Global unntakshåndtering med @ControllerAdvice

@RestControllerAdvice
public class GlobalExceptionHandler {
    // @ExceptionHandler methods go here
}

@ExceptionHandler(ResourceNotFoundException.class)
public ResponseEntity<ErrorResponse> handleNotFound(ResourceNotFoundException ex) {
    return ResponseEntity.status(HttpStatus.NOT_FOUND)
        .body(new ErrorResponse("NOT_FOUND", ex.getMessage()));
}

@ExceptionHandler({IllegalArgumentException.class, IllegalStateException.class})
public ResponseEntity<ErrorResponse> handleBadRequest(RuntimeException ex) {
    return ResponseEntity.badRequest()
        .body(new ErrorResponse("BAD_REQUEST", ex.getMessage()));
}

@ExceptionHandler(MethodArgumentNotValidException.class)
public ResponseEntity<Map<String, Object>> handleValidation(MethodArgumentNotValidException ex) {
    Map<String, String> fieldErrors = new LinkedHashMap<>();
    ex.getBindingResult().getFieldErrors().forEach(e ->
        fieldErrors.put(e.getField(), e.getDefaultMessage()));
    return ResponseEntity.badRequest()
        .body(Map.of("errors", fieldErrors, "status", 400));
}

@ExceptionHandler(ConstraintViolationException.class)
public ResponseEntity<Map<String, String>> handleConstraint(ConstraintViolationException ex) {
    Map<String, String> errors = new LinkedHashMap<>();
    ex.getConstraintViolations().forEach(v ->
        errors.put(v.getPropertyPath().toString(), v.getMessage()));
    return ResponseEntity.badRequest().body(errors);
}

@ExceptionHandler(Exception.class)
public ResponseEntity<ErrorResponse> handleAll(Exception ex, HttpServletRequest req) {
    log.error("Unhandled error on {} {}", req.getMethod(), req.getRequestURI(), ex);
    return ResponseEntity.internalServerError()
        .body(new ErrorResponse("INTERNAL_ERROR", "Unexpected error"));
}

@ResponseStatus(HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException {
    public ResourceNotFoundException(String msg) { super(msg); }
}

@RestControllerAdvice(basePackages = "com.example.api")
public class ApiExceptionHandler { ... }
@RestControllerAdvice(assignableTypes = {UserController.class, OrderController.class})
public class SpecificHandler { ... }

@ExceptionHandler(Exception.class)
public ResponseEntity<ErrorResponse> handleAll(Exception ex, HttpServletRequest req) {
    if (ex instanceof BusinessException) log.warn("Business error: {}", ex.getMessage());
    else log.error("Unexpected error on {}", req.getRequestURI(), ex);
    return ...
}