Stream quiz JSON parsing on background executor

app/src/main/java/com/d4rk/androidtutorials/java/data/repository/DefaultQuizRepository.java

@@ -1,10 +1,7 @@
 package com.d4rk.androidtutorials.java.data.repository;
 
-import com.d4rk.androidtutorials.java.data.model.QuizQuestion;
 import com.d4rk.androidtutorials.java.data.source.QuizLocalDataSource;
 
-import java.util.List;
-
 /**
  * Default implementation of {@link QuizRepository} using a local data source.
  */
@@ -17,7 +14,7 @@ public DefaultQuizRepository(QuizLocalDataSource localDataSource) {
     }
 
     @Override
-    public List<QuizQuestion> loadQuestions() {
-        return localDataSource.loadQuestions();
+    public void loadQuestions(QuestionsCallback callback) {
+        localDataSource.loadQuestions(callback::onResult);
     }
 }

app/src/main/java/com/d4rk/androidtutorials/java/data/repository/QuizRepository.java

@@ -8,5 +8,10 @@
  * Abstraction over quiz data operations.
  */
 public interface QuizRepository {
-    List<QuizQuestion> loadQuestions();
+
+    interface QuestionsCallback {
+        void onResult(List<QuizQuestion> questions);
+    }
+
+    void loadQuestions(QuestionsCallback callback);
 }

app/src/main/java/com/d4rk/androidtutorials/java/data/source/DefaultQuizLocalDataSource.java

@@ -4,50 +4,70 @@
 
 import com.d4rk.androidtutorials.java.data.model.QuizQuestion;
 
-import org.json.JSONArray;
-import org.json.JSONException;
-import org.json.JSONObject;
+import android.util.JsonReader;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.InputStreamReader;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.concurrent.ExecutorService;
 
 /**
  * Reads quiz questions from the assets folder.
  */
 public class DefaultQuizLocalDataSource implements QuizLocalDataSource {
 
     private final AssetManager assetManager;
+    private final ExecutorService executorService;
 
-    public DefaultQuizLocalDataSource(AssetManager assetManager) {
+    public DefaultQuizLocalDataSource(AssetManager assetManager, ExecutorService executorService) {
         this.assetManager = assetManager;
+        this.executorService = executorService;
     }
 
     @Override
-    public List<QuizQuestion> loadQuestions() {
-        try (InputStream is = assetManager.open("quiz_questions.json")) {
-            byte[] buffer = new byte[is.available()];
-            int read = is.read(buffer);
-            String json = new String(buffer, 0, read, StandardCharsets.UTF_8);
-            JSONArray array = new JSONArray(json);
+    public void loadQuestions(QuestionsCallback callback) {
+        executorService.execute(() -> {
             List<QuizQuestion> result = new ArrayList<>();
-            for (int i = 0; i < array.length(); i++) {
-                JSONObject obj = array.getJSONObject(i);
-                String question = obj.getString("question");
-                JSONArray opts = obj.getJSONArray("options");
-                String[] options = new String[opts.length()];
-                for (int j = 0; j < opts.length(); j++) {
-                    options[j] = opts.getString(j);
+            try (InputStream is = assetManager.open("quiz_questions.json");
+                 JsonReader reader = new JsonReader(new InputStreamReader(is, StandardCharsets.UTF_8))) {
+                reader.beginArray();
+                while (reader.hasNext()) {
+                    reader.beginObject();
+                    String question = null;
+                    List<String> options = new ArrayList<>();
+                    int answer = -1;
+                    while (reader.hasNext()) {
+                        String name = reader.nextName();
+                        switch (name) {
+                            case "question" -> question = reader.nextString();
+                            case "options" -> {
+                                reader.beginArray();
+                                while (reader.hasNext()) {
+                                    options.add(reader.nextString());
+                                }
+                                reader.endArray();
+                            }
+                            case "answer" -> answer = reader.nextInt();
+                            default -> reader.skipValue();
+                        }
+                    }
+                    reader.endObject();
+                    if (question != null && !options.isEmpty() && answer >= 0) {
+                        result.add(new QuizQuestion(
+                                question,
+                                options.toArray(new String[0]),
+                                answer));
+                    }
                 }
-                int answer = obj.getInt("answer");
-                result.add(new QuizQuestion(question, options, answer));
+                reader.endArray();
+            } catch (IOException e) {
+                result = Collections.emptyList();
             }
-            return result;
-        } catch (IOException | JSONException e) {
-            return Collections.emptyList();
-        }
+            callback.onResult(result);
+        });
     }
 }

app/src/main/java/com/d4rk/androidtutorials/java/data/source/QuizLocalDataSource.java

@@ -8,5 +8,10 @@
  * Contract for reading quiz data from local storage.
  */
 public interface QuizLocalDataSource {
-    List<QuizQuestion> loadQuestions();
+
+    interface QuestionsCallback {
+        void onResult(List<QuizQuestion> questions);
+    }
+
+    void loadQuestions(QuestionsCallback callback);
 }

app/src/main/java/com/d4rk/androidtutorials/java/di/AppModule.java

@@ -224,9 +224,9 @@ public SetConsentAcceptedUseCase provideSetConsentAcceptedUseCase(SettingsReposi
 
     @Provides
     @Singleton
-    public QuizLocalDataSource provideQuizLocalDataSource(Application application) {
+    public QuizLocalDataSource provideQuizLocalDataSource(Application application, ExecutorService executorService) {
         AssetManager manager = application.getAssets();
-        return new DefaultQuizLocalDataSource(manager);
+        return new DefaultQuizLocalDataSource(manager, executorService);
     }
 
     @Provides

app/src/main/java/com/d4rk/androidtutorials/java/domain/quiz/LoadQuizQuestionsUseCase.java

@@ -2,17 +2,22 @@
 
 import com.d4rk.androidtutorials.java.data.model.QuizQuestion;
 import com.d4rk.androidtutorials.java.data.repository.QuizRepository;
+
 import java.util.List;
 
 /** Loads quiz questions from assets. */
 public class LoadQuizQuestionsUseCase {
     private final QuizRepository repository;
 
+    public interface Callback {
+        void onResult(List<QuizQuestion> questions);
+    }
+
     public LoadQuizQuestionsUseCase(QuizRepository repository) {
         this.repository = repository;
     }
 
-    public List<QuizQuestion> invoke() {
-        return repository.loadQuestions();
+    public void invoke(Callback callback) {
+        repository.loadQuestions(callback::onResult);
     }
 }

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/android/lessons/buttons/buttons/tabs/ButtonsTabLayoutFragment.java

@@ -20,8 +20,10 @@
 import com.d4rk.androidtutorials.java.utils.FontManager;
 import com.google.android.gms.ads.AdRequest;
 
+import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.InputStreamReader;
 import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.Map;
@@ -61,14 +63,15 @@ public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
         for (Map.Entry<Integer, CodeView> entry : buttonXMLResources.entrySet()) {
             Integer resourceId = entry.getKey();
             CodeView codeView = entry.getValue();
-            try (InputStream inputStream = getResources().openRawResource(resourceId)) {
-                byte[] bytes = new byte[inputStream.available()];
-                int result = inputStream.read(bytes);
-                if (result != -1) {
-                    String text = new String(bytes, StandardCharsets.UTF_8);
-                    codeView.setText(text);
-                    CodeHighlighter.applyXmlTheme(codeView);
+            try (InputStream inputStream = getResources().openRawResource(resourceId);
+                 BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8))) {
+                StringBuilder builder = new StringBuilder();
+                String line;
+                while ((line = reader.readLine()) != null) {
+                    builder.append(line).append('\n');
                 }
+                codeView.setText(builder.toString());
+                CodeHighlighter.applyXmlTheme(codeView);
             } catch (IOException e) {
                 Log.e("ButtonsTab", "Error reading button resource", e);
             }

app/src/main/java/com/d4rk/androidtutorials/java/ui/screens/quiz/QuizViewModel.java

@@ -7,6 +7,7 @@
 import com.d4rk.androidtutorials.java.data.model.QuizQuestion;
 import com.d4rk.androidtutorials.java.domain.quiz.LoadQuizQuestionsUseCase;
 
+import java.util.Collections;
 import java.util.List;
 
 import dagger.hilt.android.lifecycle.HiltViewModel;
@@ -18,21 +19,22 @@
 @HiltViewModel
 public class QuizViewModel extends ViewModel {
 
-    private final List<QuizQuestion> questions;
+    private final MutableLiveData<List<QuizQuestion>> questions = new MutableLiveData<>(Collections.emptyList());
     private final MutableLiveData<Integer> currentIndex = new MutableLiveData<>(0);
     private final MutableLiveData<Integer> score = new MutableLiveData<>(0);
     private final LoadQuizQuestionsUseCase loadQuizQuestionsUseCase;
 
     @Inject
     public QuizViewModel(LoadQuizQuestionsUseCase loadQuizQuestionsUseCase) {
         this.loadQuizQuestionsUseCase = loadQuizQuestionsUseCase;
-        questions = loadQuizQuestionsUseCase.invoke();
+        loadQuizQuestionsUseCase.invoke(result -> questions.postValue(result));
     }
 
     public QuizQuestion getCurrentQuestion() {
-        if (questions.isEmpty()) return null;
+        List<QuizQuestion> list = questions.getValue();
+        if (list == null || list.isEmpty()) return null;
         int index = currentIndex.getValue();
-        return questions.get(Math.min(index, questions.size() - 1));
+        return list.get(Math.min(index, list.size() - 1));
     }
 
     public LiveData<Integer> getCurrentIndex() {
@@ -43,6 +45,10 @@ public LiveData<Integer> getScore() {
         return score;
     }
 
+    public LiveData<List<QuizQuestion>> getQuestions() {
+        return questions;
+    }
+
     public void answer(int optionIndex) {
         QuizQuestion question = getCurrentQuestion();
         if (question != null && optionIndex == question.answerIndex()) {
@@ -52,6 +58,7 @@ public void answer(int optionIndex) {
     }
 
     public int getTotalQuestions() {
-        return questions.size();
+        List<QuizQuestion> list = questions.getValue();
+        return list != null ? list.size() : 0;
     }
 }

app/src/test/java/com/d4rk/androidtutorials/java/data/repository/DefaultQuizRepositoryTest.java

@@ -6,6 +6,8 @@
 import org.junit.Test;
 
 import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 
 import static org.junit.Assert.*;
 
@@ -19,18 +21,23 @@ private static class FakeQuizLocalDataSource implements QuizLocalDataSource {
         }
 
         @Override
-        public List<QuizQuestion> loadQuestions() {
-            return questions;
+        public void loadQuestions(QuestionsCallback callback) {
+            callback.onResult(questions);
         }
     }
 
     @Test
-    public void loadQuestionsReturnsLocalData() {
+    public void loadQuestionsReturnsLocalData() throws InterruptedException {
         List<QuizQuestion> expected = List.of(
                 new QuizQuestion("Q", new String[]{"A", "B"}, 0)
         );
         FakeQuizLocalDataSource local = new FakeQuizLocalDataSource(expected);
         DefaultQuizRepository repository = new DefaultQuizRepository(local);
-        assertEquals(expected, repository.loadQuestions());
+        CountDownLatch latch = new CountDownLatch(1);
+        repository.loadQuestions(result -> {
+            assertEquals(expected, result);
+            latch.countDown();
+        });
+        assertTrue(latch.await(1, TimeUnit.SECONDS));
     }
 }