Serialize Realm objects to JSON using GSON

SerializeToJson.java

// GSON can parse the data.
//
// Deserialization:
// Note there is a bug in GSON 2.3.1 that can cause it to StackOverflow when working with RealmObjects.
// To work around this, use the ExclusionStrategy below or downgrade to 1.7.1
// See more here: https://code.google.com/p/google-gson/issues/detail?id=440
//
// Serialization:
// <Type>RealmProxy objects are created by the Realm annotation processor. They are used to control
// access to the actual data instead of storing them in fields and it is therefore them we need to register a
// TypeAdapter for.
Gson gson = new GsonBuilder()
        .setExclusionStrategies(new ExclusionStrategy() {
            @Override
            public boolean shouldSkipField(FieldAttributes f) {
                return f.getDeclaringClass().equals(RealmObject.class);
            }

            @Override
            public boolean shouldSkipClass(Class<?> clazz) {
                return false;
            }
        })
        .registerTypeAdapter(Class.forName("io.realm.PersonRealmProxy"), new PersonSerializer())
        .registerTypeAdapter(Class.forName("io.realm.DogRealmProxy"), new DogSerializer())
        .create();

// Serialize a Realm object to a JSON string
String json = gson.toJson(realm.where(Person.class).findFirst());

Dog.java

package io.realm.example;

import io.realm.RealmObject;

public class Dog extends RealmObject {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

DogSerializer.java

package io.realm.examples;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

import java.lang.reflect.Type;

import io.realm.examples.realmgridview.Dog;

public class DogSerializer implements JsonSerializer<Dog> {

    @Override
    public JsonElement serialize(Dog src, Type typeOfSrc, JsonSerializationContext context) {
        final JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("name", src.getName());
        return jsonObject;
    }
}

Person.java

package io.realm.example;

import io.realm.RealmList;
import io.realm.RealmObject;

public class Person extends RealmObject {

    private String name;
    private int age;
    private Dog favoriteDog;
    private RealmList<Dog> dogs;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Dog getFavoriteDog() {
        return favoriteDog;
    }

    public void setFavoriteDog(Dog favoriteDog) {
        this.favoriteDog = favoriteDog;
    }

    public RealmList<Dog> getDogs() {
        return dogs;
    }

    public void setDogs(RealmList<Dog> dogs) {
        this.dogs = dogs;
    }
}

PersonSerializer.java

package io.realm.example;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

import java.lang.reflect.Type;

public class PersonSerializer implements JsonSerializer<Person> {

    @Override
    public JsonElement serialize(Person src, Type typeOfSrc, JsonSerializationContext context) {
        final JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("name", src.getName());
        jsonObject.addProperty("age", src.getAge());
        jsonObject.add("favoriteDog", context.serialize(src.getFavoriteDog()));
        jsonObject.add("dogs", context.serialize(src.getDogs()));
        return jsonObject;
    }
}

Hi:
I have checked this and it is not working when I was trying to set directly the dog object. Checking on Google I found that for directly access you must register the type adapter for the dog class directly like this:

gsonBuilder.registerTypeAdapter(Dog.class, new DogSerializer());
gsonBuilder.registerTypeAdapter(Person.class, new PersonSerializer())

Source:
https://gist.github.com/Retistic/9afece43e3d01f017f8b

I had to do more work than what you show here to serialize a RealmList. The code jsonObject.add("dogs", context.serialize(src.getDogs())); was not enough (it did not work properly: was setting the fields to columnInfo, someIndex...).

To serialize a RealmList I used this in my JsonSerializer<>:

JsonArray dogs = new JsonArray();
for (Dog dog : src.getDogs()) {
    // Note: it does not work if you don't pass Dog.class
    dogs.add(context.serialize(dog, Dog.class));
}
jsonObject.add("dogs", dogs);

👍

For RealmList, it can be done like this:

jsonObject.add("dogs", context.serialize(src.getDogs().toArray(), Dog[].class));

@jiahaoliuliu it should work. I think you may used that "io.realm.DogRealmProxy" in the above gist but you should replace that part with your package name. Class.forName() helps you to prevent importing unnecessary classes in your class just for getting their class instance. although in my case I need those classes actually in my activity so I imported those and used them like what you did. thanks to you.

I have written the script to generate Serializer classes. No need to manually write these dumb classes.

Gist link

gsonBuilder.registerTypeAdapter(DogRealmProxy.class, new DogSerializer());
gsonBuilder.registerTypeAdapter(PersonRealmProxy.class, new PersonSerializer())

Works just fine

For those who still has troubles with serialization:

Your model:

public class User extends RealmObject {
@PrimaryKey
    private String id;
    private String name;
    private String email;

    // getters and setters
}

Your UserSerializer:

public class UserSerializer implements JsonSerializer<User> {

    @Override
    public JsonElement serialize(User src, Type typeOfSrc, JsonSerializationContext context) {
        final JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("id", src.getId());
        jsonObject.addProperty("email", src.getEmail());
        jsonObject.addProperty("name", src.getName());
    }
}

Your method where you call e.g. retrofit interface:

...
    private UserApi api;
...
    @Override
    public void updateUser(String name, String info, String photoUrl) {
        User user = realm.copyFromRealm(current); // make copy of the model from realm
        user.setName(name);
        user.setInfo(info);
        user.setPhoto(photoUrl);
        api.updateUser(user);
        ...
}

Your Gson configuration:

new GsonBuilder()
                .setExclusionStrategies(new ExclusionStrategy() {
                    @Override
                    public boolean shouldSkipField(FieldAttributes f) {
                        return f.getDeclaringClass().equals(RealmObject.class);
                    }

                    @Override
                    public boolean shouldSkipClass(Class<?> clazz) {
                        return false;
                    }
                })
                .registerTypeAdapter(User.class, new UserSerializer())
                .create();

profit.

The more i use realm, the more reasons i keep finding not to use it.
Yes, you don't have to write boilerplate SQL but you introduce new boilerplate and workarounds.

@cmelchior this doesn't work with Realm-1.1.0 and Retrofit2-2.1.0. Not sure if to create issue for realm or retrofit

@cmelchior also experiencing this issue...

Update:
this is in fact working with realm 1.1.1; exactly as it is demonstrated. i was using my model class when registering the adapter instead of realm's proxy class for the model.

@ArthurSav meh, to serialize with GSON, just call gson.toJson(realm.copyFromRealm(realmObject));

@ArthurSav I find it incredibly creepy that I was thinking exactly the same thing right before reading your comment.....

gson.toJson(realm.copyFromRealm(realmObject)); return a JsonObject? How i can do that? @Zhuinden

@felixeduardo15

copyFromRealm will return a unmanaged object/objects, so you can use it directly with no realm exception.
gson.toJson(realm.copyFromRealm(realmObject/realmObjects)); is a lazy function but it worked.

I am using this and it actually works with me:

Gson gson = new Gson();
String listString = gson.toJson(
    items,
    new TypeToken<ArrayList<Item>>() {}.getType());
try {
    JSONArray jsonArray =  new JSONArray(listString);
    System.out.println(jsonArray.toString());
} catch (JSONException e) {
    e.printStackTrace();
}