java jackson 自定義_Spring Cloud Feign Jackson自定義配置

Spring Cloud Feign 預設支援Spring MVC的注解 使用相同的HttpMessageConverters類轉換

官方文檔說明：

Spring Cloud adds support for Spring MVC annotations and for using the same HttpMessageConverters used by default in Spring Web.

但是我們一般在傳回給前端JSON格式的時候 都會把相應的 NULL值轉為相應的””，這使得Spring Cloud Feign也使用相同的Jackson配置，例如我們項目的配置

@Bean

public ObjectMapper jacksonObjectMapper() {

ObjectMapper objectMapper = new ObjectMapper();

// objectMapper.setSerializationInclusion(Include.NON_NULL);

objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer() {

@Override

public void serialize(Object value, JsonGenerator jg, SerializerProvider sp)

throws IOException, JsonProcessingException {

jg.writeString("");

sp.getDefaultNullKeySerializer();

}

});

objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);

return objectMapper;

}

出現的問題：

在服務通過Feign進行請求的時候，傳NULL值引用類型值時，會出現類型轉換異常，由于HttpMessageConverters直接把NULL轉為了””。

解決思路：

自定義配置 Spring Cloud Feign  Encoder與Decoder

官方文檔說明：

Spring Cloud Netflix provides the following beans by default for feign (BeanType beanName: ClassName):

Decoder feignDecoder: ResponseEntityDecoder (which wraps a SpringDecoder)

Encoder feignEncoder: SpringEncoder

Logger feignLogger: Slf4jLogger

Contract feignContract: SpringMvcContract

Feign.Builder feignBuilder: HystrixFeign.Builder

Client feignClient: if Ribbon is enabled it is a LoadBalancerFeignClient, otherwise the default feign client is used.

解決方法：

統一配置Feign 的Encoder和Decoder的Jackson轉換方式

@Configuration

public class CustomFeignConfig {

@Bean

public Decoder feignDecoder() {

HttpMessageConverter jacksonConverter = new MappingJackson2HttpMessageConverter(customObjectMapper());

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

return new ResponseEntityDecoder(new SpringDecoder(objectFactory));

}

@Bean

public Encoder feignEncoder(){

HttpMessageConverter jacksonConverter = new MappingJackson2HttpMessageConverter(customObjectMapper());

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

return new SpringEncoder(objectFactory);

}

public ObjectMapper customObjectMapper(){

ObjectMapper objectMapper = new ObjectMapper();

//Customize as much as you want

objectMapper.configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);

return objectMapper;

}

}