Using GSON do not parse a field, only keep it with the json raw string

Question

Using GSON in Java is there any annotation where I can indicate a field that it should keep it as a raw string even though it is an object. ?

Or What would be the easiest way to achieve this?

//This is the original
    @SerializedName("perro")
    public Perro perro

//This is what I want to achieve 
    @SerializedName("perro")
    public String perro

So the result should be 
perro = "{"Users":[{"Name":"firulais","Raza":"beagle"},{"Name":"Spike","Value":"Terrier"}]}"

Samurai

I don't understand. A Java String will be serialized as a JSON string. Can you clarify with an example? – Unmoor

So say I have a Java Class call Animal.java that has many fields one of the fields is call Perro which an Object, so If I have a String response that it is actually a JSON , then if I do something like Animal animal = gson.fromJson(response,Animal.class), then I want the Perro field to be kept as the json raw string and not parse it into the Perro object. – Samurai

Please edit your question with an example JSON payload. If your field is of type Object and it's actually a JSON string in the JSON, I believe Gson will fail to parse. If it's Object, Gson expects a JSON object. – Unmoor

So the field of type Object I want it to be type of String, to not parse that field and just keep the raw Json string specific of that field – Samurai

Answer 1

The only way I found this to work was using

public JsonElement perro;

Samurai

Thanks, this is exactly what I was looking for! – Wendall

Although this works, it uses a ton of memory because JsonElement keeps the entire json structure in memory as a tree. – Wendall

Answer 2

Based on @mrsegev's answer, here's a simpler version (in Kotlin) that works with arbitrary objects:

class RawJsonAdapter: TypeAdapter<String>() {
    override fun write(out: JsonWriter?, value: String?) {
        out?.jsonValue(value)
    }
    override fun read(reader: JsonReader?): String {
        return JsonParser().parse(reader).toString()
    }
}

This takes advantage of JsonWriter#jsonValue() which was added in https://github.com/google/gson/pull/667

Usage:

@JsonAdapter(RawJsonAdapter::class)
val fieldName: String? = null

Wendall

There is an updated version in github.com/google/gson/issues/1368#issuecomment-417821473 – Wendall

For the equivalent in moshi, see github.com/square/moshi/issues/675#issuecomment-842732058 – Wendall

Answer 3

Basically speaking, You need to create a custom gson TypeAdapter class and write the conversion login from Object to String yourself.

Then annotate the field indicating what TypeAdapter to use in order to read/write it using gson.

More details in this blog post: Gson TypeAdapter Example

Example: Prasing class object as a raw JSON string

public class StringTypeAdapter extends TypeAdapter<String> {

    @Override
    public void write(JsonWriter out, String value) throws IOException {
        try {
            JSONObject jsonObject = new JSONObject(value);
            out.beginObject();
            Iterator<String> iterator = jsonObject.keys();
            while (iterator.hasNext()) {
                String key = iterator.next();
                String keyValue = jsonObject.getString(key);
                out.name(key).value(keyValue);
            }
            out.endObject();
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    @Override
    public String read(JsonReader in) throws IOException {
        in.beginObject();
        JSONObject jsonObject = new JSONObject();
        while (in.hasNext()) {
            final String name = in.nextName();
            final String value = in.nextString();
            try {
                jsonObject.put(name, value);
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
        in.endObject();
        return jsonObject.toString();
    }
}

Using the TypeAdapter:

@JsonAdapter(StringTypeAdapter.class)
private String someClass; // Lazy parsing this json

Benioff

I tried using the TypeAdapter but how to convert the JsonReader in, to the original string? – Samurai

Updated my answer with an example to parse class object as a raw JSON string. – Benioff

This one did not work, while is reading if there is a JSONObject as a string then it gets an exception – Samurai

FYI, the write() method of the TypeAdapter can use jsonValue() to emit raw json directly. See github.com/google/gson/pull/667 – Wendall

Answer 4

You should be able to use public JsonObject perro;

You can then call gson.toJson(perro) to get the String value.

Segregation

I tried using @SerializedName("perro") public JsonObject perro but does not work – Samurai

@KenenisaBekele can you include full json string you're converting...I'm using the approach I mentioned in my answer in a few places where a field in json payload contains another json string.....but perhaps what you have isn't quite this case. – Civics

There's no reason to involve a Gson instance again. Just use perro.toString() to get the String representation. – Unmoor

@KenenisaBekele Why this answer is downvoted. This is a good solution without a custom type adapter. – Therefore

does not work Expected a com.google.gson.JsonObject but was com.google.gson.JsonPrimitive – Samurai