.1 A request is dispatched by DispatcherServlet to a
controller (which is chosen through a handler mapping). Once the
controller is finished, the request is then sent to a view (which is
chosen through a ViewResolver) to render output.