Expert Spring MVC and Web Flow

Summary

Mapping incoming requests to request handlers is very flexible in Spring MVC. Out of the box,

URL mapping methods are provided, but it’s very easy to create mapping strategies that use

any information available in the HttpServletRequest.

The BeanNameUrlHandlerMappingis the default mapping strategy and is used if no other

mapping strategies are defined in the ApplicationContext. This strategy, while simple and

easy, does have a few limitations. If you require complex interceptor mapping or the use of

prototype beans for handlers, you will need to use the SimpleUrlHandlerMapping.

Handler mapping strategies can be ordered using the Orderedinterface, allowing you to

utilize multiple methods to resolve incoming requests to handlers.

HandlerExceptionResolver

When an exception occurs from handling a request, Spring MVC can catch the exception for

you and route the request to a particular error page or other exception handling code. The

HandlerExceptionResolverwill handle any exception thrown inside the HandlerInterceptors,

the Controllers, or the Viewrendering. Typically, an exception is mapped to a particular error

page, but it is easy to extend this functionality for your particular error handling needs.

By using a HandlerExceptionResolver, shown in Listing 5-18, it is easy to centralize error

handling and configuration. Otherwise, each controller and interceptor would have to contain

duplicate code and logic for each exception that could be thrown.

Listing 5-18.HandlerExceptionResolver Interface

package org.springframework.web.servlet;

public interface HandlerExceptionResolver {

ModelAndView resolveException(

HttpServletRequest request, HttpServletResponse response,

Object handler, Exception ex);

}

The DispatcherServletis configured by default to look for all beans in its

ApplicationContextof type HandlerExceptionResolver. If it finds one or more, it will order

them using the org.springframework.core.Orderedinterface if the bean implements it. If

no HandlerExceptionResolveris found, no exception resolving will take place. Of course, any

mapped exceptions you have specified in the web.xmlwill still apply if the exception isn’t han-

dled by a HandlerExceptionResolver.

You may also tell the DispatcherServletto use only a single exception resolver,

ignoring all others that may be present in the ApplicationContext. Simply set the

detectAllHandlerExceptionResolversproperty of the DispatcherServletto false,

and then define a single bean with the name handlerExceptionResolver.

94 CHAPTER 5 ■THE PROCESSING PIPELINE