Given a very simple Spring Boot 2.7.3 on Java 17 project with only spring-boot-starter-web as dependency.

If I have this controller:

import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TestRestController {

    @ExceptionHandler
    public void handleException(Exception e) {
        System.out.println("Exception!");
        e.printStackTrace();
    }

    @GetMapping("/")
    public void test() {
        throw new RuntimeException("fake");
    }
}

Then the exception stack trace is printed. However, when I change the @GetMapping to this:

@GetMapping(value = "/", consumes = "application/merge-patch+json")

Then there is a org.springframework.web.HttpMediaTypeNotSupportedException as expected, but the exception handler is not called and no stacktrace is printed.

I also tested with a separate @ControllerAdvice class, but the behavior is the same:

@ControllerAdvice(annotations = RestController.class)
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
public class MyExceptionHandler {
    @ExceptionHandler
    public void handleException(Exception e) {
        System.out.println("Exception in advice!");
        e.printStackTrace();
    }
}

I would like to handle this exception in my error handling library, but I don't know why it never arrives in my exception handler.

Comment From: rstoyanchev

@ExceptionHandler in a controller method applies to exceptions raised when invoking methods of that controller. In this case, however, there is no matching handler. HttpMediaTypeNotSupportedException is raised when no handler fully matches the request, but there is a partial match on the URL and a mismatch in media types that can be consumed.

@ExceptionHandler on an @ControllerAdvice is expected to work and I've confirmed that it does. I suspect there is some difference in your setup, e.g. are you sure that MyExceptionHandler gets registered, given that you have conditions on it?

In general, it is a good idea to provide an actual sample to debug the issue. I'll have to ask for that in this case since I can't reproduce the issue otherwise.

Comment From: wimdeblauwe

I did some more tests. If I change the @ExceptionHandler to not use the annotations argument on @ControllerAdvice anymore, then the handler is called:

@ControllerAdvice
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
public class MyExceptionHandler {
    @ExceptionHandler
    public void handleException(Exception e) {
        System.out.println("Exception in advice!");
        e.printStackTrace();
    }
}

I also tried with @ControllerAdvice(annotations = Controller.class), but then the handler is also not called. Any idea why restricting the advice like that makes it so that the handler is no longer called?

I created a sample project at https://github.com/wimdeblauwe/spring-issue-29120

If you run it and access http://localhost:8080 with a http client, you will see that the custom exception handler is not called. If you comment out the annotations = RestController.class, you will see that it works.

Comment From: rstoyanchev

This comes down once again to the fact there is no matching handler. The ControllerAdvice is set to match @RestController handlers but if there is no matching handler, this criteria cannot be verified. I'm not sure there is much we can do. I realize it looks counter-intuitive in this simple example, but in theory there could be multiple partially matched controller methods.

The only other suggestion I can think of is that you can inject the HandlerMethod associated with the exception into an @ExceptionHandler method and check if that's null in which case at least you know that you're dealing with an exception that occurred before a handler could be selected.

Comment From: wimdeblauwe

I have @ControllerAdvice(annotations = RestController.class) because my error handling library should only be active for @RestController controllers, not for @Controller classes (in case there is a mixed application with a web interface and an API). Is there another way I can have my exception handler only active for rest controllers?

Comment From: rstoyanchev

Your exception handler is already active for @RestController, but in this case where HttpMediaTypeNotSupported is raised before a request is matched to a handler, the condition has to fail if strictly followed. You can choose to handle it unconditionally with a late ordered controller advice perhaps, if that works.