handling error messages with spring-boot webflux - spring-boot

Question

i'm writing a java adapter for posting something to a webService.
In the http service i use an ExceptionHandler:
#org.springframework.web.bind.annotation.ExceptionHandler
public ResponseEntity<String> handle(BadCommandException ex) {
return ResponseEntity.badRequest().body(ex.getMessage());
}
That works well, if i call it with curl/postman.
But how can i get the error message that is in the body with a reactive WebClient ?
Part of my client-lib:
private Mono<Optional<String>> post(String bearerToken, Model model, IRI outbox) {
return WebClient.builder()
.build()
.post()
.uri(outbox.stringValue())
.contentType(new MediaType("text","turtle"))
.body(BodyInserters.fromValue(modelToTurtleString(model)))
.header("Authorization", "Bearer " + bearerToken)
.header("profile", "https://www.w3.org/ns/activitystreams")
.accept(new MediaType("text", "turtle"))
.retrieve()
.toEntity(String.class)
.map(res->res.getHeaders().get("Location").stream().findFirst());
}
In success case, i want to return the string from the location header. But how can i for example throw an Exception if the http-status is 400 and add the error message from the body to the exception?
Thanks

Answer 1

the spring documentation on webclient retreive() has examples of how to handle errors. I suggest you start there.
Mono<Person> result = client.get()
.uri("/persons/{id}", id).accept(MediaType.APPLICATION_JSON)
.retrieve()
.onStatus(HttpStatus::is4xxClientError, response -> ...)
.onStatus(HttpStatus::is5xxServerError, response -> ...)
.bodyToMono(Person.class);

Answer 2

.onStatus(HttpStatus::is4xxClientError,
clientResponse -> { return clientResponse.createException();
Javadoc:
/**
* Create a {#link WebClientResponseException} that contains the response
* status, headers, body, and the originating request.
* #return a {#code Mono} with the created exception
* #since 5.2
*/
Mono<WebClientResponseException> createException();
My problem was my testcase 'test bad request'. Because of a refactoring it was sending an empty request body instead of a bad one and the annotation #RequestBody has an attribute 'required' which is default true. So the response body was always empty and did not contain my error message as expected ;-)
public Mono<ResponseEntity<Void>> doIt(Principal principal, #PathVariable String actorId, #RequestBody String model) {
...
that cost me hours ;-)