This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Boot 3.5.5!

JSON

Spring Boot provides integration with three JSON mapping libraries:

Gson
Jackson 3
JSON-B
Kotlin Serialization

Jackson is the preferred and default library.

Jackson

Auto-configuration for Jackson 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 @JsonComponent annotation that makes it easier to directly register Spring Beans.

You can use the @JsonComponent 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.JsonComponent;

@JsonComponent
public class MyJsonComponent {

	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.JsonComponent

@JsonComponent
class MyJsonComponent {

	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 @JsonComponent beans in the ApplicationContext are automatically registered with Jackson. Because @JsonComponent 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.JsonComponent;
import org.springframework.boot.jackson.ObjectValueDeserializer;
import org.springframework.boot.jackson.ObjectValueSerializer;

@JsonComponent
public class MyJsonComponent {

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

@JsonComponent
class MyJsonComponent {

	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 @JsonMixin and register them with the auto-configured JsonMapper. The registration is performed by Spring Boot’s JsonMixinModule.

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.