How to Resolve Ambiguous @ExceptionHandler for MethodArgumentNotValidException in Spring?

What causes the ambiguous @ExceptionHandler method error in Spring when handling MethodArgumentNotValidException?

@ExceptionHandler({ MethodArgumentNotValidException.class })
@ResponseStatus(HttpStatus.BAD_REQUEST)
@ResponseBody
public ErrorWrapper handleMethodArgumentNotValidException(MethodArgumentNotValidException e) {
    return new ErrorWrapper(".error", "Invalid Argument");
}

The error message 'Ambiguous @ExceptionHandler method mapped for MethodArgumentNotValidException' indicates that there is more than one handler method that can process the exception being thrown. This typically arises from conflicting handler methods defined either in your code or through inherited methods from the parent classes.

@ControllerAdvice
public class RestResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {
    private Logger log = LoggerFactory.getLogger(RestResponseEntityExceptionHandler.class);
    
    @Autowired
    private ApplicationContext applicationContext;
    
    @ExceptionHandler(MethodArgumentNotValidException.class)
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ResponseBody
    public ErrorWrapper handleMethodArgumentNotValidException(MethodArgumentNotValidException e) {
        String fieldName = e.getFieldError().getField();
        String message = getResourceMessage(fieldName + ".error", "Invalid Argument");
        return new ErrorWrapper(fieldName + ".error", message);
    }
    
    private String getResourceMessage(String key, String defaultMessage) {
        String message = applicationContext.getMessage(key, null, Locale.getDefault());
        return StringUtils.isNotEmpty(message) ? message : defaultMessage;
    }
}

Causes

• Multiple @ExceptionHandler methods are defined for the same exception type.
• The handler methods may be inheriting from a parent class that also has an @ExceptionHandler for the same exception.
• Spring is unable to clearly determine which method to invoke due to ambiguity.

Solutions

• Check your entire class hierarchy for inherited exception handlers that may conflict with your own.
• Restrict your @ExceptionHandler to a more specific exception if possible.
• Consider removing the inherited `handleException` method from the `ResponseEntityExceptionHandler` if it is not required.

Mistake: Defining handler methods in a subclass that override parent class methods without paying attention to @ExceptionHandler.

Solution: Ensure that the @ExceptionHandler methods in the subclass are more specific or do not duplicate those in the superclass.

Mistake: Not restricting the exception type in @ExceptionHandler, leading Spring to confuse which handler to call.

Solution: Specify the exact exception class in your @ExceptionHandler annotation.