How to customize the internal server error message (error code : 500)

Consider a scenario where I want to create a record in database with the already existing ID. By doing this, we get “500-internal server error”. But I want to customize the message returned to “Id already exist, Cannot create record”. Below is the my sample existing code: Controller class :

    @PostMapping(value = "/plans")
    public ResponseEntity<ResponseSave> savePostPlanDetails(
            @Valid @RequestBody(required = true) Plan plan) throws ParseException {

        String planId = plan.getPlanId();

        Integer createdId = planDataService.savePlan(plan, planId);

        ServiceMessage serviceMessage = ServiceMessage.createCreatedServiceMessage();
        return new ResponseEntity<>(ResponseSave.createResponseSave(serviceMessage, createdId), HttpStatus.CREATED);
    }

Service class :

public Integer savePlan(Plan plan, String planId) throws ParseException {


        PlanDao findResponse = planDataRepository.findByPlanId(planId);

        if (findResponse != null) {
            //This line generate 500 error if create with already existing ID.
            throw new IllegalArgumentException(PlanSearchEnum.RECORD_ALREADY_EXIST.getValue());                                                                                                 
        }
        
        PlanDao planDao1 = requestToResponseMapper.panToPlanDao(plan);
        PlanDao saveResponse = planDataRepository.save(planDao1);
        return saveResponse.getInternalId();

    }

Postman Output :

{
    "message": {
        "code": "500",
        "description": "Unable to process request",
        "type": "Internal Server Error"
    }
}

As in the above postman response, I want the description to be like : “description”: “Id already exist, Cannot create record” instead of the general message as show above. So how to do this ?

Answer

You will need to have a handler for the exception:

@ControllerAdvice
@Slf4j
public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {

    @ExceptionHandler(value = {IllegalArgumentException.class})
    public ResponseEntity<Object> handleIllegalArgumentExceptions(Exception exception, WebRequest webRequest) {
        HttpStatus errorCode = HttpStatus.INTERNAL_SERVER_ERROR;

        return this.handleExceptionInternal(exception, new ErrorInfo(errorCode.value(), "Id already exist, Cannot create record"), new HttpHeaders(), errorCode, webRequest);
    }
}

And the model ErrorInfo:

public class ErrorInfo {
    private final int code;
    private final String description;
}

Finally, you should definitely consider creating your own exception instead of using the generic IllegalArgumentException. You can create something more meaningful for your business case, such as RecordAlreadyExistsException.