I was writing a  Spring Boot microservice that called an external service. If the service returned a `500`, the payload of the response had an error code that we wanted to send back to the service that called us. I was using RestTemplate so I thought I could just use:

if (responseEntity.getStatusCode().is2xxSuccessful()){
// happy path
}
if (responseEntity.getStatusCode().is5xxServerError()){
// do the error thing
}

But it’s not that easy. It seems that if the RestTemplate gets anything but a 2xx response, Spring’s default error handler will throw an exception. You won’t even get a chance to do anything with your ResponseEntitybecause the exception happens before that. I even found a recent bug report on the matter. Anyway, I had a chicken and an egg problem – I couldn’t parse the exception out because I didn’t have an entity for it and I didn’t have an entity because the response wasn’t a success. Of course, I may have to accept more status codes than just a 200 or a 500, so I wanted it to be configurable. This old blog entry led me in the right direction of making my own ErrorHandler. What I ended up doing was making an ErrorHandler where I injected the statuses I wanted to make.

I made a simple (and contrived) example on github. It’s actually very simple when you think about it.

My properties file looked like this:

good-status=OK,NOT_ACCEPTABLE

I used the words instead of the error codes. You could obviously change it.

The meat is in the MyResponseErrorHandler class. I injected the property is and then simply tested to see if the error existed:

@Component
public class MyResponseErrorHandler implements ResponseErrorHandler {
    private static final Logger log = LoggerFactory.getLogger(MyResponseErrorHandler.class);
 
    private List acceptableStatus;
 
    public  MyResponseErrorHandler(@Value("${good-status}") String goodStatus) {
 
        acceptableStatus = Arrays.stream(goodStatus.split(","))
                .map(HttpStatus::valueOf)
                .collect(Collectors.toList()) ;
 
 
    }
 
    @Override
    public void handleError(ClientHttpResponse response) throws IOException {
        log.error("Response error: {} {}", response.getStatusCode(), response.getStatusText());
    }
 
    @Override
    public boolean hasError(ClientHttpResponse response) throws IOException {
        return !acceptableStatus.contains(response.getStatusCode());
 
    }
}

And then I just inject the error handler in my client class and use it to construct the RestTemplate

 @Autowired
    public MyConsumerService(RestTemplateBuilder restTemplateBuilder,
                             MyResponseErrorHandler myResponseErrorHandler
                             ) {
 
        this.restTemplate = restTemplateBuilder
                   .errorHandler(myResponseErrorHandler)
                   .build();
    }

And that’s it – I didn’t do anything else.

The bug I referenced above said that this will be easier to do with WebClient in Spring 5. Of course, that means Spring Boot 2 (which, as I write this, is finally on RC1). So I hope that this will help others that are working in Spring Boot 1.5 for a while.