Sending request with headers to third parts api with WebClient - spring-boot

Question

I really like the solution I have with RestTemplate but soon it will be depreciated with future spring releases. I am trying to send some text to a third party api using WebClient
String text = URLEncoder.encode(text,"UTF-8");
WebClient webClient = WebClient.builder()
.baseUrl(BASE_URL)
.defaultHeader("Key","af999-e99-4456-b556-4ef9947383d")
.defaultHeader("src", srcLang)
.defaultHeader("tgt", tgtLang)
.defaultHeader("text", text)
.build();
Then send a post here:
Mono<String> response = webClient.post().uri("/google/rtv/text")
.retrieve()
.bodyToMono(String.class);
Trying to parse based off of the legacy response:
private String parseJson( Mono<String> response) {
ObjectMapper mapper = new ObjectMapper();
JsonNode root = null;
JsonNode review = null;
//TODO: create an object and map it here. We need to save the original review too.
try {
root = mapper.readTree(response.toString());
review = root.path("message");
} catch (IOException e) {
e.printStackTrace();
}
return review.asText();
}
Later I need to parse the response but right now I am getting an error saying:
com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'MonoFlatMap': was expecting ('true', 'false' or 'null')
at [Source: (String)"MonoFlatMap"; line: 1, column: 23]
and later:
java.lang.NullPointerException: null
What I am trying to accomplish is something like I have done with RestTemplate.
Like so:
UriComponentsBuilder builder = UriComponentsBuilder
.fromUriString(URL)
.queryParam("src", src)
.queryParam("tgt", tgt)
.queryParam("text", text);
ResponseEntity<String> response = restTemplate.exchange(builder.toUriString(), HttpMethod.GET, request, String.class);
then set my header for the subscription globally.
private ClientHttpResponse intercept(HttpRequest request, byte[] body,
ClientHttpRequestExecution execution) throws IOException {
request.getHeaders().add("Key","af999-e99-4456-b556-4ef9947383d");
ClientHttpResponse response = execution.execute(request, body);
return response;
}
#Bean
public RestTemplate restTemplate() {
RestTemplate restTemplate = new RestTemplate();
restTemplate.setInterceptors(Collections.singletonList(this::intercept));
return restTemplate;
}
Advice?

Answer 1

The problem happens here:
root = mapper.readTree(response.toString());
This code snippet is trying to serialize a Mono<String> as a String, when a Mono is a reactive type that can provide that String value eventually.
You could call response.block() and getting the resulting String, but this would be a blocking call and Reactor forbids that if in the middle of a reactive execution. This is done for good reasons, since this will block one of the few threads that your web application is using and can cause it to stop serving other requests.
You could instead have something like:
Mono<String> review = response.map(r -> parseJson(r);
And then reuse that new value down the line.
Note that WebClient natively supports JSON deserialization and you could deserialize the whole payload like so:
Mono<Review> review = webClient.post().uri("/google/rtv/text")
.retrieve()
.bodyToMono(Review.class);