I retrieve a JSON string from internet; like most JSON I've seen it includes long keys that are separated by underscores. Essentially, my goal is to deserialize JSON into java-objects, but I don't use underscores in java-code.
For instance, I might have a User
class with firstName
field in camel-case, simultaneously I need somehow to tell Jackson to map first_name
key from JSON to firstName
class field. Is it possible?
class User{
protected String firstName;
protected String getFirstName(){return firstName;}
}
The above answers regarding @JsonProperty
and CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES
are 100% accurate, although some people (like me) might be trying to do this inside a Spring MVC application with code-based configuration. Here's sample code (that I have inside Beans.java
) to achieve the desired effect:
@Bean
public ObjectMapper jacksonObjectMapper() {
return new ObjectMapper().setPropertyNamingStrategy(
PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
}
If you want this for a Single Class, you can use the PropertyNamingStrategy with the @JsonNaming, something like this:
@JsonNaming(PropertyNamingStrategy.LowerCaseWithUnderscoresStrategy.class)
public static class Request {
String businessName;
String businessLegalName;
}
Will serialize to:
{
"business_name" : "",
"business_legal_name" : ""
}
Since Jackson 2.7
the LowerCaseWithUnderscoresStrategy
in deprecated in favor of SnakeCaseStrategy
, so you should use:
@JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
public static class Request {
String businessName;
String businessLegalName;
}
If its a spring boot application, In application.properties file, just use
spring.jackson.property-naming-strategy=SNAKE_CASE
Or Annotate the model class with this annotation.
@JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
Annotating all model classes looks to me as an overkill and Kenny's answer didn't work for me https://stackoverflow.com/a/43271115/4437153. The result of serialization was still camel case.
I realised that there is a problem with my spring configuration, so I had to tackle that problem from another side. Hopefully someone finds it useful, but if I'm doing something against springs' rules then please let me know.
Solution for Spring MVC 5.2.5 and Jackson 2.11.2
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
converter.setObjectMapper(objectMapper);
converters.add(converter);
}
}
The current best practice is to configure Jackson within the application.yml
(or properties
) file.
Example:
spring:
jackson:
property-naming-strategy: SNAKE_CASE
If you have more complex configuration requirements, you can also configure Jackson programmatically.
import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
@Configuration
public class JacksonConfiguration {
@Bean
public Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder() {
return new Jackson2ObjectMapperBuilder()
.propertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
// insert other configurations
}
}
You can configure the ObjectMapper
to convert camel case to names with an underscore:
objectMapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
Or annotate a specific model class with this annotation:
@JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
Before Jackson 2.7, the constant was named:
PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES
There are few answers here indicating both strategies for 2 different versions of Jackson library below:
For Jackson 2.6.*
ObjectMapper objMapper = new ObjectMapper(new JsonFactory()); // or YAMLFactory()
objMapper.setNamingStrategy(
PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
For Jackson 2.7.*
ObjectMapper objMapper = new ObjectMapper(new JsonFactory()); // or YAMLFactory()
objMapper.setNamingStrategy(
PropertyNamingStrategy.SNAKE_CASE);
Source: Stackoverflow.com