how to only serialize properties annotated with a custom annotation

Question

We use jackson throughout our application to serialize and deserialize Java objects to JSON. It works great.

Is it possible, perhaps through a custom serializer, to serialize only properties of a Java object that are Annotated with a custom annotation?

So, given the custom annotation:

public @interface SpecialField {}

And the following bean

public SomeBean {
   @SpecialField
   private Object propertyIncluded;

   private Object propertyExcluded;
}

What would a custom serializer (or some equivalent mechanism) look like to serialize propertyIncluded (using the normal jackson object mapper) and ignore propertyExcluded?

We can't use standard jackson annotations (@JsonIgnore) in this use case because it would break our other serialization uses cases in the application.

Answer 1

While this might not be quite what your looking for, It is possible to make the jackson engine serialize objects differently via some tweaking. In my example below I create two types of serializers which will or wont serialize a field marked as transient.

import java.io.Serializable;

import org.codehaus.jackson.annotate.JsonAutoDetect;
import org.codehaus.jackson.map.ObjectMapper;

public class Test {

    public static void main(String[] args) throws Exception {
        ISerializer d = new Doesnt();
        ISerializer o = new Observes();

        SomeObject obj = new SomeObject();

        System.out.println("Doesnt: " + d.serialize(obj));

        System.out.println("Observes: " + o.serialize(obj));
    }
    public static class Doesnt implements ISerializer<SomeObject> {

        @Override
        public String serialize(SomeObject o) throws Exception {
            ObjectMapper om = new ObjectMapper();
            om.setVisibilityChecker(
                    om.getSerializationConfig().
                    getDefaultVisibilityChecker().
                    withFieldVisibility(JsonAutoDetect.Visibility.ANY).
                    withGetterVisibility(JsonAutoDetect.Visibility.ANY));
            return om.writeValueAsString(o);
        }

    }

    public static class Observes implements ISerializer<SomeObject> {

        @Override
        public String serialize(SomeObject o) throws Exception {
            ObjectMapper om = new ObjectMapper();
            om.setVisibilityChecker(
                    om.getSerializationConfig().
                    getDefaultVisibilityChecker().
                    withFieldVisibility(JsonAutoDetect.Visibility.ANY).
                    withGetterVisibility(JsonAutoDetect.Visibility.NONE));
            return om.writeValueAsString(o);
        }       
    }
    public interface ISerializer<T> {
        public String serialize(T o) throws Exception;
    }

    public static class SomeObject implements Serializable {
        private static final long serialVersionUID = 745063791749142843L;
        private transient String myVar = "Transient";
        private String myOther = "Not Transient";
        public String getMyVar() {
            return myVar;
        }
        public void setMyVar(String myVar) {
            this.myVar = myVar;
        }
        public String getMyOther() {
            return myOther;
        }
        public void setMyOther(String myOther) {
            this.myOther = myOther;
        }
    }
}

output:

Doesnt: {"myVar":"Transient","myOther":"Not Transient"}
Observes: {"myOther":"Not Transient"}

I would think it would be fairly easy to change serializers to extend the JsonSerializer class, and do something similar in them.