How to Configure Jackson to Map Underscore JSON Keys to Camel Case Java Fields?

How can I configure Jackson to deserialize JSON keys using underscores to camel case property names in Java objects?

class User {
    protected String firstName;
    protected String getFirstName() { return firstName; }
}

Jackson, a popular JSON processing library in Java, provides ways to customize the mapping of JSON keys to Java object fields. By default, Jackson expects property names to be in camel case. If your JSON keys use underscores (e.g., `first_name`), you can easily configure Jackson to handle this mapping automatically.

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.PropertyNamingStrategies;

public class JacksonExample {
    public static void main(String[] args) throws Exception {
        String json = "{\"first_name\":\"John\"}";
        ObjectMapper mapper = new ObjectMapper();
        mapper.setPropertyNamingStrategy(PropertyNamingStrategies.SNAKE_CASE);
        User user = mapper.readValue(json, User.class);
        System.out.println(user.getFirstName()); // Outputs: John
    }
}

Causes

• Many APIs return JSON data with keys formatted in snake_case (using underscores).
• Java naming conventions typically use camelCase for variable names.

Solutions

• Use the `PropertyNamingStrategies` class in Jackson to change how it maps names.
• In your `ObjectMapper` configuration, set the naming strategy to `PropertyNamingStrategies.SnakeCaseStrategy` to automatically convert underscore keys to camel case.
• Ensure your Java class fields are defined in camel case and provide corresponding getters and setters.

Mistake: Forgetting to set the property naming strategy on the ObjectMapper.

Solution: Always configure your ObjectMapper with the desired naming strategy before processing JSON.

Mistake: Using fields without proper getters or setters may lead to deserialization issues.

Solution: Ensure that the class has properly defined getters and setters for the fields being deserialized.