Global error handling using Spring boot + WebFlux - spring-boot

Question

How can we handle exceptions globally when using reactive programming in Spring boot rest controller?
I would assume that #ControllerAdvice will not work because I have tried this and it was unsuccessful.
My other try is currently this option, using custom attributes:
#Component
public class OsvcErrorAttributes extends DefaultErrorAttributes {
public OsvcErrorAttributes() {
super(true);
}
#Override
public Map<String, Object> getErrorAttributes(ServerRequest request, boolean includeStackTrace) {
return assembleError(request);
}
private Map<String, Object> assembleError(ServerRequest request) {
ServerException serverException = (ServerException)getError(request);
Map<String, Object> errorAttributes = new HashMap<>();
errorAttributes.put("message", serverException.getMessage());
errorAttributes.put("errors", serverException.getErrorMap());
return errorAttributes;
}
}
and WebExceptionHandler like this:
#Component
#Order(-2)
public class OsvcErrorHandler extends AbstractErrorWebExceptionHandler {
public OsvcErrorHandler(ErrorAttributes errorAttributes,
ResourceProperties resourceProperties,
ApplicationContext applicationContext) {
super(errorAttributes, resourceProperties, applicationContext);
// TODO: 25.06.2019 temporary workaround
ServerCodecConfigurer serverCodecConfigurer = new DefaultServerCodecConfigurer();
setMessageWriters(serverCodecConfigurer.getWriters());
setMessageReaders(serverCodecConfigurer.getReaders());
}
#Override
protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {
return RouterFunctions.route(RequestPredicates.all(), this::renderErrorResponse);
}
private Mono<ServerResponse> renderErrorResponse(ServerRequest serverRequest) {
final Map<String, Object> errorAttributes = getErrorAttributes(serverRequest, true);
return ServerResponse.status(HttpStatus.BAD_REQUEST)
.contentType(MediaType.APPLICATION_JSON_UTF8)
.body(BodyInserters.fromObject(errorAttributes));
}
}
Code that generates an error:
#Data
#Service
public class ContactService {
private final ContactRepository contactRepository;
public Mono<Business> saveNewContact(Business business) {
return contactRepository.save(business)
.onErrorMap(throwable ->
ServerException.create(throwable.getMessage())
.persistError("ico", business.getIco(), "ICO is probably duplicate"));
}
}
Problem is that this does not work either. I did follow this tutorial and I cannot see if I am wrong with something or not.

Answer 1

You just use ServerCodecConfigurer injection in you global error handler constructor like this.
public OsvcErrorHandler(GlobalErrorAttributes errorAttributes, ApplicationContext applicationContext,
ServerCodecConfigurer serverCodecConfigurer) {
super(errorAttributes, new ResourceProperties(), applicationContext);
super.setMessageWriters(serverCodecConfigurer.getWriters());
super.setMessageReaders(serverCodecConfigurer.getReaders());
}
Please find the code example in the git repository.

Answer 2

Try injecting the ServerCodecConfigurer instead of instantiating it. I also inject a ViewResolversProvider when doing this, although it might not be necessary.
public OsvcErrorHandler(
final CustomErrorAttributes customAttributes,
final ResourceProperties resourceProperties,
final ObjectProvider<List<ViewResolver>> viewResolversProvider,
final ServerCodecConfigurer serverCodecConfigurer,
final ApplicationContext applicationContext
) {
super(customAttributes, resourceProperties, applicationContext);
this.setViewResolvers(viewResolversProvider.getIfAvailable(Collections::emptyList));
this.setMessageWriters(serverCodecConfigurer.getWriters());
this.setMessageReaders(serverCodecConfigurer.getReaders());
}

Answer 3

You need to define and implement ErrorWebExceptionHandler as a bean and set an #Order annotation with value less than -1, because that is the default of the Spring DefaultErrorWebExceptionHandler
Here is a sample implementation:
public class GlobalErrorHandler extends DefaultErrorWebExceptionHandler {
public GlobalErrorHandler(
final ErrorAttributes errorAttributes,
final WebProperties.Resources resources,
final ErrorProperties errorProperties,
final ApplicationContext applicationContext) {
super(errorAttributes, resources, errorProperties, applicationContext);
}
#Override
public Mono<Void> handle(final ServerWebExchange exchange, final Throwable ex) {
final ServerHttpResponse response = exchange.getResponse();
if (ex instanceof IllegalStateException
&& StringUtils.equals("Session was invalidated", ex.getMessage())
&& response.getStatusCode().is3xxRedirection()) {
final DataBufferFactory bufferFactory = exchange.getResponse().bufferFactory();
return response.writeWith(Mono.just(bufferFactory.wrap("Redirecting...".getBytes())));
}
return super.handle(exchange, ex);
}
}
And here is a sample configuration based on org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration class:
#Configuration
public class ErrorWebFluxAutoConfiguration {
private final ServerProperties serverProperties;
public ErrorWebFluxAutoConfiguration(final ServerProperties serverProperties) {
this.serverProperties = serverProperties;
}
#Bean
#Order(-2)
public ErrorWebExceptionHandler errorWebExceptionHandler(
final ErrorAttributes errorAttributes,
final org.springframework.boot.autoconfigure.web.ResourceProperties resourceProperties,
final WebProperties webProperties,
final ObjectProvider<ViewResolver> viewResolvers,
final ServerCodecConfigurer serverCodecConfigurer,
final ApplicationContext applicationContext) {
final GlobalErrorHandler exceptionHandler =
new GlobalErrorHandler(
errorAttributes,
resourceProperties.hasBeenCustomized()
? resourceProperties
: webProperties.getResources(),
serverProperties.getError(),
applicationContext);
exceptionHandler.setViewResolvers(viewResolvers.orderedStream().collect(Collectors.toList()));
exceptionHandler.setMessageWriters(serverCodecConfigurer.getWriters());
exceptionHandler.setMessageReaders(serverCodecConfigurer.getReaders());
return exceptionHandler;
}
#Bean
#ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
public DefaultErrorAttributes errorAttributes() {
return new DefaultErrorAttributes();
}
}
Thanks to this article which points me to use ErrorWebExceptionHandler.