Jackson JSON Serialization in Spring Boot

Direct Answer

Spring MVC reads and writes HTTP bodies through an HttpMessageConverter. When a Jackson converter is selected, the configured Jackson mapper deserializes JSON into an @RequestBody DTO and serializes a value returned by a @RestController into JSON. DTO design, mapper settings, validation, and error handling complete the contract.

Deep Dive & Architecture

Handler mapping first selects a controller method from its path, HTTP method, and media conditions. Argument resolution sees @RequestBody and delegates to a converter that can read the request's Content-Type into the declared target type. The Jackson converter parses tokens, constructs the object, converts property values, and applies the configured mapping rules.

The reverse path begins with the controller's return value. Spring chooses a converter for the negotiated response media type, and Jackson serializes the response DTO. Request and response DTOs define a deliberate public shape. Global naming or time conventions can be configured centrally, while one-off contract names can use focused annotations or a custom serializer when normal mapping is not enough.

Malformed JSON fails during message conversion before controller logic receives a DTO. Valid JSON can still violate Bean Validation or domain rules afterward. Serialization can also fail, for example when a custom serializer throws. These stages should map to safe, consistent error responses rather than expose parser or mapping internals.

Deserialization is a trust boundary. Unknown-member handling, polymorphic input, numeric coercion, null behavior, and accepted date formats should be intentional. Mapper types and defaults can differ between Spring Boot and Jackson generations, so a compatibility-sensitive API should configure and test the actual mapper used by that application instead of relying on a remembered default.

Code Example

import com.fasterxml.jackson.annotation.JsonProperty;
import org.springframework.web.bind.annotation.*;

record CreateUserRequest(
        @JsonProperty("display_name") String displayName,
        String email) {}

record UserResponse(long id, String displayName) {}

@RestController
@RequestMapping("/users")
final class UserController {
    @PostMapping
    UserResponse create(@RequestBody CreateUserRequest request) {
        return new UserResponse(42, request.displayName());
    }
}

With Jackson and Spring MVC configured, the request member display_name maps to the Java component displayName, and the returned record is serialized as a JSON response.