Spring WebClient retrieve json object wrapped under results property

Question

I am currently working on a Spring Boot application wrapping an external REST API into my own GraphQL API.

So far, I've did this method returning a SerieDetails :

public SerieDetails findOrThrow(long id) throws RuntimeException {
        try {
            return this.webClient
                    .get()
                    .uri("/tv/{id}?api_key={apiKey}&language={lang}", id, this.apiKey, this.lang)
                    .retrieve()
                    .bodyToMono(SerieDetails.class)
                    .log()
                    .block();
        } catch(Exception e ) {
            throw new RuntimeException("Can't reach the API");
        }
}

Turning this JSON into my own object :

{
  "id": 71912,
  "name": "The Witcher",
  "overview": "Geralt of Rivia, a mutated monster-hunter for hire, journeys toward his destiny in a turbulent world where people often prove more wicked than beasts."
  "last_air_date": "2019-12-20",
  ...
}

Which works great. But now I am doing another call returning a list of SerieDetails with a given query and it returns the result under the result array :

{
  "page": 1,
  "results": [
      {
        "id": 71912,
        "name": "The Witcher",
        "overview": "Geralt of Rivia, a mutated monster-hunter for hire, journeys toward his destiny in a turbulent world where people often prove more wicked than beasts."
        "first_air_date": "2019-12-20",
        ...
      },
      {
        "id": 106541,
        "name": "The Witcher: Blood Origin",
        "overview": "Set in an elven world 1200 years before the world of The Witcher, the show charts the origins of the very first Witcher, and the events that lead to the pivotal “conjunction of the spheres,” when the worlds of monsters, men, and elves merged to become one.",
        "first_air_date": "2002-09-22",
        ...
      }
  ]
}

And I don't know how to get to it with WebClient. I tried this so far :

public List<SerieDetails> findByQuery(String query) {
        return this.webClient
                .get()
                .uri("/search/tv?api_key={apiKey}&language={lang}&query={query}", this.apiKey, this.lang, query)
                .retrieve()
                .bodyToFlux(SerieDetails.class)
                .log()
                .collect(Collectors.toList())
                .block();
}

But it doesn't work.

Is SerieDetails class the same in both cases?

sigur
– sigur

2021-10-30 22:50:13 +00:00
Commented Oct 30, 2021 at 22:50 — sigur
– sigur, Commented Oct 30, 2021 at 22:50

João Dias · Accepted Answer · 2021-10-30 23:47:06Z

3

You need to change the object to which the JSON is deserialized. The functions bodyToMono and bodyToFlux create two different streams, where Mono and Flux are the publishers:

Mono emits at most one item;
Flux emits a sequence from zero to N items.

The items are the instances of the specified class. In your case, it is the JSON response that is converted to SerieDetails. Multiple items do not mean an array of SerieDetails, but multiple JSON responses with the structure of SerieDetails. You can imagine this like different object instances of the same class.

The simpler solution would be creating the following class:

class PaginatedSerieDetails {
    private int page;
    private List<SerieDetails> results;

    // getters and setters
}

Then you would use this one when you do the call as follows:

public List<SerieDetails> findByQuery(String query) {
        return this.webClient
                .get()
                .uri("/search/tv?api_key={apiKey}&language={lang}&query={query}", this.apiKey, this.lang, query)
                .retrieve()
                .bodyToMono(PaginatedSerieDetails.class)
                .map(PaginatedSerieDetails::getResults())
                .log()
                .block();
}

As a side note, please strive to avoid .block() while using WebFlux. When you do it you defeat the whole purpose of using the reactive stack because you are saying you want to actually make the thread wait for the Mono or Flux to emit a value.

edited Oct 30, 2021 at 23:47

answered Oct 30, 2021 at 22:52

João Dias

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4 Comments

iPPle Over a year ago

Works like a charm thanks ! What can I do as an alternative to .block() then ?

João Dias Over a year ago

Just let the Mono flow to the callers of the findByQuery method. I guess that you have exposed a REST API, everything should be using Mono and Flux. Assuming the call to findByQuery is the result of a call to your own API, you should be returning Mono and Flux in your Controllers. They will be subscribed by Spring and the response is sent to the client whenever it is available. Another very relevant thing to consider is the database. It must support the reactive paradigm so that you can take 100% benefit from it.

Shivam Papat Over a year ago

So is there any way that makes us not create POJO for outer object (which in case here "PaginatedSerieDetails") ?

João Dias Over a year ago

I would say you would need a custom deserializer in that case, but having the class makes it simpler and easier to read.

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