Question

I am trying to deserialize a JSON String like (extracted this bit to show the issue)

{
    "$type": "com.example.StringProperty",
    "value": "hello world",
    "name": "text",
    "readOnly": false
}

into a hierarchy of classes that look like

public class Property
{
    public String name;
    public int    type;

    Property(String pName, int pType) { name = pName; type = pType; }
}

public class StringProperty extends Property 
{
    public String value;        
    StringProperty(String pName, String pValue) {
        super(pName, String);
        value = pValue;
    }       
}

using the following mixin annotations

@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS, include=JsonTypeInfo.As.PROPERTY, property="$type")
abstract public class PropertyMixin
{
    @JsonProperty
    public String name;
    //@JsonIgnore
    //public boolean readOnly;
    @JsonProperty
    public int type;

    PropertyMixin(@JsonProperty("name") String pName, @JsonProperty("type") int pType)
    {
    }
}

abstract public class StringPropertyMixin
{
    @JsonProperty
    public String value;
    //@JsonIgnore
    //public boolean readOnly;

    @JsonCreator
    public StringPropertyMixin(@JsonProperty("name") String pName, @JsonProperty("value") String value)
    {
    }
}

With Jackson 1.9.2, the error I am getting is

Unrecognized field "readOnly" (Class com.example.StringProperty), not marked as ignorable

I tried using @JsonIgnore, but that did not help (check the locations of the code I commented out to see how I tried it). I am probably missing something, but I think another set of eyes need to look at it and help me.

This is how the deserialization environment looks like:

        objectMapper.setVisibilityChecker(objectMapper.getSerializationConfig().getDefaultVisibilityChecker()
                .withFieldVisibility(JsonAutoDetect.Visibility.NONE)
                .withGetterVisibility(JsonAutoDetect.Visibility.NONE)
                .withSetterVisibility(JsonAutoDetect.Visibility.NONE)
                .withCreatorVisibility(JsonAutoDetect.Visibility.NONE));

        MixinRegistrations module = new MixinRegistrations();
        objectMapper.registerModule(module);

and mixin module looks like

@Override
public void setupModule(SetupContext context)
{
    context.setMixInAnnotations(Property.class, PropertyMixin.class);
    context.setMixInAnnotations(StringProperty.class, StringPropertyMixin.class);
}

I appreciate all the help. Thanks in advance.

PS: I do not know if this makes a difference but the JSON is being generated by a library written in .Net Framework v4.

Answer 1

I believe Jackson is having problems because the method that you have delegated as a creator does not have a parameter for the readOnly field. So rather than silently ignore this missing parameter Jackson is throwing an error (good behaviour). Try using the JsonIgnoreProperties annotation. I’ve not had need to use if before, but for deserialisation you can explicitly denote fields that are not required by the creator.

Oh, this appears related as well.

Edit:
Another question that the asker found that was useful.