Unable to set values in the map using webclient call response - reactive-programming

Question

I am unable to get values filled in the map after making a web client call and using the response of the previous Mono.Here is the code I have tried.The value of parameters.size() comes out to zero.Not able to get the reason as to why the value is not filled.I basically want to return age ( and not Mono object)
from this method.Using block gives an error block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-3.
Map<String, String> parameters = new HashMap<String,String>();
Mono<Person> obj = webClient
.post()
.uri("dummy url")
.accept(MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML)
.retrieve()
.bodyToMono(Person.class)
.flatMap(resp -> {
parameters.put("name", resp.getName());
parameters.put("age", resp.getAge());
return Mono.just(new Person(resp.getName(),resp.getAge()));
}
);
System.out.println(parameters.size());
Please suggest where I am wrong and solution to fix the same.

Answer 1

Since this is about collecting and using a token of some sort collected from a previous HTTP call, your best bet is to delegate all that to an ExchangeFilterFunction.
An ExchangeFilterFunction is a filter that is executed on the client side for each outgoing request. Here is a very, very naïve implementation of such a filter:
class TokenFilterFunction implements ExchangeFilterFunction {
private final AtomicReference<String> token = new AtomicReference<>();
#Override
public Mono<ClientResponse> filter(ClientRequest req, ExchangeFunction next) {
if (this.token.get() == null) {
return fetchToken(next).then(sendRequest(req, next));
}
else {
return sendRequest(req, next);
}
}
private Mono<ClientResponse> sendRequest(ClientRequest req, ExchangeFunction next) {
ClientRequest request = ClientRequest.from(req)
.header("Token", this.token.get()).build();
return next.exchange(request);
}
private Mono<Void> fetchToken(ExchangeFunction next) {
ClientRequest tokenRequest = ClientRequest.create(HttpMethod.GET,
URI.create("https://example.com/token")).build();
return next.exchange(tokenRequest).doOnNext(res -> {
this.token.set(res.headers().header("Token").get(0));
}).then();
}
}
This could automatically call the token endpoint to fetch a token when needed and directly chain with the request you asked in the first place. Again, such an implementation should be much more complex than that, handling domains, errors, and more.
If you're using some authentication technology, such a filter might be implemented already in Spring Security in a much, much better way.
You can configure it on your client during the building phase, like:
WebClient webClient = WebClient.builder().filter(new TokenFilterFunction()).build();