Custom Jackson Serializer for a specific type in a particular class

Is there a way by which Jackson allows custom serialization for a specific type only in a particular class?

Here is my scenario: I have ClassA.java which is something like:

public Class ClassA {

    byte[] token;
    String name;

    public getToken() {
        return token;
    }

    public setToken(byte[] newToken) {
        token = newToken;
    }

    public getName() {
        return name;
    }

    public setName(String newName) {
        name = newName;
    }
}

I do not have access to this class as it is in an external jar. However, I want to serialize the token byte array here in a particular manner. I have created a Custom serializer that does that and tries adding it to the mapper in all the ways mentioned in Jackson docs.

public class ByteArrayJacksonSerializer extends JsonSerializer<byte[]> {

    public void serialize(byte[] value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {

        String token = doMyThing(value);
        jgen.writeString(token);
    }
}

And in mapper, something like this:

public class MyObjectMapper extends ObjectMapper {

    CustomSerializerFactory sf = new CustomSerializerFactory();
    sf.addGenericMapping(byte[].class, new ByteArrayJacksonSerializer());
    this.setSerializerFactory(sf);

    and some more code here...
}

However I can do it only for byte[] in general, and not for ONLY byte[] in ClassA. Is there a way to let Jackson know that this custom serializer must be used ONLY for fields of byte[] type in ClassA, and to do serialization it's own way for all other classes?

Solution 1:

You should use MixIn feature. In your example you have to create new interface:

interface ClassAMixIn {

    @JsonSerialize(using = ByteArrayJacksonSerializer.class)
    byte[] getToken();
}

which specifies custom serializer for given property. Now we have to configure ObjectMapper

ObjectMapper mapper = new ObjectMapper();
mapper.addMixInAnnotations(ClassA.class, ClassAMixIn.class);

Your custom serializer will be used only for serializing byte array property in ClassA.