Looking for a solution to extend Spring MVC with another Component/Annotation - spring

Question

Suppose I have a Website that is used in normal mode (browser) and in some other mode, like a MobileView mode (inside a mobile app). For each Controller I create, there might be correspondent controller for MobileView, processing the same url.
The easiest solution is to create ifs in all the Controllers that have MobileView logic. Another solution would be to use a correspondent url for MobileView (similar to the normal url) and two separate Controllers (possible where one extends from another; or use some other way to recycle common code)
But, a more elegant solution would be to have some extra annotations, like #SupportsMobileView (to mark a controller, and tell the app that this will have a correspondent MobileView Controller) and #MobileViewController (to mark a second controller, and tell the app that this controller needs to run immediately after the initial controller marked with #SupportsMobileView). The link between a normal controller and a MobileView controller would be through the url they process (defined with #RequestMapping).
Is it possible to extend Spring MVC (A)? Where to inject new annotation scanners (B) and annotation handlers / component handlers (C)? How should the MobileView controller be executed (D) (right now I am thinking that it could be executed through AOP, where the new handler of my new controller type programatically creates a Join-Point on the corresponding normal controller)
Note that I did not mention how this MobileView mode is triggered and detected. Let's just say that there a Session boolean variable (flag) for that.
Critics on any points (A), (B), (C) or (D) are welcomed, as well as technical hints and alternative solution to any point or the whole solution.

Answer 1

HandlerInterceptor can be used to intercept the RequestMapping handling. This is a simple example how to configure and implement one.
You can check for your session variable and will have a bunch of methods that will allow you to do custom processing or just exchange the view from the normal controller handling with your mobile view.

Answer 2

Ok, warnings:
this is only a proof of concept of what I understood must be done so:
+#MobileViewEnable and #MobileView annotated (and related) methods need to stay in the same controller
+there's no check for the httpAction used
+the two methods must have the same signature
+mobileView annotation value and requestMapping annotation value must be equals and uniques
+the logic inside callYourLogic(..) defines which method is going to be called, at the moment there's a very simple logic that check if exist the parameter ("mobile") in the request, just to test
+this code is not intended to be used as is (at all)
+don't know if it works at all outside my pc (joke :D, ehm..)
SO:
Annotations:
#Retention(RetentionPolicy.RUNTIME)
public #interface MobileView {
String value() default "";
}
#Retention(RetentionPolicy.RUNTIME)
public #interface MobileViewEnable {
}
ExampleController:
#Controller
public class MainController extends BaseController {
private final static Logger logger = LoggerFactory.getLogger(MainController.class);
private final static String PROVA_ROUTE = "prova";
#MobileViewEnable
#RequestMapping(PROVA_ROUTE)
public String prova() {
logger.debug("inside prova!!!");
return "provaview";
}
#MobileView(PROVA_ROUTE)
public String prova2() {
logger.debug("inside prova2!!!");
return "prova2view";
}
}
Aspect definition:
<bean id="viewAspect" class="xxx.yyy.ViewAspect" />
<aop:config>
<aop:pointcut expression="#annotation(xxx.yyy.MobileViewEnable)" id="viewAspectPointcut" />
<aop:aspect ref="viewAspect" order="1">
<aop:around method="around" pointcut-ref="viewAspectPointcut" arg-names="viewAspectPointcut"/>
</aop:aspect>
</aop:config>
Aspect implementation:
public class ViewAspect implements BeforeAdvice, ApplicationContextAware {
private final static Logger logger = LoggerFactory.getLogger(ViewAspect.class);
private ApplicationContext applicationContext;
public Object around(ProceedingJoinPoint joinPoint) {
Method mobileViewAnnotatedMethod = null;
HttpServletRequest request = getCurrentHttpRequest();
String controllerName = getSimpleClassNameWithFirstLetterLowercase(joinPoint);
Object[] interceptedMethodArgs = getInterceptedMethodArgs(joinPoint);
String methodName = getCurrentMethodName(joinPoint);
Method[] methods = getAllControllerMethods(joinPoint);
Method interceptedMethod = getInterceptedMethod(methods, methodName);
String interceptedMethodRoute = getRouteFromInterceptedMethod(interceptedMethod);
if (callYourLogic(request)) {
mobileViewAnnotatedMethod = getMobileViewAnnotatedMethodWithRouteName(methods, interceptedMethodRoute);
if (mobileViewAnnotatedMethod != null)
return invokeMethod(mobileViewAnnotatedMethod, interceptedMethodArgs, controllerName);
}
return continueInterceptedMethodExecution(joinPoint, interceptedMethodArgs);
}
private Object continueInterceptedMethodExecution(ProceedingJoinPoint joinPoint, Object[] interceptedMethodArgs) {
try {
return joinPoint.proceed(interceptedMethodArgs);
} catch (Throwable e) {
logger.error("unable to proceed with intercepted method call: " + e);
}
return null;
}
private Object[] getInterceptedMethodArgs(JoinPoint joinPoint) {
return joinPoint.getArgs();
}
private boolean callYourLogic(HttpServletRequest request) {
// INSERT HERE YOUR CUSTOM LOGIC (e.g.: is the server accessed from a mobile device?)
// THIS IS A STUPID LOGIC USED ONLY FOR EXAMPLE
return request.getParameter("mobile")!= null;
}
private HttpServletRequest getCurrentHttpRequest() {
return ((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes()).getRequest();
}
private String invokeMethod(Method method, Object[] methodArgs, String className) {
if (method != null) {
try {
Object classInstance = getInstanceOfClass(method, className);
return (String) method.invoke(classInstance, methodArgs);
} catch (Exception e) {
logger.error("unable to invoke method" + method + " - " + e);
}
}
return null;
}
private Object getInstanceOfClass(Method method, String className) {
return applicationContext.getBean(className);
}
private Method getMobileViewAnnotatedMethodWithRouteName(Method[] methods, String routeName) {
for (Method m : methods) {
MobileView mobileViewAnnotation = m.getAnnotation(MobileView.class);
if (mobileViewAnnotation != null && mobileViewAnnotation.value().equals(routeName))
return m;
}
return null;
}
private String getRouteFromInterceptedMethod(Method method) {
RequestMapping requestMappingAnnotation = method.getAnnotation(RequestMapping.class);
if (requestMappingAnnotation != null)
return requestMappingAnnotation.value()[0];
return null;
}
private String getCurrentMethodName(JoinPoint joinPoint) {
return joinPoint.getSignature().getName();
}
private Method[] getAllControllerMethods(JoinPoint joinPoint) {
return joinPoint.getThis().getClass().getSuperclass().getMethods();
}
private String getSimpleClassNameWithFirstLetterLowercase(JoinPoint joinPoint) {
String simpleClassName = joinPoint.getThis().getClass().getSuperclass().getSimpleName();
return setFirstLetterLowercase(simpleClassName);
}
private String setFirstLetterLowercase(String simpleClassName) {
String firstLetterOfTheString = simpleClassName.substring(0, 1).toLowerCase();
String restOfTheString = simpleClassName.substring(1);
return firstLetterOfTheString + restOfTheString;
}
private Method getInterceptedMethod(Method[] methods, String lookingForMethodName) {
for (Method m : methods)
if (m.getName().equals(lookingForMethodName))
return m;
return null;
}
#Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
}