Expert Spring MVC and Web Flow

You saw the declaration and configuration of this servlet in Chapter 4. To quickly review,

this servlet is configured in your application’s web.xmlfile, as shown in Listing 5-1.

Listing 5-1.DispatcherServlet in the web.xml

<servlet>

<servlet-name>spring</servlet-name>

<servlet-class>

org.springframework.web.servlet.DispatcherServlet

</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>spring</servlet-name>

<url-pattern>/app/*</url-pattern>

</servlet-mapping>

Of course, the URL pattern you choose for the servlet-mappingelement is up to you.

■Tip Many servlet containers will validate the web.xmlagainst its DTD or schema file, so be sure to place

the elements in the right order and in the right place.

Initialization

When the DispatcherServletinitializes, it will search the WebApplicationContextfor one or

more instances of the elements that make up the processing pipeline (such as ViewResolvers

or HandlerMappings).

■Tip Remember that the WebApplicationContextis a special ApplicationContextimplementation

that is aware of the servlet environment and the ServletConfigobject.

For some of the component types such as ViewResolvers (see Table 5-1), the

DispatcherServletcan be configured to locate all instances of the same type. The servlet

will then chain the components together and order them, giving each the chance to handle

the request.

■NoteThe DispatcherServletuses the Orderedinterface to sort many of its collections of delegates.

To order anything that implements the Orderedinterface, simply give it a property named order.The lower

the number, the higher it will rank.

Usually, the first element to respond with a non-null value wins. This is very use-

ful if your application requires different ways to resolve view names, for instance. This

80 CHAPTER 5 ■THE PROCESSING PIPELINE