Spring AOP pass String argument of a controller method - spring

Question

I have a controller class with one RequestMapping method which is taking String arguments. I want to pass this argument by using Spring AOP but its failing, I am getting null value when I am printing the value.
Tried with the below provided solution but its working with map but not with String.
Spring AOP pass argument of a controller method
#Controller
public class WelcomeController {
#Autowired
private FamilyService familyService;
#RequestMapping(value = "/", method = RequestMethod.GET)
public ModelAndView welcomePage(String welcomeMessage) {
FamilyVO allFamilyMembers = familyService.getAllFamilyMembers();
ModelAndView modelAndView = new ModelAndView("Index", "family", allFamilyMembers);
List<String> familyMemberAges = new ArrayList<String>();
for (int i = 0; i <= 100; i++) {
familyMemberAges.add("" + i);
}
modelAndView.addObject("familyMemberAges", familyMemberAges);
System.out.println(welcomeMessage);
return modelAndView;
}
}
#Component
#Aspect
public class WelcomeControllerAspect {
#Before("execution(* com.kalavakuri.webmvc.web.controller.WelcomeController.welcomePage(..))")
public void beforeWelcomePage(JoinPoint joinPoint) {
joinPoint.getArgs()[0] = "Hellow";
System.out.println(joinPoint.getArgs().length);
System.out.println("Before welcomepage");
}
}
I am expecting the value "Hello" when I print it in Controller class but printing null.

Answer 1

A #Before advice is not meant to manipulate method parameters. In the example you linked to it only works because the argument is a mutable object, namely a Map. A String is immutable, though, you cannot edit it.
Having said that, what should you do? Use an #Around advice which was designed for that kind of thing. There you can decide how you want to proceed, e.g.
call the original method with original parameters,
call the original method with changed parameters,
do something before and/or after calling the original,
don't call the original method but return another result instead,
handle exceptions in the original method
or any mix of the above which makes sense (maybe you have multiple cases and if-else or switch-case).
I also suggest not to work directly on the Object[] of JoinPoint.getArgs() but to bind the relevant method parameter(s) to a named and type-safe advice parameter via args(). Try this:
package de.scrum_master.aspect;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.springframework.stereotype.Component;
#Component
#Aspect
public class WelcomeControllerAspect {
#Around(
"execution(* com.kalavakuri.webmvc.web.controller.WelcomeController.welcomePage(..)) && " +
"args(welcomeMessage)"
)
public Object beforeWelcomePage(ProceedingJoinPoint joinPoint, String welcomeMessage) throws Throwable {
System.out.println(joinPoint + " -> " + welcomeMessage);
return joinPoint.proceed(new Object[] { "Hello AOP!" });
}
}

Answer 2

You should use an #Around advice instead of a #Before.
See this answer for more details.