json - Spring boot Jersey Jackson

Question

I have a question related to the Jackson configuration on my Spring boot project

As described on spring boot blog

I try to customize my Object serialization.

After added a new config bean in my config

@Bean
public Jackson2ObjectMapperBuilder jacksonBuilder() {
    Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();

    builder.propertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
    return builder;
}

When I try to output an instance of my class User the json result is not in CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES

Class User {
    private String firstName = "Joe Blow";

    public String getFirstName() {
        return firstName;
    }
}

json output is :

{
  "firstName": "Joe Blow"
}

and not

{
  "first_name": "Joe Blow"
}

Maybe I need to register something in my Jersey config to activate my custom obejctMapper Config

@Configuration
public class JerseyConfig extends ResourceConfig {
    public JerseyConfig() {
        packages("my.package);
    }
}

Thanks

Answer 1

The general way to configure the ObjectMapper for JAX-RS/Jersey applications is use a ContextResolver. For example

@Provider
public class ObjectMapperContextResolver implements ContextResolver<ObjectMapper> {

    private final ObjectMapper mapper;

    public ObjectMapperContextResolver() {
        mapper = new ObjectMapper();
        mapper.setPropertyNamingStrategy(
            PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES
        );
    }

    @Override
    public ObjectMapper getContext(Class<?> type) {
        return mapper;
    }
}

It should be picked up with the package scan, or you can explicitly register it, if it's not within the package scope

public JerseyConfig() {
    register(new ObjectMapperContextResolver());
    // Or if there's is an injection required
    // register it as a .class instead of instance
}

The ContextResolver is called during the marshalling and unmarshalling. The class/type being serialzed or deserialized into will be passed to the getContext method. So you could even use more than one mapper for different types, or even more use cases.

---

UPDATE

Starting from Spring Boot 1.4, you can just create an ObjectMapper Spring bean, and Spring Boot will create the ContextResolver for you, and use your ObjectMapper

// in your `@Configuration` file.
@Bean
public ObjectMapper mapper() {}