How to configure JSON deserialization of SpringWebFlux WebClient?

Question

I am using spring -webflux WebClient (build 20170502.221452-172) to access a web application creating an input stream of objects (application / stream + json):

final WebClient producerClient = WebClient.create("http://localhost:8080/");

Flux<Entry> entries = producerClient.get().uri("json-stream")
        .accept(MediaType.APPLICATION_STREAM_JSON)
        .exchange()
        .flatMapMany(clientResponse -> clientResponse.bodyToFlux(Entry.class));

While deserializing Entry objects works fine for POJOs using standard common types, including Java time types (JSR-310) like java.time.Instant, I wonder what I need to do to add any custom JSON to Deserialization Java (for example, a custom ObjectMapper).

I can’t find any API in WebClient or in classes of objects created by its creator and freely used APIs that.

Has anyone used WebClient with custom deserialization?

(Maybe the API is not there yet?)

Answer 1

Here is an example that sets up serialization ObjectMapperfor JSON (de). Please note that different encoders / decoders are used for streaming, but the principle remains the same for their configuration.

    ExchangeStrategies strategies = ExchangeStrategies
            .builder()
            .codecs(clientDefaultCodecsConfigurer -> {
                clientDefaultCodecsConfigurer.defaultCodecs().jackson2JsonEncoder(new Jackson2JsonEncoder(new ObjectMapper(), MediaType.APPLICATION_JSON));
                clientDefaultCodecsConfigurer.defaultCodecs().jackson2JsonDecoder(new Jackson2JsonDecoder(new ObjectMapper(), MediaType.APPLICATION_JSON));

            }).build();

    WebClient webClient = WebClient.builder().exchangeStrategies(strategies).build();

Answer 2

You can configure this for a specific WebClient:

@Autowired
public ItunesAlbumServiceImpl(ObjectMapper mapper) {
    ExchangeStrategies strategies = ExchangeStrategies.builder().codecs(clientCodecConfigurer ->
        clientCodecConfigurer.customCodecs().decoder(
                new Jackson2JsonDecoder(mapper,
                        new MimeType("text", "javascript", StandardCharsets.UTF_8)))
    ).build();

    webClient = WebClient.builder()
            .exchangeStrategies(strategies)
            .baseUrl("https://itunes.apple.com")
            .build();
}

But also at the application level

setting up CodecCustomizer:

@Bean
public CodecCustomizer jacksonLegacyJsonCustomizer(ObjectMapper mapper) {
    return (configurer) -> {
        MimeType textJavascript = new MimeType("text", "javascript", StandardCharsets.UTF_8);
        CodecConfigurer.CustomCodecs customCodecs = configurer.customCodecs();
        customCodecs.decoder(
                new Jackson2JsonDecoder(mapper, textJavascript));
        customCodecs.encoder(
                new Jackson2JsonEncoder(mapper, textJavascript));
    };
}

which will be effective using WebClientAutoConfigurationas a WebClient.Builderbean:

@Autowired
public ItunesAlbumServiceImpl(WebClient.Builder webclientBuilder) {
    webClient = webclientBuilder.baseUrl("https://itunes.apple.com").build();
}

Answer 3

webflux 5.0.2, de-registerDefaults `` `

val strategies = ExchangeStrategies.builder()
                .codecs { configurer ->
                    configurer.registerDefaults(false)
                    configurer.customCodecs().encoder(Jackson2JsonEncoder(objectMapper, APPLICATION_JSON))
                    configurer.customCodecs().decoder(Jackson2JsonDecoder(objectMapper, APPLICATION_JSON))
                }.build()

`` `