Classname as a json field

Question

Introduction

I need to serialize a java object (Fahrweg) that contains nested objects (all implement the interface FahrwegEreignis) to json. My code to do this is as follows:

Fahrweg fahrweg = new Fahrweg();

ObjectMapper mapper = new ObjectMapper();

mapper.addMixIn(FahrwegEreignis.class, FahrwegEreignisMixIn.class);

ObjectWriter ow = mapper.writer().withDefaultPrettyPrinter();

try {
  String json = ow.writeValueAsString(fahrweg);
  System.out.print(json);
} catch (JsonProcessingException e) {
  e.printStackTrace();
}

By default, the type of the object is not contained in the resulting json (I assume because JS is dynamically typed).

I would like to add a field to every object about like so: "type" : "classname".

I've read about the Jackson annotations, and I'm using mixin because I cannot modify the classes in question. My mixin interface (FahrwegEreignisMixIn) looks like this:

import com.fasterxml.jackson.annotation.JsonProperty;

public interface FahrwegEreignisMixIn {
    @JsonProperty("type")
    //TODO
}

Question

What do I need to put at //TODO?

My first instinct was Class<?> getClass(); but that doesn't work.

Answer

The answer in the duplicate question worked for me. I had to change my FahrwegEreignisMixIn to this:

import com.fasterxml.jackson.annotation.JsonTypeInfo;

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, property = "type")
public interface FahrwegEreignisMixIn {}

KoenVE · Answer 1 · 2015-12-16T13:16:58.853

0

Have you considered using Google GSon? Works like a charm for me.

Your code would probably look like so:

FahrwegEreignis fahrweg = new Fahrweg();
Gson gson = new Gson();
String json = gson.toJson(fahrweg);

edited Dec 16 '15 at 13:16

answered Dec 16 '15 at 13:14

KoenVE

301
2
11

I'll try this, thanks – Marius Schär Dec 16 '15 at 13:16
1

"Works like a charm" yes, but it doesn't contain the class name either, right? – Sean Patrick Floyd Dec 16 '15 at 13:19
you can use [this](http://stackoverflow.com/a/12117332/3504059) if I'm correct – KoenVE Dec 16 '15 at 13:21
@KoenVE Jackson also supports custom serializers, but due to the large amount of different classes I'd need to write it for I'd rather not do that. – Marius Schär Dec 16 '15 at 13:24

score 0 · Answer 2 · answered Dec 16 '15 at 13:20

0

You can run the following on the instance of the class that implements an interface:

FahrwegEreignisMixInImpl.getClass().getName()

answered Dec 16 '15 at 13:20

aviad

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Classname as a json field

Introduction

Question

Answer

2 Answers2