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Realm, GSON and primitive JSON arrays
// Make a custom Gson instance, with a custom TypeAdapter for each wrapper object.
// In this instance we only have RealmList<RealmInt> as a a wrapper for RealmList<Integer>
Type token = new TypeToken<RealmList<RealmInt>>(){}.getType();
Gson gson = new GsonBuilder()
.setExclusionStrategies(new ExclusionStrategy() {
public boolean shouldSkipField(FieldAttributes f) {
return f.getDeclaringClass().equals(RealmObject.class);
public boolean shouldSkipClass(Class<?> clazz) {
return false;
.registerTypeAdapter(token, new TypeAdapter<RealmList<RealmInt>>() {
public void write(JsonWriter out, RealmList<RealmInt> value) throws IOException {
// Ignore
public RealmList<RealmInt> read(JsonReader in) throws IOException {
RealmList<RealmInt> list = new RealmList<RealmInt>();
while (in.hasNext()) {
list.add(new RealmInt(in.nextInt()));
return list;
// Convert JSON to objects as normal
List<MainObject> objects = gson.fromJson(json, new TypeToken<List<MainObject>>(){}.getType());
// Copy objects to Realm
{ "name" : "Foo",
"ints" : [1, 2, 3]
{ "name" : "Bar",
"ints" : []
public class MainObject extends RealmObject {
private String name;
private RealmList<RealmInt> ints;
// Getters and setters
public class RealmInt extends RealmObject {
private int val;
public RealmInt() {
public RealmInt(int val) {
this.val = val;
// Getters and setters

jemshit commented Sep 9, 2016 edited

Don't we need to define primary key for RealmInt ? so it does not overwrite. Consider i have two RealmList in Model and they have same values, then i want to change one of the list's value and leave other RealmList same, is this possible with this implementation? @cmelchior

koocbor commented Sep 23, 2016

if the primitive array can be null you might want to add this check to your read method:

if (in.peek() == JsonToken.NULL) {
   return null;

This was very helpful, thank you.


@cmelchior any workaround if we use realm.createOrUpdateObjectFromJson(RecipeRealmObject.class, jsonObject) method.
I am getting the following exception:
org.json.JSONException: Value Sätt ugnen på knappt 225 grader. Smörj en ugnsfast form som ska vara så liten att fiskblocket ligger trångt och ha kanter som går minst någon cm över fiskens höjd. at 0 of type java.lang.String cannot be converted to JSONObject
at org.json.JSON.typeMismatch(

I have a json object as : {"recipe":{ "name":"Recipe name", cookingSteps": [
"Sätt ugnen på 175 grader.",
"Lägg kycklingfiléerna i en ugnsfast form. \r\nBlanda ihop ingredienserna till såsen och häll sedan över kycklingen.",
"Laga i mitten av ugnen i ca. 60 min.\r\n\r\nFantastiskt enkelt och gott:)"

Any help would be greatly appreciated.

Joisar commented Jun 20, 2017

I am facing the same problem about java.lang.String cannot be converted to JSONObject
at org.json.JSON.typeMismatch(

any workaround?

Joisar commented Jun 21, 2017

@cmelchior, @RajendraSinghBohra : I have created a solution which will work fine without having issue as mentioned in previous comments.

VivekNeel commented Jul 11, 2017 edited

How can this be used for ArrayList<ArrayList> ?

I have a field like this : @SerializedName("matches") private ArrayList<ArrayList> matches;

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