Question

I am developing a REST interface for my app using Jackson to serialize my POJO domain objects to JSON representation. I want to customize the serialization for some types to add additional properties to the JSON representation that do not exist in POJOs (e.g. add some metadata, reference data, etc). I know how to write my own JsonSerializer, but in that case I would need to explicitly call JsonGenerator.writeXXX(..) methods for each property of my object while all I need is just to add an additional property. In other words I would like to be able to write something like:

@Override
public void serialize(TaxonomyNode value, JsonGenerator jgen, SerializerProvider provider) {
    jgen.writeStartObject();
    jgen.writeAllFields(value); // <-- The method I'd like to have
    jgen.writeObjectField("my_extra_field", "some data");
    jgen.writeEndObject();
}

or (even better) to somehow intercept the serialization before the jgen.writeEndObject() call, e.g.:

@Override void beforeEndObject(....) {
    jgen.writeObjectField("my_extra_field", "some data");
}

I thought I could extend BeanSerializer and override its serialize(..) method but it’s declared final and also I couldn’t find an easy way to create a new instance of BeanSerializer without providing it with all the type metadata details practically duplicating a good portion of Jackson. So I’ve given up on doing that.

My question is – how to customize Jackson’s serialization to add additional stuff to the JSON output for particular POJOs without introducing too much of the boilerplate code and reusing as much as possible of the default Jackson behaviour.

Answer 1

After looking more on the Jackson source code I concluded that it’s simply impossible to achieve without writing my own BeanSerializer, BeanSerializerBuilder and BeanSerializerFactory and provide some extension points like:

/*
/**********************************************************
/* Extension points
/**********************************************************
 */

protected void beforeEndObject(T bean, JsonGenerator jgen, SerializerProvider provider) throws IOException, JSONException {
    // May be overridden
}

protected void afterStartObject(T bean, JsonGenerator jgen, SerializerProvider provider) throws IOException, JSONException {
    // May be overridden
}

Unfortunately I had to copy and paste entire Jackson‘s BeanSerializer source code to MyCustomBeanSerializer because the former is not developed for extensions declaring all the fields and some important methods (like serialize(...)) as final