Json and abstract class 'Can not construct instance'

Question

I have read a lot about this problem on stackoverflow but any solution works for me. Could anybody please tell me why it's not working since I have described all children object properly - or maybe not ?

This are my dependency for jackson

<context:annotation-config/>    
<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-mapper-asl</artifactId>
    <version>1.9.10</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.3.2</version>
</dependency>

Main class with my abstract object as property (MLMObject)

public class MLMResponse {

    private int errorCode;
    private String errorMessage;
    private MLMObject object;


    public MLMResponse() {

    }


    public int getErrorCode() {
        return errorCode;
    }
    public void setErrorCode(int errorCode) {
        this.errorCode = errorCode;
    }
    public String getErrorMessage() {
        return errorMessage;
    }
    public void setErrorMessage(String errorMessage) {
        this.errorMessage = errorMessage;
    }
    public MLMObject getObject() {
        return object;
    }
    public void setObject(MLMObject object) {
        this.object = object;
    }



}

abstract class implementation

import com.fasterxml.jackson.annotation.*;



@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(value=Person.class, name="person"),
        })
public abstract class MLMObject {

    public MLMObject() {
        super();        
    }


}

Child class implementation

import com.fasterxml.jackson.annotation.JsonTypeName;


@JsonTypeName("person")
public class Person extends MLMObject{

    private String name;
    private String secondName;


    public Person() {
        super();
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSecondName() {
        return secondName;
    }
    public void setSecondName(String secondName) {
        this.secondName = secondName;
    }




}

and json text I'm going to read - this is only test for real message.

String msg = "{\"errorCode\": 0,\"errorMessage\":\"\",\"object\":{\"type\":\"person\",\"name\":\"Jan\",\"secondName\":\"Jan\"}}";

I'm trying to read it with following code

ObjectMapper objectMapper = new ObjectMapper();
 MLMResponse emp = objectMapper.readValue(msg, MLMResponse.class);

But when I run it I'm getting following error.

org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.pl.model.MLMObject, problem: abstract types can only be instantiated with additional type information
 at [Source: java.io.StringReader@a06816; line: 1, column: 34] (through reference chain: com.pl.model.MLMResponse["object"])
    at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:163)
    at org.codehaus.jackson.map.deser.StdDeserializationContext.instantiationException(StdDeserializationContext.java:233)
    at org.codehaus.jackson.map.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:60)
    at org.codehaus.jackson.map.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:299)
    at org.codehaus.jackson.map.deser.SettableBeanProperty$MethodProperty.deserializeAndSet(SettableBeanProperty.java:414)
    at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:697)
    at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:580)
    at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2732)
    at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1863)
    at com.pl.service.JacksonMappingService.mapLoginMessage(JacksonMappingService.java:22)
    at com.pl.controller.HelloWorldController.hello(HelloWorldController.java:38)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)

Could anybody please help me with that ?

Regards Jan

Answer 1

Synchronize your Jackson versions. Jackson 1 looks for Jackson 1 annotations and Jackson 2 looks for Jackson 2 annotations. You are trying to have Jackson 1 look for Jackson 2 annotations. This simply won't work.