# Java Examples

Here we discuss about an Android todo application using Nitrite database. It uses nitrite as a file based storage engine. It demonstrates the use of Nitrite database in an Android application. The full source code is available here. This tutorial assumes that you have basic knowledge of Android development.

# Setup

To use Nitrite in your Android application, you need to add the following dependency in your app's build.gradle file.

dependencies {
    implementation platform('org.dizitart:nitrite-bom:[latest-version]')
    implementation 'org.dizitart:nitrite'
    implementation 'org.dizitart:nitrite-mvstore-adapter'
}

Also add these pro-guard rules in your proguard-rules.pro file.

proguard
-keep class org.dizitart.no2.** { *; }
-keep class org.slf4j.** { *; }
-keep class org.h2.** { *; }
-keep class org.objenesis.** { *; }
-keep class com.fasterxml.jackson.** { *; }

-keepnames class * implements java.io.Serializable

-keepclassmembers class * implements java.io.Serializable {
    static final long serialVersionUID;
    private static final java.io.ObjectStreamField[] serialPersistentFields;
    !static !transient <fields>;
    private void writeObject(java.io.ObjectOutputStream);
    private void readObject(java.io.ObjectInputStream);
    java.lang.Object writeReplace();
    java.lang.Object readResolve();
}

# Entity Classes

Define a simple Todo entity class to hold your todo data:

import org.dizitart.no2.collection.Document;
import org.dizitart.no2.common.mapper.EntityConverter;
import org.dizitart.no2.common.mapper.NitriteMapper;
import org.dizitart.no2.repository.annotations.Entity;

@Entity
public class TodoItem {
    @Id
    private Integer id;
    private String taskName;
    private Boolean status;
    private String color;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getTaskName() {
        return taskName;
    }

    public void setTaskName(String taskName) {
        this.taskName = taskName;
    }

    public Boolean getStatus() {
        return status;
    }

    public void setStatus(Boolean status) {
        this.status = status;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public static class Converter implements EntityConverter<TodoItem> {

        @Override
        public Class<TodoItem> getEntityType() {
            return TodoItem.class;
        }

        @Override
        public Document toDocument(TodoItem entity, NitriteMapper nitriteMapper) {
            return Document.createDocument()
                    .put("id", entity.getId())
                    .put("taskName", entity.getTaskName())
                    .put("status", entity.getStatus())
                    .put("color", entity.getColor());
        }

        @Override
        public TodoItem fromDocument(Document document, NitriteMapper nitriteMapper) {
            TodoItem item = new TodoItem();
            item.id = document.get("id", Integer.class);
            item.taskName = document.get("taskName", String.class);
            item.status = document.get("status", Boolean.class);
            item.color = document.get("color", String.class);
            return item;
        }
    }
}

And, a list of TodoItem can be represented as:

public class TodoList {
    private String name;
    private String color;

    public TodoList(String name, String color) {
        this.name = name;
        this.color = color;
    }

    public String getName() {
        return name;
    }

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

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }
}

# Database Initialization

To initialize the database and to maintain a singleton instance of the database, you need to create a singleton class NitriteManager as follows:

public class NitriteManager {
    private static NitriteManager _instance = new NitriteManager();
    private static final String dbName = "task.db";
    private static Nitrite db;

    private NitriteManager() {}

    public static NitriteManager getInstance() {
        return _instance;
    }

    private void openDb(Context context) {
        if (db != null) {
            db.close();
        }

        MVStoreModule storeModule = MVStoreModule.withConfig()
                .filePath(context.getDatabasePath(dbName))
                .build();
        SimpleDocumentMapper documentMapper = new SimpleDocumentMapper();
        documentMapper.registerEntityConverter(new TodoItem.Converter());

        db = Nitrite.builder()
                .loadModule(storeModule)
                .loadModule(() -> setOf(documentMapper))
                .openOrCreate();
    }

    public ObjectRepository<TodoItem> getTodoRepository(Context context, String label) {
        if (db == null) {
            openDb(context);
        }

        return db.getRepository(TodoItem.class, label);
    }
}

Next create a data access layer DataBaseManager for CRUD operations:

public class DataBaseManager {

    private final NitriteManager nitriteManager;
    private final String label;

    public DataBaseManager(String label) {
        this.nitriteManager = NitriteManager.getInstance();
        this.label = label;
    }

    public void addTask(Context context, int id, boolean status, String taskName, String taskColor) {
        TodoItem todoItem = new TodoItem();
        todoItem.setId(id);
        todoItem.setColor(taskColor);
        todoItem.setStatus(status);
        todoItem.setTaskName(taskName);
        nitriteManager.getTodoRepository(context, label).insert(todoItem);
    }

    public void removeTask(Context context, int id) {
        nitriteManager.getTodoRepository(context, label).remove(where("id").eq(id));
    }

    public void updateTask(Context context, Boolean taskStatus, int id, String taskName) {
        Document updateDocument = Document.createDocument()
                .put("status", taskStatus)
                .put("taskName", taskName);
        nitriteManager.getTodoRepository(context, label).update(where("id").eq(id), updateDocument);
    }

    public List<TodoItem> readFromDB(Context context) {
        return nitriteManager.getTodoRepository(context, label).find().toList();
    }

    public int getCurrentBiggestId(Context context) {
        TodoItem item = nitriteManager.getTodoRepository(context, label).find(
                FindOptions.orderBy("id", SortOrder.Descending)).firstOrNull();
        if (item == null) return 0;
        return item.getId();
    }
}

# Activity

Now you need to create two activities, one for the todo list and another for the menu.

# Todo List Activity

public class ToDoListActivity extends AppCompatActivity {

    DataBaseManager manager;
    ListView listView;
    CustomAdapter customAdapter;
    TextView activityTitle;
    EditText addTask;
    int currentBiggerId = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_todo_list);
        //naming the activity
        activityTitle = (TextView) findViewById(R.id.activityTitle);
        activityTitle.setText(getIntent().getStringExtra("listName"));
        //getting list color
        String color = getIntent().getStringExtra("listColor");

        addTask = (EditText) findViewById(R.id.editTextAddTask);

        listView = (ListView) findViewById(R.id.listTodo);
        manager = new DataBaseManager(activityTitle.getText().toString());
        listView.setOnItemLongClickListener((parent, view, position, id) -> {
            Log.e("Item Long Click", "Removing the item");
            manager.removeTask(getApplicationContext(), (customAdapter.todoList.get(position)).getId());
            try {
                printDB(true);
            } catch (ExecutionException | InterruptedException e) {
                e.printStackTrace();
            }
            return false;
        });
        try {
            printDB(true);
        } catch (ExecutionException | InterruptedException e) {
            e.printStackTrace();
        }
    }

    public void addTask(View v) {
        Runnable runnable = () -> {
            currentBiggerId = manager.getCurrentBiggestId(getApplicationContext());
            int randomInt = new Random().nextInt(3);
            String color = "";
            switch (randomInt) {
                case 0:
                    color = "blue";
                    break;
                case 1:
                    color = "green";
                    break;
                case 2:
                    color = "violet";
                    break;
            }
            manager.addTask(getApplicationContext(), new Random().nextInt(), false, addTask.getText().toString(), color);
            try {
                printDB(true);
            } catch (ExecutionException | InterruptedException e) {
                e.printStackTrace();
            }
        };
        runnable.run();
    }

    public void printDB(boolean updateFromDb) throws ExecutionException, InterruptedException {
        if (updateFromDb) {
            customAdapter = new CustomAdapter(manager.readFromDB(getApplicationContext()));
            listView.setAdapter(customAdapter);
        }
        customAdapter.notifyDataSetChanged();
        currentBiggerId = manager.getCurrentBiggestId(getApplicationContext());
        addTask.setText("");
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id == R.id.about) {
            Toast.makeText(this, "Nitrite Database Demo", Toast.LENGTH_LONG).show();
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    protected void onResume() {
        super.onResume();
        try {
            printDB(true);
        } catch (ExecutionException | InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(customAdapter.todoList.size());
    }

    public class CustomAdapter extends BaseAdapter {
        List<TodoItem> todoList;

        CustomAdapter(List<TodoItem> todoList) {
            this.todoList = todoList;
        }

        @Override
        public int getCount() {
            return todoList.size();
        }

        @Override
        public Object getItem(int i) {
            return null;
        }

        @Override
        public long getItemId(int i) {
            return i;
        }

        @Override
        public View getView(final int i, View view, ViewGroup viewGroup) {
            view = getLayoutInflater().inflate(R.layout.task_todo_item, null);

            final TextView title = view.findViewById(R.id.todoName);
            title.setText(todoList.get(i).getTaskName());
            CheckBox button = view.findViewById(R.id.checkButton);
            button.setChecked(todoList.get(i).getStatus());

            //region setting color states
            int[][] states = new int[][]{
                    new int[]{-android.R.attr.state_checked}, //disabled
                    new int[]{android.R.attr.state_checked} //enabled
            };
            @SuppressLint("ResourceType") int[] colorBlue = new int[]{Color.parseColor(getString(R.color.colorBlue)),
                    Color.parseColor(getString(R.color.colorBlue))};
            @SuppressLint("ResourceType") int[] colorGreen = new int[]{Color.parseColor(getString(R.color.colorGreen)),
                    Color.parseColor(getString(R.color.colorGreen))};
            @SuppressLint("ResourceType") int[] colorViolet = new int[]{Color.parseColor(getString(R.color.colorViolet)),
                    Color.parseColor(getString(R.color.colorViolet))};
            //endregion

            //region setting UI colors
            RelativeLayout layout = view.findViewById(R.id.itemBackground);
            String color = todoList.get(i).getColor();
            final int taskId = todoList.get(i).getId();
            final String taskName = todoList.get(i).getTaskName();
            if (color.matches("blue")) {
                layout.setBackground(ContextCompat.getDrawable(getApplicationContext(), R.drawable.list_item_background_blue));
                button.setButtonTintList(new ColorStateList(states, colorBlue));
            } else if (color.matches("green")) {
                layout.setBackground(ContextCompat.getDrawable(getApplicationContext(), R.drawable.list_item_background_green));
                button.setButtonTintList(new ColorStateList(states, colorGreen));
            } else {
                layout.setBackground(ContextCompat.getDrawable(getApplicationContext(), R.drawable.list_item_background_violet));
                button.setButtonTintList(new ColorStateList(states, colorViolet));
            }
            //endregion
            button.setOnCheckedChangeListener((compoundButton, b) -> itemChecked(b, taskId, taskName));

            return view;
        }

        void itemChecked(final boolean taskStatus, final int taskId, final String taskName) {
            Runnable runnable = () -> manager.updateTask(getApplicationContext(), taskStatus, taskId, taskName);
            runnable.run();
        }
    }
}

public class ListMenuActivity extends AppCompatActivity {
    ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_menu);
        listView = (ListView) findViewById(R.id.listMenu);
        ArrayList<TodoList> lists = new ArrayList<>();
        lists.add(new TodoList("Home", "blue"));
        lists.add(new TodoList("Work", "green"));
        lists.add(new TodoList("School", "violet"));
        CustomAdapter customAdapter = new CustomAdapter(lists);
        listView.setAdapter(customAdapter);
    }

    public class CustomAdapter extends BaseAdapter {
        ArrayList<TodoList> lists;

        public CustomAdapter(ArrayList<TodoList> lists) {
            this.lists = lists;
        }

        @Override
        public int getCount() {
            return lists.size();
        }

        @Override
        public Object getItem(int i) {
            return null;
        }

        @Override
        public long getItemId(int i) {
            return i;
        }

        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            view = getLayoutInflater().inflate(R.layout.task_menu_item, null);

            //region setting background color
            RelativeLayout layout = view.findViewById(R.id.itemBackground);
            final String color = lists.get(i).getColor();
            if (color.matches("blue"))
                layout.setBackground(ContextCompat.getDrawable(getApplicationContext(), R.drawable.list_item_background_blue));
            else if (color.matches("green"))
                layout.setBackground(ContextCompat.getDrawable(getApplicationContext(), R.drawable.list_item_background_green));
            else
                layout.setBackground(ContextCompat.getDrawable(getApplicationContext(), R.drawable.list_item_background_violet));
            //endregion

            final TextView title = view.findViewById(R.id.listName);
            title.setText(lists.get(i).getName());
            ImageButton button = view.findViewById(R.id.selectList);
            button.setOnClickListener(view1 -> listSelected(title.getText().toString(), color));

            return view;
        }

        void listSelected(String listName, String listColor) {
            Intent intent = new Intent(getApplicationContext(), ToDoListActivity.class);
            intent.putExtra("listName", listName);
            intent.putExtra("listColor", listColor);
            startActivity(intent);
        }
    }
}