作下记录，WEB.XML的配置及DispatcherServlet-context.xml的配置。

而后者的配置，有不同的形式，不要被迷惑。

WEB.XML

         
      
       DispatcherServlet
          
      
           org.springframework.web.servlet.DispatcherServlet    
           
        
         contextConfigLocation
            
        
             /WEB-INF/spring/webcontext/DispatcherServlet-context.xml    
            
       
      
     
         
      
       DispatcherServlet
          
      
       /
      
     

DispatcherServlet-context.xml

DispatcherServlet-context.xml

The first tag within the <beans> definition is <mvc:annotation-driven />. By this tag,we tell Spring MVC to configure the DefaultAnnotationHandlerMapping,AnnotationMethodHandlerAdapter, and ExceptionHandlerExceptionResolver beans.These beans are required for Spring MVC to dispatch requests to the controllers.

Actually <mvc:annotation-driven /> does many things behind the screen. It also enables support for various convenient annotations such as @NumberFormat and @DateTimeFormat to format the form bean fields during form binding. Similarly, we have the @Valid annotation to validate the controller method’s parameters. It also supports Java objects to/from an XML or JSON conversion via the @RequestBody and @ResponseBody annotations in the @RequestMapping or @ExceptionHandler method during form binding. We will see the usage of these annotations in later chapters. As of now, just remember thatthe <mvc:annotation-driven /> tag is needed to enable annotations such as @controller and @RequestMapping.

What is the purpose of the second tag, <context:component-scan>? You need a bit of background information to understand the purpose of the <context:component-scan> tag. The @Controller annotation indicates that a particular class serves the role of a controller. We already learned that the dispatcher servlet searches such annotated classes for mapped methods (the @RequestMapping annotated methods) to serve a web request. In order to make the controller available for searching, we need to create a bean for this controller in our web application context.

We can create beans for controllers explicitly via the bean configuration (using the <bean> tag—you can see how we created a bean for the InternalResourceViewResolver class using the <bean> tag in the next section), or we can hand over that task to Spring via the autodetection mechanism. To enable the autodetection of the @Controller annotated classes, we need to add component scanning to our configuration using the <context:component-scan> tag. Now, you finally understand the purpose of the <context:component-scan> tag.

Spring will create beans (objects) for every @Controller class at runtime. The dispatcher servlet will search for the correct request mapping method in every @Controller bean based on the @RequestMapping annotation, to serve a web request. The base-package property of a <context:component-scan> tag indicates the package under which Spring should search for controller classes to create beans:

<context:component-scan base-package="com.packt.webstore" />

The preceding line instructs Spring to search for controller classes within the com.packt.webstore package and its subpackages.

Tip

The <context:component-scan> tag not only recognizes controller classes, it also recognizes other stereotypes such as services and repository classes as well. We will learn more about services and repositories later.