Sort JsonArray by variable key using GSON

I am trying to sort a JsonArray in Java using GSON, I would like to sort everything inside that array via a variable key, meaning there is a string somewhere containing something that is the key that the object needs to be sorted by.

Key Variable: varkey1

[{"varkey1":1,"othervarkey":1},{"varkey1":6,"othervarkey":2},{"varkey1":3,"othervarkey":3},{"varkey1":12,"othervarkey":4},{"varkey1":998,"othervarkey":5}]

So it should go like like:

[{"varkey1":1,"othervarkey":1},{"varkey1":3,"othervarkey":2},{"varkey1":6,"othervarkey":3},{"varkey1":12,"othervarkey":4},{"varkey1":998,"othervarkey":5}]

Answer

Well, you could just implement a sorting algorithm that could be specialized for Gson JsonElements. If not, you could just re-use standard Collections.sort(...) that can merely do the job for you. For some reason, JsonArray implements Iterable and not List where the latter can be sorted with Collection.sort. So, a custom JsonArray-to-List is required:

final class JsonArrayList
        extends AbstractList<JsonElement> {

    private final JsonArray jsonArray;

    private JsonArrayList(final JsonArray jsonArray) {
        this.jsonArray = jsonArray;
    }

    static List<JsonElement> of(final JsonArray jsonArray) {
        return new JsonArrayList(jsonArray);
    }

    // This method is required when implementing AbstractList
    @Override
    public JsonElement get(final int index) {
        return jsonArray.get(index);
    }

    // This method is required when implementing AbstractList as well
    @Override
    public int size() {
        return jsonArray.size();
    }

    // And this one is required to make the list implementation modifiable
    @Override
    public JsonElement set(final int index, final JsonElement element) {
        return jsonArray.set(index, element);
    }

}

Now, the rest is simple:

// No even need of Gson instantiation
final JsonArray jsonArray = new JsonParser()
        .parse(jsonReader)
        .getAsJsonArray();
// Create a JsonArray to a List view instance
final List<JsonElement> jsonElements = JsonArrays.asList(jsonArray);
// Sorting the jsonElements object
Collections.sort(jsonElements, (e1, e2) -> {
    final int i1 = e1.getAsJsonObject().get("varkey1").getAsInt();
    final int i2 = e2.getAsJsonObject().get("varkey1").getAsInt();
    return Integer.compare(i1, i2);
});

Since the jsonElements is just a view for jsonArray, jsonArray is actually sorted.