Intercepting controllers in Spring MVC

Working on my latest project the past couple days I was trying to figure out a way to enforce authentication for some requests but not others. I first wrote a Filter but when I started mapping the filter to my specific URLs I realized how tedious this could become. I then remembered that Spring allowed for interceptors in its web framework and after a quick glance through their documentation I found the section I was looking for. Unfortunately this still wasn’t exactly what I needed as Spring applies your interceptors to all requests configured in your handler mapping. Looking at the HandlerInterceptor API I found I had access to the handler that was being processed and I just needed to decorate my handlers that needed authentication and adjust my interceptor to first check the handler. I decided to create an empty Interface named AuthenticatedController which my controllers could implement to indicate they needed to be protected from unauthenticated access. You could also do this using annotations, but here’s my code:

AuthenticatedController.java

public interface AuthenticatedController {
    // This is empty on purpose.
}

SimpleController.java

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ModelAndView;

public class StateController implements AuthenticatedController {

    public ModelAndView handleRequest( final HttpServletRequest httpServletRequest,
            final HttpServletResponse httpServletResponse ) throws Exception {
        ...
    }

}

AuthenticationInterceptor.java

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class AuthenticationInterceptor extends HandlerInterceptorAdapter {

    public boolean preHandle( HttpServletRequest request, HttpServletResponse response,
            Object handler ) throws Exception {

        if ( !( handler instanceof AuthenticatedController ) ) {
            // Authentication not needed, allow request to continue.
            return true;
        }

        boolean isAuthenticated = checkAuthentication(...);

        if ( !isAuthenticated ) {
            // User is not authenticated, handle response as needed, and halt processing.
            response.setStatus( HttpServletResponse.SC_FORBIDDEN );
            return false;
        }

        // User is authenticated, allow request to continue.
        return true;
    }
}

spring-beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

<bean name="authenticationInterceptor" class="custom.AuthenticationInterceptor" />

<bean name="urlMapping"
    class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
    <property name="interceptors">
         <list>
       <ref bean="authenticationInterceptor" />
  </list>
    </property>
    <property name="mappings">
  <props>
            <prop key="/controller1.json">controller1</prop>
            <prop key="/controller2.json">controller2</prop>
            <prop key="/controller3.json">controller3</prop>
        </props>
    </property>
</bean>

</beans>

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Intercepting Controllers in Spring MVC

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