How to customize SpringWebFlux WebClient JSON dese

Question

I'm using a spring-webflux WebClient (build 20170502.221452-172) to access a Web application producing a stream of Entry objects (application/stream+json) like this:

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 the deserialization of the Entry objects works fine for POJOs using standard common types including Java time (JSR-310) datatypes like java.time.Instant, I wonder what I would have to do in order to add any custom JSON to Java deserialization (e. g., a custom Jackson ObjectMapper).

I can't find any API in WebClient or in the classes of the objects produced by its builder and fluent APIs to do that.

Has anybody used WebClient with customized deserialization?

(Maybe the API is not there, yet?)

Answer 1

Here's an example that customizes the ObjectMapper for JSON (de)serialization. Note that for streaming purposes, different encoders/decoders are being used 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

with 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()

```

Answer 3

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 on 'application level'

by configuring a 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 made effective by the WebClientAutoConfiguration as a WebClient.Builder bean:

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