Getting a Controller Method Name in a Spring Filter: Unraveling the Mystery

As a developer, you’ve probably encountered situations where you need to access the controller method name in a Spring filter. Maybe you want to log the method name for auditing purposes, or perhaps you need to perform some custom logic based on the method name. Whatever the reason, getting the controller method name in a Spring filter can be a bit of a challenge. But fear not, dear reader, for we’re about to dive into the solution!

The Problem: Why Can’t I Get the Controller Method Name?

One of the main reasons you can’t get the controller method name directly in a Spring filter is because the filter is executed before the dispatcher servlet, which is responsible for mapping the request to the controller method. This means that when the filter is executed, the controller method hasn’t been invoked yet, and therefore, the method name is not available.

Another reason is that the `HttpServletRequest` object, which is passed to the filter, doesn’t contain any information about the controller method name. You can try accessing the request attributes, headers, or parameters, but you won’t find the method name anywhere.

The Solution: Using Aspect-Oriented Programming (AOP)

One way to get the controller method name in a Spring filter is by using Aspect-Oriented Programming (AOP). AOP is a programming paradigm that allows you to modularize cross-cutting concerns, such as logging, security, or caching, and apply them to your application in a declarative way.

In our case, we can use AOP to create an aspect that intercepts the controller method invocation and extracts the method name. We’ll then store the method name in a thread-local variable, which can be accessed in the filter.

Step 1: Create an Aspect

Create a new Java class that will serve as our aspect:

@Aspect
public class ControllerMethodAspect {
    
    @Around("execution(* *(..))")
    public Object around(ProceedingJoinPoint joinPoint) throws Throwable {
        String methodName = joinPoint.getSignature().getMethod().getName();
        MethodHolder.setMethodName(methodName);
        return joinPoint.proceed();
    }
}


This aspect uses the `@Around` annotation to define an advice that will be executed around the controller method invocation. The `execution(* *(..))` pointcut expression matches any method execution, and the `around` method extracts the method name using the `getSignature()` method.
Step 2: Create a Thread-Local Variable Holder
Create a new Java class that will hold the thread-local variable:

public class MethodHolder {
    
    private static final ThreadLocal<String> methodNameHolder = new ThreadLocal<>();
    
    public static void setMethodName(String methodName) {
        methodNameHolder.set(methodName);
    }
    
    public static String getMethodName() {
        return methodNameHolder.get();
    }
}


This class uses a thread-local variable to store the method name.
Step 3: Configure the Aspect
Add the aspect to your Spring configuration file:

<beans>
    <aop:aspectj-autoproxy />
    <bean id="controllerMethodAspect" class="com.example.ControllerMethodAspect" />
</beans>


This configuration enables aspect autoproxying and registers the aspect bean.
Accessing the Method Name in the Filter
Now that we have the aspect and thread-local variable in place, we can access the method name in our filter:

public class MyFilter implements Filter {
    
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        String methodName = MethodHolder.getMethodName();
        // Log the method name or perform custom logic
        chain.doFilter(request, response);
    }
}


In this example, we access the thread-local variable in the filter to get the method name.
Alternative Solution: Using a Request Attribute
Another way to get the controller method name in a Spring filter is by using a request attribute. We can create a custom `HandlerMethodArgumentResolver` that sets a request attribute with the method name:

public class MethodNameResolver implements HandlerMethodArgumentResolver {
    
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return false;
    }
    
    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        String methodName = parameter.getMethod().getName();
        webRequest.setAttribute("methodName", methodName, RequestAttributes.SCOPE_REQUEST);
        return null;
    }
}


This resolver sets a request attribute named `methodName` with the method name.
Add the resolver to your Spring configuration file:

<mvc:annotation-driven>
    <mvc:argument-resolvers>
        <bean class="com.example.MethodNameResolver" />
    </mvc:argument-resolvers>
</mvc:annotation-driven>


Now, we can access the method name in our filter:

public class MyFilter implements Filter {
    
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        String methodName = (String) httpRequest.getAttribute("methodName");
        // Log the method name or perform custom logic
        chain.doFilter(request, response);
    }
}


In this example, we access the request attribute to get the method name.
Conclusion
In this article, we've explored two solutions for getting the controller method name in a Spring filter. The first solution uses Aspect-Oriented Programming (AOP) to intercept the controller method invocation and extract the method name, while the second solution uses a custom `HandlerMethodArgumentResolver` to set a request attribute with the method name.
Both solutions provide a way to access the controller method name in a filter, allowing you to perform custom logic or logging based on the method name. Choose the solution that best fits your needs, and happy coding!

Remember to choose the solution that best fits your needs, and don't hesitate to reach out if you have any questions or need further clarification!

• Spring AOP Documentation
• Spring MVC Argument Resolvers Documentation

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