Spring WebClient call to Rest-Service: Exception from Jaxb2XmlDecoder

Question

I'm currentlty struggling with Springs reactive WebClient calling a Rest-Service. I get an UnsupportedOperationException of the decodeToMono-function from Springs Jaxb2XmlDecoder.

public Mono<T> decodeToMono(Publisher<DataBuffer> inputStream, ResolvableType elementType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
  throw new UnsupportedOperationException();
}

My WebClient call:

ResponseEntity<MyAsyncResponse> result = webClient.post()
        .contentType(MediaType.APPLICATION_XML)
        .syncBody(payload)
        .exchange()
        .flatMap(res -> res.toEntity(MyAsyncResponse.class))
        .block();

The Rest-Service:

@RestController
public class MyAsyncController {

  @PostMapping(path = "foo")
  private CompletableFuture<MyAsyncResponse> getFoo() {
    return getMyAsyncResponse();
  }

  ...

What do I have to configure, that a suitable Decoder-implementation is used? It's a plain old Spring-MVC (v5.0.3) application, not Spring-Boot.

Answer 1

Jaxb2XmlDecoder did not implement decodeToMono, but it is now fixed via SPR-16759. So just upgrading to Spring Framework 5.0.6+ / Spring Boot 2.0.2+ should avoid the reported exception.

Answer 2

This is known issue of the Jaxb2XmlDecoder in Spring 5.0.3, which is unable to decode simple single message (however, it can decode message streaming).

See base class - https://github.com/spring-projects/spring-framework/blob/master/spring-core/src/main/java/org/springframework/core/codec/AbstractDecoder.java

Jaxb2XmlDecoder does not override "decodeToMono" method.

To fix this create your own decoder and update configuration by the following style:

On Kotlin:

@Bean
open fun webFluxConfigurer(myReader: MyReader,                               
                           myWriter: MyWriter): WebFluxConfigurer {
    return object : WebFluxConfigurer {
        override fun configureHttpMessageCodecs(configurer: ServerCodecConfigurer) {
            // disable default codecs, because of problematic XML serialization in Jaxb2XmlDecoder
            configurer.registerDefaults(false)

            configurer.customCodecs().decoder(myReader)

            configurer.customCodecs().encoder(myWriter)
        }
    }

}

Or on Java:

@Bean
WebFluxConfigurer webFluxConfigurer(MyReader myReader, MyWriter myWriter){ 
    return new WebFluxConfigurer() {
        @Override
        public void configureHttpMessageCodecs(ServerCodecConfigurer configurer) {
            // disable default codecs, because of problematic XML serialization in Jaxb2XmlDecoder
            configurer.registerDefaults(false);

            configurer.customCodecs().decoder(myReader);

            configurer.customCodecs().encoder(myWriter);
        }
    };

}