How to customize SpringWebFlux WebClient JSON deserialization?

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?)

score 70 · Answer 1 · edited Jan 26 '18 at 00:27

70

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();

edited Jan 26 '18 at 00:27

Chris

3,437
6
40
73

answered May 16 '17 at 09:07

Brian Clozel

56,583
15
167
176

7

Could you tell the reason why Jackson2ObjectMapperBuilderCustomizer is not applied to default codecs? – hahn Sep 20 '17 at 19:04
This sounds like a new question to me - could you create one? – Brian Clozel Sep 20 '17 at 19:12
11

@hahn If you use the preconfigured WebClient.Builder provided by spring instead of Webclient.builder(), you can get the objectMapper customizations done automatically Ref: https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html#boot-features-webclient – Sai Surya Kattamuri May 26 '20 at 01:47

score 13 · Answer 2 · edited Nov 05 '20 at 13:42

Based on the replies above, I ended up with this code:

final ObjectMapper mapper = new ObjectMapper()
    .findAndRegisterModules()
    .enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
final ExchangeStrategies exchangeStrategies = ExchangeStrategies.builder()
    .codecs(configurer -> configurer.defaultCodecs()
    .jackson2JsonDecoder(new Jackson2JsonDecoder(mapper)))
    .build();
final WebClient webClient = WebClient.builder()
    .exchangeStrategies(exchangeStrategies)
    .build();

If you don't include .findAndRegisterModules(), you're going to have problems when you want to deserialise things like Java 8's time objects.

score 10 · Answer 3 · answered Aug 16 '17 at 15:06

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();
}

score 8 · Answer 4 · answered Apr 15 '20 at 12:50

Configuring globally:

@Configuration
public class AppConfig {

    private final ObjectMapper objectMapper;

    @Autowired
    public AppConfig(ObjectMapper objectMapper) {
        this.objectMapper = objectMapper;
        this.webClientBuilder = WebClient.builder()
                .exchangeStrategies(exchangeStrategies());
    }

    private ExchangeStrategies exchangeStrategies() {
        Jackson2JsonEncoder encoder = new Jackson2JsonEncoder(objectMapper);
        Jackson2JsonDecoder decoder = new Jackson2JsonDecoder(objectMapper);
        return ExchangeStrategies
                .builder()
                .codecs(configurer -> {
                    configurer.defaultCodecs().jackson2JsonEncoder(encoder);
                    configurer.defaultCodecs().jackson2JsonDecoder(decoder);
                }).build();
    }
}

score 6 · Answer 5 · answered May 18 '20 at 10:02

6

Since Spring 5.1.13 you can use a dedicated .codec method to customize them:

WebClient.builder()
    .codecs(configurer -> {
        configurer.defaultCodecs().jackson2JsonEncoder(new Jackson2JsonEncoder(new ObjectMapper(), MediaType.APPLICATION_JSON));
        configurer.defaultCodecs().jackson2JsonDecoder(new Jackson2JsonDecoder(new ObjectMapper(), MediaType.APPLICATION_JSON));
     })
    .build();

answered May 18 '20 at 10:02

tomasulo

1,252
8
9

Thanks for this - I should really update the question with code for more recent Spring versions... – Martin May 18 '20 at 14:17

Amit Yatagiri · Answer 6 · 2020-03-10T16:55:37.123

5

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()

edited Mar 10 '20 at 16:55

answered Jan 25 '18 at 16:31

Amit Yatagiri

425
1
4
16

this question is tagged `Java` and not `Kotlin` – Stefan Haberl Apr 01 '20 at 15:27

score 1 · Answer 7 · answered Jun 27 '23 at 11:01

If anyone interested in customizing the WebTestClient during a test, then it would be a similar approach. Just need to mutate the original bean.

@Autowired
private WebTestClient webTestClient;

@Test
void test() {
    webTestClient.mutate()
        .codecs(clientCodecConfigurer -> clientCodecConfigurer.defaultCodecs()
            .jackson2JsonDecoder(new Jackson2JsonDecoder(CUSTOM_OBJECT_MAPPER, MediaType.APPLICATION_JSON)))
        .build()
        .get()
        .uri("/test-endpoint")
        .exchange()
        .expectStatus().isOk();

score 0 · Answer 8 · answered Jul 24 '23 at 09:05

In case you use Spring Boot then you can use auto-configured ObjectMapper and omit verbose codecs configuration. Just define bean like this:

@Bean
public WebClient webClient(WebClient.Builder builder) {
    return builder.build();
}

As I explained here Spring Boot does auto-configure WebClient builder. When you create instance by hand it uses built-in defaults and then you have to manually update codecs using one of methods above.

score 0 · Answer 9 · answered Jul 25 '23 at 17:36

The most direct, concise, and surgical way I've found, which I read about in in Baeldung's Spring Boot: Customize the Jackson ObjectMapper, is to use a Jackson2ObjectMapperBuilderCustomizer. It looks like this:

@Configuration
public class MyAppConfiguration {

  @Bean
  public Jackson2ObjectMapperBuilderCustomizer jacksonJsonCustomizer() {
    return builder -> builder.modulesToInstall(/*TODO specify modules here);
  }

}

I've verified that this works with Spring Data as well as WebFlux, e.g. WebClient and .bodyToMono(SomeType.class). It even works in conjunction with WebClientCustomizer if you happen to be using that for customizing the WebClient; see the answers to Spring WebClient.Builder timeout defaults and overrides for runtimes .

How to customize SpringWebFlux WebClient JSON deserialization?

9 Answers9

Linked