How to set custom Jackson ObjectMapper with Spring Cloud Netflix Feign

Question

I'm running into a scenario where I need to define a one-off @FeignClient for a third party API. In this client I'd like to use a custom Jackson ObjectMapper that differs from my @Primary one. I know it is possible to override spring's feign configuration defaults however it is not clear to me how to simply override the ObjectMapper just by this specific client.

Answer 1

Per the documentation, you can provide a custom decoder for your Feign client as shown below.

Feign Client Interface:

@FeignClient(value = "foo", configuration = FooClientConfig.class)
public interface FooClient{
    //Your mappings
}

Feign Client Custom Configuration:

@Configuration
public class FooClientConfig {

    @Bean
    public Decoder feignDecoder() {
        HttpMessageConverter jacksonConverter = new MappingJackson2HttpMessageConverter(customObjectMapper());

        HttpMessageConverters httpMessageConverters = new HttpMessageConverters(jacksonConverter);
        ObjectFactory<HttpMessageConverters> objectFactory = () -> httpMessageConverters;


        return new ResponseEntityDecoder(new SpringDecoder(objectFactory));
    }

    public ObjectMapper customObjectMapper(){
        ObjectMapper objectMapper = new ObjectMapper();
        //Customize as much as you want
        return objectMapper;
    }
}

Answer 2

follow @NewBie`s answer, i can give the better one...

  @Bean
  public Decoder feignDecoder() {
    return new JacksonDecoder();
  }

if you want use jackson message converter in feign client, please use JacksonDecoder, because SpringDecoder will increase average latency of feignclient call in production.

    <!-- feign-jackson decoder -->
    <dependency>
      <groupId>io.github.openfeign</groupId>
      <artifactId>feign-jackson</artifactId>
      <version>10.1.0</version>
    </dependency>

Answer 3

@NewBie's answer has serious performance problems. During the new HttpMessageConverters process, loadclass will be performed, resulting in a large number of thread block. If you have used this code, please modify it as follows:

ObjectFactory<HttpMessageConverters> objectFactory = () -> new HttpMessageConverters(jacksonConverter);

change to

HttpMessageConverters httpMessageConverters = new HttpMessageConverters(jacksonConverter);
ObjectFactory<HttpMessageConverters> objectFactory = () -> httpMessageConverters;

You can use JMeter and Arthas to reproduce this phenomenon, and the modified program has been greatly improved.

Answer 4

Define a custom decoder as below, annotated with @Configuration and set as parameter for the feign client interface, configuration = CustomFeignClientConfig.class

@Configuration
public class CustomFeignClientConfig {
    @Bean
    public Decoder feignDecoder() {
        return (response, type) -> {
            String bodyStr = Util.toString(response.body().asReader(Util.UTF_8));
            JavaType javaType = TypeFactory.defaultInstance().constructType(type);
            return new ObjectMapper().readValue( bodyStr, javaType);
        };
    }
}

Answer 5

you can use SpringDecoder and SpringEncoder.

public SpringDecoder(ObjectFactory<HttpMessageConverters> messageConverters)

is deprecated. you should use another constructor:

public SpringDecoder(ObjectFactory<HttpMessageConverters> messageConverters,
            ObjectProvider<HttpMessageConverterCustomizer> customizers)

for example:

    @Bean
    public Decoder feignDecoder(ObjectProvider<HttpMessageConverterCustomizer> customizers) {
//        HttpMessageConverter<?> jacksonConverter = new MappingJackson2HttpMessageConverter(customObjectMapper());
//        HttpMessageConverters httpMessageConverters = new HttpMessageConverters(jacksonConverter);
        
        var httpMessageConverters = new HttpMessageConverters();
        return new ResponseEntityDecoder(new SpringDecoder(() -> httpMessageConverters, customizers));
    }

    @Bean
    public Encoder feignEncoder() {
        var httpMessageConverters = new HttpMessageConverters();
        return new SpringEncoder(() -> httpMessageConverters);
    }

if you want to write a decode time customizer, then you can wright like this:

@Component
public class HttpMessageCustomizer implements HttpMessageConverterCustomizer {
    @Override
    public void accept(List<HttpMessageConverter<?>> httpMessageConverters) {
        //customizing
    }

    @Override
    public Consumer<List<HttpMessageConverter<?>>> andThen(Consumer<? super List<HttpMessageConverter<?>>> after) {
        return HttpMessageConverterCustomizer.super.andThen(after);
    }
}