Cannot deserialize from Object value (no delegate- or property-based Creator) using Jackson

Scripta14 :

I'm trying to deserialise below JSON payload with Jackson:

{"code":null,"reason":"subscription yet available","message":"{ Message:\"subscription yet available\", SubscriptionUID:\"46b62920-c519-4555-8973-3b28a7a29463\" }"}

but I'm getting this JsonMappingException:

Cannot construct instance of `com.ids.utilities.DeserializeSubscription` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (String)"{"code":null,"reason":"subscription yet available","message":"{ Message:\"subscription yet available\", SubscriptionUID:\"46b62920-c519-4555-8973-3b28a7a29463\" }"}"; line: 1, column: 2]

I've created two classes. The first class:

import lombok.Data;

@Data
public class DeserializeSubscription {

    private String code;
    private String reason;
    private MessageSubscription message;


    public DeserializeSubscription(String code, String reason, MessageSubscription message) {
        super();
        this.code = code;
        this.reason = reason;
        this.message = message;
    }

and the second class

import lombok.Data;

@Data
public class MessageSubscription {

    private String message;
    private String subscriptionUID;


    public MessageSubscription(String message, String subscriptionUID) {
        super();
        this.message = message;
        this.subscriptionUID = subscriptionUID;
    }

In the main class:

                 try 
                 {

                    ObjectMapper mapper = new ObjectMapper();
                    mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
                    DeserializeSubscription desSub=null;

                    desSub=mapper.readValue(e.getResponseBody(), DeserializeSubscription.class);

                    System.out.println(desSub.getMessage().getSubscriptionUID());
                 }
                 catch (JsonParseException e1) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                 }
                 catch (JsonMappingException e1) {
                     System.out.println(e1.getMessage());
                        e.printStackTrace();
                 }
                 catch (IOException e1) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                 }

I've found this solution but I didn't work it https://facingissuesonit.com/2019/07/17/com-fasterxml-jackson-databind-exc-invaliddefinitionexception-cannot-construct-instance-of-xyz-no-creators-like-default-construct-exist-cannot-deserialize-from-object-value-no-delega/

The jackson maven I'm using in my application

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.10.2</version>
    </dependency>

Michał Ziober :

You have to consider few cases:

message field in JSON is primitive String. On POJO level it is an MessageSubscription object.
message value in JSON contains unquoted property names which is illegal but Jackson handles them as well.
If constructor does not fit to JSON we need to configure it using annotations.

To handle unquoted names we need to enable ALLOW_UNQUOTED_FIELD_NAMES feature. To handle mismatch between JSON payload and POJO we need to implement custom deserialiser for MessageSubscription class.

Custom deserialiser could look like this:

class MessageSubscriptionJsonDeserializer extends JsonDeserializer<MessageSubscription> {
    @Override
    public MessageSubscription deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        final String value = p.getValueAsString();
        final Map<String, String> map = deserializeAsMap(value, (ObjectMapper) p.getCodec(), ctxt);

        return new MessageSubscription(map.get("Message"), map.get("SubscriptionUID"));
    }

    private Map<String, String> deserializeAsMap(String value, ObjectMapper mapper, DeserializationContext ctxt) throws IOException {
        final MapType mapType = ctxt.getTypeFactory().constructMapType(Map.class, String.class, String.class);
        return mapper.readValue(value, mapType);
    }
}

Now, we need to customise DeserializeSubscription's constructor:

@Data
class DeserializeSubscription {

    private String code;
    private String reason;
    private MessageSubscription message;

    @JsonCreator
    public DeserializeSubscription(
            @JsonProperty("code") String code,
            @JsonProperty("reason") String reason,
            @JsonProperty("message") @JsonDeserialize(using = MessageSubscriptionJsonDeserializer.class) MessageSubscription message) {
        super();
        this.code = code;
        this.reason = reason;
        this.message = message;
    }
}

Example how to use it:

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.type.MapType;
import lombok.Data;

import java.io.File;
import java.io.IOException;
import java.util.Map;

public class JsonPathApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
        mapper.enable(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES);

        DeserializeSubscription value = mapper.readValue(jsonFile, DeserializeSubscription.class);
        System.out.println(value);
    }
}

For provided JSON payload above example prints:

DeserializeSubscription(code=null, reason=subscription yet available, message=MessageSubscription(message=subscription yet available, subscriptionUID=46b62920-c519-4555-8973-3b28a7a29463))