Java Reference
In-Depth Information
Following from Figure
5-6
, the high-level overview of the workflow is as follows:
1.
The client sends a request to the web container in the form of an HTTP request.
DispatcherServlet
intercepts the request to figure out the appropriate
handler mappings.
2.
With the help of handler mappings thus figured out, the
DispatcherServlet
dispatches the request to the appropriate controller.
3.
4.
The controller processes the request and returns the model and view objects
to
DispatcherServlet
in the form of a
ModelAndView
instance.
DispatcherServlet
then resolves the
View
(which can be JSP, FreeMarker,
Velocity, and so on) by consulting the
ViewResolver
object.
5.
6. The selected view is then rendered back to the client.
DispatcherServlet
is the heart of Spring Web MVC framework, but before you dive into
DispatcherServlet
, first you must look at
ApplicationContext
in a web application. As mentioned
earlier, a web application has its own specialized
WebApplicationContext
that must be loaded before
DispatcherServlet
is initialized. When the Spring Web MVC application starts and before the web
application is ready to serve the requests, the
WebApplicationContext
and
DispatcherServlet
come
into action, as explained here:
1.
The servlet container initializes the web application and then triggers the
contextInitialized
event, which is listened to by the
ContextLoaderListener
.
ContextLoaderListener
creates the root
WebApplicationContext
.
2.
The
DispatcherServlet
is initialized, creating its own
WebApplicationContext
and nesting it inside the root
WebApplicationContext
.
3.
DispatcherServlet
searches for components such as ViewResolvers and
HandlerMappings. If a component is found, it will be initialized; otherwise, the
default for the component is initialized.
4.
You will look at these steps in greater detail in the sections that follow.
WebApplicationContext
In web applications, the
ApplicationContext
used is called
WebApplicationContext
, and it
is a specialized
ApplicationContext
that is aware of the servlet environment. It is the root
ApplicationContext
in a web application and must be loaded before
DispatcherServlet
initializes
to ensure that all of the services such as the data source are available that are required by the web
application.
WebApplicationContext
is configured in the
web.xml
file using
ContextLoaderListener
,
as illustrated in Listing 5-31.
