RealmList JsonAdapter for Moshi. Based on CollectionJsonAdapter: https://github.com/square/moshi/blob/master/moshi/src/main/java/com/squareup/moshi/CollectionJsonAdapter.java

RealmListJsonAdapter.java

import com.squareup.moshi.JsonAdapter;
import com.squareup.moshi.JsonReader;
import com.squareup.moshi.JsonWriter;
import com.squareup.moshi.Moshi;
import com.squareup.moshi.Types;
import io.realm.RealmList;
import io.realm.RealmModel;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.util.Collection;
import java.util.Set;

public class RealmListJsonAdapter<T extends RealmModel> extends JsonAdapter<RealmList<T>> {

  public static final JsonAdapter.Factory FACTORY = new JsonAdapter.Factory() {
    @Override public JsonAdapter<?> create(
        Type type, Set<? extends Annotation> annotations, Moshi moshi) {
      Class<?> rawType = Types.getRawType(type);
      if (!annotations.isEmpty()) return null;
      if (rawType == RealmList.class) {
        return newRealmListAdapter(type, moshi).nullSafe();
      }
      return null;
    }
  };

  private final JsonAdapter<T> elementAdapter;

  public RealmListJsonAdapter(JsonAdapter<T> elementAdapter) {
    this.elementAdapter = elementAdapter;
  }

  RealmList<T> newRealmList() {
    return new RealmList<T>();
  }

  private static <T extends RealmModel> JsonAdapter<RealmList<T>> newRealmListAdapter(Type type, Moshi moshi) {
    Type elementType = Types.collectionElementType(type, Collection.class);
    JsonAdapter<T> elementAdapter = moshi.adapter(elementType);
    return new RealmListJsonAdapter<T>(elementAdapter);
  }

  @Override public RealmList<T> fromJson(JsonReader reader) throws IOException {
    RealmList<T> result = newRealmList();
    reader.beginArray();
    while (reader.hasNext()) {
      result.add(elementAdapter.fromJson(reader));
    }
    reader.endArray();
    return result;
  }

  @Override public void toJson(JsonWriter writer, RealmList<T> value) throws IOException {
    writer.beginArray();
    for (T element : value) {
      elementAdapter.toJson(writer, element);
    }
    writer.endArray();
  }

  @Override public String toString() {
    return elementAdapter + ".realmList()";
  }
}