Spring Boot - RestController Deserializing YAML Uploads?

How can I configure a Spring Boot RestController to accept YAML uploads?

The following results in a 415. I can see from debugging that the MappingJackson2HttpMessageConverter instances in my Spring context only support [application/json;charset=UTF-8, application/*+json;charset=UTF-8]. I can't be the only Spring Boot user trying to do this, and I'm surprised it doesn't just work - most things do in Spring Boot!

I've got the YAML dataformat in my POM:

    <dependency>
        <groupId>com.fasterxml.jackson.dataformat</groupId>
        <artifactId>jackson-dataformat-yaml</artifactId>
    </dependency>

My RestController has a method thus:

@RequestMapping(method=RequestMethod.POST, value="/", consumes="application/yaml")
public String upload(@RequestBody Declaration declaration) {
    //Do stuff
}

And my test:

@Test
public void triggersConvergence() throws Exception {
    ClassPathResource fixture = new ClassPathResource("declaration.yml");
    HttpHeaders requestHeaders = new HttpHeaders();
    requestHeaders.add("Content-Type", "application/yaml");
    requestHeaders.add("Accept", "application/json");

    URI uri = new URI("http://127.0.0.1:"+port);
    byte[] bytes = new byte[(int)fixture.contentLength()];
    fixture.getInputStream().read(bytes);
    RequestEntity<byte[]> postRequest = new RequestEntity<byte[]>(bytes, requestHeaders, HttpMethod.POST, uri);

    ResponseEntity<String> response = rest.exchange(postRequest, String.class);
    assertThat(response.getStatusCode(), is(HttpStatus.OK));
    assertThat(response.getBody(), is("Converged org my-lovely-org"));
}

While this functionality is not available in Spring it's easy to add using YAMLMapper it in 2 simple steps:

1. Define your own HttpMessageConverter that supports Content-Type: application/yaml:

    final class YamlJackson2HttpMessageConverter extends AbstractJackson2HttpMessageConverter {
        YamlJackson2HttpMessageConverter() {
            super(new YAMLMapper(),
                    MediaType.parseMediaType("application/yaml"),
                    MediaType.parseMediaType("application/*+yaml"));
        }
    }
   

2. Register your converter:

    @Configuration
    public class YamlConfiguration extends WebMvcConfigurerAdapter {
        @Override
        public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
            converters.add(new YamlJackson2HttpMessageConverter());
        }
    }
   

Enjoy controller methods consuming and producing application/yaml from POJOs.