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Spring GraphQL - how to map JSON extended scalar to POJO attribute?

I am implementing GraphQL API using Spring for GraphQL project and the GraphQL Java Extended Scalars project for handling JSON attributes since the data attribute I have is dynamic and its structure is not known by the server.
This JSON attribute is part of the payload in a mutation input, which POJO looks like this:
#Accessors(fluent = true)
#Builder
#Data
#JsonDeserialize(builder = MutationInputModel.MutationInputModelBuilder.class)
public class MutationInputModel {
private JsonNode data;
...
}
As exemplified above, I am using Lombok annotations for deserialization and accessors generation.
The data attribute is Jackson's JsonNode type.
However, when calling this mutation I'm getting the following exception:
org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.fasterxml.jackson.databind.JsonNode]: Is it an abstract class?; nested exception is java.lang.InstantiationException
On a previous GraphQL API implementation using this library this same model would work just fine.
My question is how to properly setup JSON scalar type on the POJOs?
I have tried Jackson's ObjectNode and Map<String, Object> with no luck neither.

I ended up implementing my own custom coercing approach so I'll share here for further reference:
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.Collections;
import java.util.Map;
import graphql.schema.Coercing;
import graphql.schema.CoercingParseLiteralException;
import graphql.schema.CoercingParseValueException;
import graphql.schema.CoercingSerializeException;
import static graphql.scalars.ExtendedScalars.Object;
/**
* Custom Coercing implementation in order to parse GQL Objects,
* which get mapped as LinkedHashMap instances by {#link graphql.scalars.object.ObjectScalar}
* into Jackson's JsonNode objects.
*/
public class JsonNodeCoercing implements Coercing<JsonNode, Object> {
private static final Coercing<?, ?> COERCING = Object.getCoercing();
private final ObjectMapper objectMapper;
public JsonNodeCoercing(ObjectMapper objectMapper) {
this.objectMapper = objectMapper;
}
#Override
public Object serialize(Object input) throws CoercingSerializeException {
return input;
}
#Override
public JsonNode parseValue(Object input) throws CoercingParseValueException {
return objectMapper.valueToTree(input);
}
#Override
public JsonNode parseLiteral(Object input) throws CoercingParseLiteralException {
return parseLiteral(input, Collections.emptyMap());
}
#Override
public JsonNode parseLiteral(Object input, Map<String, Object> variables) throws CoercingParseLiteralException {
return objectMapper.valueToTree(COERCING.parseLiteral(input, variables));
}
}
And then this is how the scalar bean config looks like:
#Bean
public RuntimeWiringConfigurer runtimeWiringConfigurer(ObjectMapper objectMapper) {
GraphQLScalarType jsonScalarType = GraphQLScalarType.newScalar()
.name("JSON")
.description("A JSON scalar")
.coercing(new JsonNodeCoercing(objectMapper))
.build();
return wiringBuilder -> wiringBuilder
.scalar(jsonScalarType);
}
If anyone has alternate/simpler approach please share.

Flat JSON in Jackson for class/record/value object with one field

I have a Java record with one field only:
public record AggregateId(UUID id) {}
And a class with the AggregateId field (other fields removed for readability)
public class Aggregate {
public final AggregateId aggregateId;
#JsonCreator
public Aggregate(
#JsonProperty("aggregateId") AggregateId aggregateId
) {
this.aggregateId = aggregateId;
}
}
The implementation above serialize and deserialize JSON with given example:
ObjectMapper objectMapper = new ObjectMapper();
String content = """
{
"aggregateId": {
"id": "3f61aede-83dd-4049-a6ff-337887b6b807"
}
}
""";
Aggregate aggregate = objectMapper.readValue(content, Aggregate.class);
System.out.println(objectMapper.writeValueAsString(aggregate));
How could I change Jackson config to replace JSON by that:
{
"aggregateId": "3f61aede-83dd-4049-a6ff-337887b6b807"
}
without giving up a separate class for AggregateId and access through fields, without getters?
I tried #JsonUnwrapper annotation, but this caused throws
Exception in thread "X" com.fasterxml.jackson.databind.exc.InvalidDefinitionException:
Invalid type definition for type `X`:
Cannot define Creator parameter as `#JsonUnwrapped`: combination not yet supported at [Source: (String)"{
"aggregateId": "3f61aede-83dd-4049-a6ff-337887b6b807"
}"
or
Exception in thread "X" com.fasterxml.jackson.databind.exc.InvalidDefinitionException:
Cannot define Creator property "aggregateId" as `#JsonUnwrapped`:
combination not yet supported at [Source: (String)"{
"aggregateId": "3f61aede-83dd-4049-a6ff-337887b6b807"
}"
Jackson version: 2.13.1
dependencies {
compile "com.fasterxml.jackson.core:jackson-annotations:2.13.1"
compile "com.fasterxml.jackson.core:jackson-databind:2.13.1"
}
Of course, it's possible with a custom serializer/deserializer, but I'm looking for an easier solution because I have many different classes with a similar issue.

The combination of #JsonUnwrapped and #JsonCreator is not supported yet, so we can generate a solution like this:
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonUnwrapped;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import java.util.UUID;
public class AggregateTest {
static record AggregateId(#JsonProperty("aggregateId") UUID id) {}
static class Aggregate {
#JsonUnwrapped
#JsonProperty(access = JsonProperty.Access.READ_ONLY)
public final AggregateId _aggregateId;
public final String otherField;
#JsonCreator
public Aggregate(#JsonProperty("aggregateId") UUID aggregateId,
#JsonProperty("otherField") String otherField) {
this._aggregateId = new AggregateId(aggregateId);
this.otherField = otherField;
}
}
public static void main(String[] args) throws JsonProcessingException {
String rawJson =
"{\"aggregateId\": \"1f61aede-83dd-4049-a6ff-337887b6b807\"," +
"\"otherField\": \"İsmail Y.\"}";
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
Aggregate aggregate = objectMapper
.readValue(rawJson, Aggregate.class);
System.out.println(objectMapper
.writeValueAsString(aggregate));
}
}
Here we briefly get rid of the #JsonUnwrapped field.
We get the UUID with the name aggregateId and create an AggregateId record.
Detailed explanations about it:
https://github.com/FasterXML/jackson-databind/issues/1467
https://github.com/FasterXML/jackson-databind/issues/1497

How to convert a JsonNode instance to an actual pojo

At a certain point in my code, I have parse a JSON document, represented as a string, to a JsonNode, because I don't know yet the actual target pojo class type.
Now, some time later, I know the Class instance of the pojo and I want to convert this JsonNode to an actual pojo of that class (which is annotated with the proper #JsonProperty annotations). Can this be done? If so, how?
I am working with Jackson 2.10.x.

In this case you can use two methods:
treeToValue
convertValue
See below example:
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;
import java.util.StringJoiner;
public class JsonNodeConvertApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
ObjectMapper mapper = new ObjectMapper();
JsonNode node = mapper.readTree(jsonFile);
System.out.println(mapper.treeToValue(node, Message.class));
System.out.println(mapper.convertValue(node, Message.class));
}
}
class Message {
private int id;
private String body;
// getters, setters, toString
}
Above code for JSON payload like below:
{
"id": 1,
"body": "message body"
}
prints:
Message[id=1, body='message body']
Message[id=1, body='message body']

How to not create many classes just for serialising nested JSON payload?

I've JSON message coming in from rabbitmq and has the following format:
{
messageId: 123,
content: {
id: "P123456",
status: false,
error: {
description: "Something has gone wrong",
id: 'E400'
}
}
}
As you can see, the message has a few nested objects within them.
When this message comes in, I will serialise it using Jackson. Right now, however, I have to create multiple classes just for one single message.
In the example message above, I have to create 3 classes just for serialising and transforming it into a class MainMessage, like so:
public class MainMessage {
private int messageId;
private MessageContentObject content;
// getters/setters...
}
public class MessageContentObject {
private String id;
private boolean status;
private MessageErrorObject error;
// getters/setters...
}
public class MessageErrorObject {
private String description;
private string id;
// getters/setters...
}
This feels very cumbersome because in some of the messages, the nesting can be pretty deep and I will have to create a lot of classes just for the purpose of having the JSON payload transformed into the MainMessage class object. The MessageContentObject and MessageErrorObject are mostly redundant because I will never use the classes directly anywhere else in the code. I would still the values in them through MainMessage though, for example:
#RabbitListener
public void consumeMessage(MainMessage msg) {
System.out.println(msg.getContent().getError().getDescription());
}
I'm using Spring with Spring Boot.
Is this really the only way I can do when it comes to dealing with nested JSON payloads?

First, when the message comes in you Deserialize it.
Now, if you don't want to create the whole data structure to look like your incoming JSON, you can go for a Map like this
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonCreator;
import java.util.Collections;
import java.util.Map;
public class Message {
private final Map<String, Object> details;
#JsonCreator // Deserialize the JSON using this creator
public Message(final Map<String, Object> details) {
super();
this.details = details;
}
#JsonAnyGetter // Serialize this class using the data from the map
public Map<String, Object> getDetails() {
return Collections.unmodifiableMap(details);
}
}
In this way, you won't need to change your Message class every time your incoming JSON changes.
However, this approach is useful only when you'll not be manipulating the data too much.

if you don't want to create the whole data structure or you only need a small portion of the response recieved at a time you can use Jackson JsonNode
import com.fasterxml.jackson.databind.JsonNode;
public class Message {
private JsonNode messageDetails;
/**
* Constructor used to transform your object into jsonNode.
*
* #param messageDetailsResponse
*/
public Message(Object messageDetailsResponse) {
this.messageDetails = JsonUtils.getNode(messageDetailsResponse);
}
//Simply create getters for accessing the data you want when you want it
public String getId() {
return messageDetails.findValue("messageId").asText();
}
//You can also use it later to map a portion of response to an model class
public Content getContent(){
return JsonUtils.fromJsonNode(messageDetails.get("content"),Content.class)
}
}
The Code for JsonUtils
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.slf4j.Slf4j;
#Slf4j
final public class JsonUtils {
/**
* The Object Mapper constant to deal with JSON to/from conversion activities.
*/
private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
public static JsonNode getNode(Object anyObject) {
try {
return OBJECT_MAPPER.readTree(OBJECT_MAPPER.writeValueAsBytes(anyObject));
} catch (IOException e) {
log.error(e.getMessage(), e);
}
}
public static <T> T fromJsonNode(final JsonNode node, final Class<T> clazz)
throws JsonProcessingException {
return OBJECT_MAPPER.treeToValue(node, clazz);
}

Some suggestions:
Consider using Lombok to reduce the code you need to write (getters setters etc.) - will make creating classes less of a problem.
Consider using static inner classes - will mean you need less files.
If you still prefer to not write your classes down, you can deserealise to a String and traverse it using Gson or similar libraries.

ObjectMapper not considering annotations

I have the below piece of code which would convert an annotated Java object into Json String.
try {
String jsonString = mapper.writeValueAsString(obj);
LOGGER.debug("logAsJson", jsonString);
} catch (Exception e) {
LOGGER.warn("logAsJson", "Exception in logging only. Nothing critical! ", e);
}
And my class would look something like this
public class Car {
#JsonProperty("capabilities")
private List<Capability> capability = new ArrayList<Capability>();
#JsonProperty("periodicity")
#NotNull
private Periodicity periodicity;
#JsonProperty("car_driver")
private List<carDriver> carDriver = new ArrayList<carDriver>();
}
Problem is that while creating the json string from the object, object mapper is not considering the annotations for field names.
Thanks in advance.

You might have imported the json annotation and the object mapper from different library versions. Make sure they are from the same library.
Example,
import com.fasterxml.jackson.annotation.JsonProperty;
and
import com.fasterxml.jackson.databind.ObjectMapper;