Global Exception Handling

// Default Spring error — not what clients want to see
{
  "timestamp": "2025-01-01T00:00:00.000+00:00",
  "status": 500,
  "error": "Internal Server Error",
  "path": "/api/v1/orders/99"
}

@RestControllerAdvice
public class GlobalExceptionHandler {

    // Custom error response record
    record ErrorResponse(int status, String error, String message, Instant timestamp) {
        static ErrorResponse of(int status, String error, String message) {
            return new ErrorResponse(status, error, message, Instant.now());
        }
    }

    @ExceptionHandler(ResourceNotFoundException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public ErrorResponse handleNotFound(ResourceNotFoundException ex) {
        return ErrorResponse.of(404, "Not Found", ex.getMessage());
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    public ErrorResponse handleValidation(MethodArgumentNotValidException ex) {
        String message = ex.getBindingResult().getFieldErrors().stream()
            .map(e -> e.getField() + ": " + e.getDefaultMessage())
            .collect(Collectors.joining(", "));
        return ErrorResponse.of(400, "Validation Failed", message);
    }

    @ExceptionHandler(Exception.class)
    @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
    public ErrorResponse handleGeneral(Exception ex, HttpServletRequest req) {
        log.error("Unhandled exception at {}: {}", req.getRequestURI(), ex.getMessage(), ex);
        return ErrorResponse.of(500, "Internal Server Error", "An unexpected error occurred");
    }
}

public class AppException extends RuntimeException {
    private final HttpStatus status;
    public AppException(String message, HttpStatus status) {
        super(message); this.status = status;
    }
    public HttpStatus getStatus() { return status; }
}

public class ResourceNotFoundException extends AppException {
    public ResourceNotFoundException(String resource, String id) {
        super(resource + " not found: " + id, HttpStatus.NOT_FOUND);
    }
}