This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Boot 3.5.6!

JSON

Spring Boot provides integration with the following JSON mapping libraries:

Jackson 3
Jackson 2
Gson
JSON-B
Kotlin Serialization

Jackson 3 is the preferred and default library.

Support for Jackson 2 is deprecated and will be removed in a future Spring Boot 4.x release. It is provided purely to ease the migration from Jackson 2 to Jackson 3 and should not be relied up in the longer term.

Jackson 3

Auto-configuration for Jackson 3 is provided and Jackson is part of spring-boot-starter-json. When Jackson is on the classpath a JsonMapper bean is automatically configured. Several configuration properties are provided for customizing the configuration of the JsonMapper.

Custom Serializers and Deserializers

If you use Jackson to serialize and deserialize JSON data, you might want to write your own ValueSerializer and ValueDeserializer classes. Custom serializers are usually registered with Jackson through a module, but Spring Boot provides an alternative @JacksonComponent annotation that makes it easier to directly register Spring Beans.

You can use the @JacksonComponent annotation directly on ValueSerializer, ValueDeserializer or KeyDeserializer implementations. You can also use it on classes that contain serializers/deserializers as inner classes, as shown in the following example:

Java
Kotlin

import tools.jackson.core.JsonGenerator;
import tools.jackson.core.JsonParser;
import tools.jackson.databind.DeserializationContext;
import tools.jackson.databind.JsonNode;
import tools.jackson.databind.SerializationContext;
import tools.jackson.databind.ValueDeserializer;
import tools.jackson.databind.ValueSerializer;

import org.springframework.boot.jackson.JacksonComponent;

@JacksonComponent
public class MyJacksonComponent {

	public static class Serializer extends ValueSerializer<MyObject> {

		@Override
		public void serialize(MyObject value, JsonGenerator jgen, SerializationContext context) {
			jgen.writeStartObject();
			jgen.writeStringProperty("name", value.getName());
			jgen.writeNumberProperty("age", value.getAge());
			jgen.writeEndObject();
		}

	}

	public static class Deserializer extends ValueDeserializer<MyObject> {

		@Override
		public MyObject deserialize(JsonParser jsonParser, DeserializationContext ctxt) {
			JsonNode tree = jsonParser.readValueAsTree();
			String name = tree.get("name").stringValue();
			int age = tree.get("age").intValue();
			return new MyObject(name, age);
		}

	}

}

import tools.jackson.core.JsonGenerator
import tools.jackson.core.JsonParser
import tools.jackson.databind.DeserializationContext
import tools.jackson.databind.JsonNode
import tools.jackson.databind.SerializationContext
import tools.jackson.databind.ValueDeserializer
import tools.jackson.databind.ValueSerializer

import org.springframework.boot.jackson.JacksonComponent

@JacksonComponent
class MyJacksonComponent {

	class Serializer : ValueSerializer<MyObject>() {
		override fun serialize(value: MyObject, jgen: JsonGenerator, serializers: SerializationContext) {
			jgen.writeStartObject()
			jgen.writeStringProperty("name", value.name)
			jgen.writeNumberProperty("age", value.age)
			jgen.writeEndObject()
		}
	}

	class Deserializer : ValueDeserializer<MyObject>() {
		override fun deserialize(jsonParser: JsonParser, ctxt: DeserializationContext): MyObject {
			val tree = jsonParser.readValueAsTree<JsonNode>()
			val name = tree["name"].stringValue()
			val age = tree["age"].intValue()
			return MyObject(name, age)
		}
	}

}

All @JacksonComponent beans in the ApplicationContext are automatically registered with Jackson. Because @JacksonComponent is meta-annotated with @Component, the usual component-scanning rules apply.

Spring Boot also provides ObjectValueSerializer and ObjectValueDeserializer base classes that provide useful alternatives to the standard Jackson versions when serializing objects. See ObjectValueSerializer and ObjectValueDeserializer in the API documentation for details.

The example above can be rewritten to use ObjectValueSerializer and ObjectValueDeserializer as follows:

Java
Kotlin

import tools.jackson.core.JsonGenerator;
import tools.jackson.core.JsonParser;
import tools.jackson.databind.DeserializationContext;
import tools.jackson.databind.JsonNode;
import tools.jackson.databind.SerializationContext;

import org.springframework.boot.jackson.JacksonComponent;
import org.springframework.boot.jackson.ObjectValueDeserializer;
import org.springframework.boot.jackson.ObjectValueSerializer;

@JacksonComponent
public class MyJacksonComponent {

	public static class Serializer extends ObjectValueSerializer<MyObject> {

		@Override
		protected void serializeObject(MyObject value, JsonGenerator jgen, SerializationContext context) {
			jgen.writeStringProperty("name", value.getName());
			jgen.writeNumberProperty("age", value.getAge());
		}

	}

	public static class Deserializer extends ObjectValueDeserializer<MyObject> {

		@Override
		protected MyObject deserializeObject(JsonParser jsonParser, DeserializationContext context, JsonNode tree) {
			String name = nullSafeValue(tree.get("name"), String.class);
			int age = nullSafeValue(tree.get("age"), Integer.class);
			return new MyObject(name, age);
		}

	}

}

import tools.jackson.core.JsonGenerator
import tools.jackson.core.JsonParser
import tools.jackson.databind.DeserializationContext
import tools.jackson.databind.JsonNode
import tools.jackson.databind.SerializationContext

import org.springframework.boot.jackson.JacksonComponent;
import org.springframework.boot.jackson.ObjectValueDeserializer
import org.springframework.boot.jackson.ObjectValueSerializer

@JacksonComponent
class MyJacksonComponent {

	class Serializer : ObjectValueSerializer<MyObject>() {
		override fun serializeObject(value: MyObject, jgen: JsonGenerator, context: SerializationContext) {
			jgen.writeStringProperty("name", value.name)
			jgen.writeNumberProperty("age", value.age)
		}
	}

	class Deserializer : ObjectValueDeserializer<MyObject>() {
		override fun deserializeObject(jsonParser: JsonParser, context: DeserializationContext,
				tree: JsonNode): MyObject {
			val name = nullSafeValue(tree["name"], String::class.java) ?: throw IllegalStateException("name is null")
			val age = nullSafeValue(tree["age"], Int::class.java) ?: throw IllegalStateException("age is null")
			return MyObject(name, age)
		}
	}

}

Mixins

Jackson has support for mixins that can be used to mix additional annotations into those already declared on a target class. Spring Boot’s Jackson auto-configuration will scan your application’s packages for classes annotated with @JacksonMixin and register them with the auto-configured JsonMapper. The registration is performed by Spring Boot’s JacksonMixinModule.

Jackson 2

Deprecated auto-configuration for Jackson 2 is provided by the spring-boot-jackson2 module. When this module is on the classpath a ObjectMapper bean is automatically configured. Several spring.jackson2.* configuration properties are provided for customizing the configuration. To take more control, define one or more Jackson2ObjectMapperBuilderCustomizer beans.

When both Jackson 3 and Jackson 2 are present, various configuration properties can be used to indicate that Jackson 2 is preferred:

spring.graphql.rsocket.preferred-json-mapper
spring.http.codecs.preferred-json-mapper (used by Spring WebFlux and reactive HTTP clients)
spring.http.converters.preferred-json-mapper (used by Spring MVC and imperative HTTP clients)
spring.rsocket.preferred-mapper
spring.websocket.messaging.preferred-json-mapper

In each case, set the relevant property to jackson2 to indicate that Jackson 2 is preferred.

Gson

Auto-configuration for Gson is provided. When Gson is on the classpath a Gson bean is automatically configured. Several spring.gson.* configuration properties are provided for customizing the configuration. To take more control, one or more GsonBuilderCustomizer beans can be used.

JSON-B

Auto-configuration for JSON-B is provided. When the JSON-B API and an implementation are on the classpath a Jsonb bean will be automatically configured. The preferred JSON-B implementation is Eclipse Yasson for which dependency management is provided.

Kotlin Serialization

Auto-configuration for Kotlin Serialization is provided. When kotlinx-serialization-json is on the classpath a Json bean is automatically configured. Several spring.kotlin.serialization.* configuration properties are provided for customizing the configuration.