bson.ObjectId serialization with gson

Question

I have a class member with type bson.ObjectId.

When serialized, gson by default uses toString() method and the returned value is not what I want. I would like to serialize ObjectId using toHexString() method instead so I could get ObjectId in HexString format.

How do I make gson to serialize ObjectId in HexString format?

Thank you.

Answer 1

I solved the problem. I currently have a class like this to get Gson object and it works well for me.

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

import org.bson.types.ObjectId;

import java.lang.reflect.Type;

public class GsonUtils {

    private static final GsonBuilder gsonBuilder = new GsonBuilder()
            .setDateFormat("yyyy-MM-dd'T'HH:mm:ssZ")
            .registerTypeAdapter(ObjectId.class, new JsonSerializer<ObjectId>() {
                @Override
                public JsonElement serialize(ObjectId src, Type typeOfSrc, JsonSerializationContext context) {
                    return new JsonPrimitive(src.toHexString());
                }
            })
            .registerTypeAdapter(ObjectId.class, new JsonDeserializer<ObjectId>() {
                @Override
                public ObjectId deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
                    return new ObjectId(json.getAsString());
                }
            });

    public static Gson getGson() {
        return gsonBuilder.create();
    }
}

Hope this helps.

Reference: http://max.disposia.org/notes/java-mongodb-id-embedded-document.html

Btw, Reference's code doesn't work and has some minor errros. I fixed those problems in mine.