Cake Solutions Team Blog

So, Spring MVC fans, let’s say you have a @RequestMapping-annotated method in your controller, but you would like to include a custom argument, in addition to the standard ones like Model, HttpServletRequest, and HttpServletResponse.
The solution is to implement a WebArgumentResolver. As an example, we’ll create a CurrentDateWebArgumentResolver; as its name suggests, this resolver will be able to set any Date argument in the controller method to current date.
We have to write

public class ContextExtractingWebArgumentResolver
    implements WebArgumentResolver {

    @Override
    public Object resolveArgument(MethodParameter methodParameter,
        NativeWebRequest webRequest) throws Exception {
        if (Date.class == methodParameter.getParameterType()) {
            return new Date();
        }
        return UNRESOLVED;
    }
}

We then wire-in the argument resolver in our Spring application context configuration file:

<bean class="org.springframework.web.servlet.mvc.annotation.
      AnnotationMethodHandlerAdapter"
    <property name="customArgumentResolver">
        <bean class="package.ContextExtractingWebArgumentResolver"/>
    </property>
</bean>

Once done, we can create a @RequestMapping-annotated method in our controller and include the Date argument; that argument will now receive the current date. For example, we can have

@Controller
public class HomeController {
    @RequestMapping(value="/index", method=RequestMethod.GET)
    public void index(Date date, Model m) {
        m.addAttribute("now", date);
    }
}

The model that will be passed to the view after making a GET request to the /index URL will include attribute named now; the value of the attribute will be the current time.
Naturally, this is just a simple example and injecting current date is not very enterprisey thing to do, but using the approach I have outlined, you can now set much more useful argument types. Do not forget that the implementation of the WebArgumentResolver is a Spring bean, thus having access to all features available in the Spring application context.