Expert Spring MVC and Web Flow

Summary

The ThrowawayControlleris an alternate request handling method compared to the

Controllers we’ve seen so far. It is intended to encapsulate both the request parameters as

well as the behavior associated with the request. A new ThrowawayControlleris created for

each request, so it must be a prototype bean (by specifying singleton="false"in the bean

definition).

Request parameters are bound directly to the controller, and if there are no data binding

errors, the controller’s execute()method is called to handle the request.

ValidatableThrowawayController

The standard ThrowawayControllercan’t support any fine grained data binding configuration

because there is no callback to specify any custom PropertyEditors. If there are any data bind-

ing errors, the controller never knows about them, making proper error handling cumbersome.

Enter the ValidatableThrowawayController, as shown in Listing 6-77, which adds a bit

more complexity but fills in the gaps of error handling. This controller type is still a stateless

Command pattern implementation of a controller, so you should use it wherever you would

use a ThrowawayControllerbut require the ability to register custom PropertyEditors or build

work flows that take into account any errors.

Listing 6-77.ValidatableThrowawayController

public interface ValidatableThrowawayController {

String getName();

void initBinder(DataBinder binder) throws Exception;

ModelAndView execute(BindException errors) throws Exception;

}

If you wish to use this controller, you must also declare a ValidatableThrowaway➥

ControllerHandlerAdapterin your WebApplicationContext. If you do, be sure to also include

any other handler adapters, as the defaults are only included if no handler adapter is found in

the ApplicationContext.

HandlerInterceptors

The Servlet 2.3 specification introduced the idea of filters, common code that can wrap one or

more servlets to provide pre- and post-processing of the request and response. Spring MVC

supports an analogous concept with its HandlerInterceptors, which wrap request handlers to

provide common functionality. Interceptors handle more life cycle events than a standard fil-

ter, but filters are more powerful, in that they may directly manipulate or replace the

HttpServletRequestand HttpServletResponseobjects.

Listing 6-78 contains the HandlerInterceptorinterface.

196 CHAPTER 6 ■THE CONTROLLER MENAGERIE