GSON: How to move fields to parent object

gson, java, json

Solution

You can probably do this by writing, and then registering a custom serializer for `Step`, and making sure inside it you work with `Duration` etc, instead of `Data`.

// registering your custom serializer:
GsonBuilder builder = new GsonBuilder ();
builder.registerTypeAdapter (Step.class, new StepSerializer ());
Gson gson = builder.create ();
// now use 'gson' to do all the work

The code for the custom serializer below, I'm writing off the top of my head. It misses exception handling, and might not compile, and does slow things like create instances of `Gson` repeatedly. But it represents the kind of thing you'll want to do:

class StepSerializer implements JsonSerializer<Step>
{
  public JsonElement serialize (Step src,
                                Type typeOfSrc,
                                JsonSerializationContext context)
    {
      Gson gson = new Gson ();
      /* Whenever Step is serialized,
      serialize the contained Data correctly.  */
      JsonObject step = new JsonObject ();
      step.add ("start_name", gson.toJsonTree (src.start_name);
      step.add ("end_name",   gson.toJsonTree (src.end_name);

      /* Notice how I'm digging 2 levels deep into 'data.' but adding
      JSON elements 1 level deep into 'step' itself.  */
      step.add ("duration",   gson.toJsonTree (src.data.duration);
      step.add ("distance",   gson.toJsonTree (src.data.distance);
      step.add ("location",   gson.toJsonTree (src.data.location);

      return step;
    }
}

Problem

I'm using Google GSON to transform my Java object to JSON. Currently I'm having the following structure: ``` "Step": { "start_name": "Start", "end_name": "End", "data": { "duration": { "value": 292, "text": "4 min." }, "distance": { "value": 1009.0, "text": "1 km" }, "location": { "lat": 59.0000, "lng": 9.0000, "alt": 0.0 } } } ``` Currently a `Duration` object is inside a `Data` object. I would like to skip the `Data` object and move the `Duration` object to the `Step` object, like this: ``` "Step": { "start_name": "Start", "end_name": "End", "duration": { "value": 292, "text": "4 min." }, "distance": { "value": 1009.0, "text": "1 km" }, "location": { "lat": 59.0000, "lng": 9.0000, "alt": 0.0 } } ``` How can I do this using GSON? EDIT: I've tried to use a TypeAdapter to modify the Step.class, but in the write-method I'm not able to add my duration object to the JsonWriter.

Original source