How do I parse snake case fields in a FeignClient response json? - spring-boot

Question

I have configured a FeignClient in my spring boot webapp where I'm calling an external api that returns the following object.
public class Issue {
private Assignee assignee;
private Date createdAt;
private Date updatedAt;
private Date closedAt;
private String description;
private Date dueDate;
public Assignee getAssignee() {
return assignee;
}
public void setAssignee(Assignee assignee) {
this.assignee = assignee;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public Date getDueDate() {
return dueDate;
}
public void setDueDate(Date dueDate) {
this.dueDate = dueDate;
}
public Date getUpdatedAt() {
return updatedAt;
}
public void setUpdatedAt(Date updatedAt) {
this.updatedAt = updatedAt;
}
public Date getClosedAt() {
return closedAt;
}
public void setClosedAt(Date closedAt) {
this.closedAt = closedAt;
}
#Override
public String toString() {
return (JacksonJson.toJsonString(this));
}
}
The fields updatedAt, createdAt and closedAt are all in snake case. All multi-word fields show up as null. Is there any way of configuring the FeignClient's Jackson parser so that it can process snake case characters? Note, that I cannot change the default Jackson Parser for my spring boot webapp because I myself render json in camel case. I just need to configure this parser on the FeignClient that I'm using to connect to an external REST api.
I have verified that the json response returned from the api call contains valid values in each of these json fields.

Answer 1

Here's how I solved it. I created a custom JacksonParser as a Spring Bean.
#Configuration(proxyBeanMethods = false)
public class FeignClientDateFormatConfig {
#Bean
public Decoder feignDecoder() {
HttpMessageConverter jacksonConverter = new MappingJackson2HttpMessageConverter(customObjectMapper());
ObjectFactory<HttpMessageConverters> objectFactory = () -> new HttpMessageConverters(jacksonConverter);
return new ResponseEntityDecoder(new SpringDecoder(objectFactory));
}
public ObjectMapper customObjectMapper() {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
return objectMapper;
}
}
This successfully parses all snake case properties.
Please note that this has a severe limitation. If you have multiple FeignClients and only one of them returns snake-case json, then you're out of luck. This overrides the default FeignClient config. The only workaround possible with this solution is to move your FeignClient calls into a separate microservice so other FeignClient calls are not affected.