How to export Android Room Database to Json

In this android programming source code example, we are going to export Android Room Database to Json.

You can copy and adopt this source code example to your android project without reinventing the wheel.

Below is a step by step source code to export Android Room Database to Json.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="15dp">

    <TextView
        android:id="@+id/genjson"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <Button
        android:id="@+id/genBtn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorAccent"
        android:layout_below="@id/genjson"
        android:textColor="#ffffff"
        android:text="Generate"/>

</RelativeLayout>

MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

import java.lang.reflect.Type;
import java.util.List;

import io.reactivex.Completable;
import io.reactivex.CompletableObserver;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.disposables.Disposable;
import io.reactivex.functions.Action;
import io.reactivex.schedulers.Schedulers;

public class RoomDatabaseActivity5 extends AppCompatActivity {
    private TextView jsontxt;
    private Button genjson;
    private UserDatabase userDatabase;
    private List<User> responseList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_room_database5);
        jsontxt = (TextView) findViewById(R.id.genjson);
        genjson = (Button) findViewById(R.id.genBtn);
        userDatabase = UserDatabase.getInstance(this);
        genjson.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                generateData();
            }
        });
    }

    private void generateData(){
        Completable.fromAction(new Action() {
            @Override
            public void run() throws Exception {
                userDatabase.userDAO().getuserList();
            }
        }).observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .subscribe(new CompletableObserver() {
                    @Override
                    public void onSubscribe(Disposable d) {
                    }

                    @Override
                    public void onComplete() {
                        responseList = userDatabase.userDAO().getuserList();
                        Gson gson = new Gson();
                        Type type = new TypeToken<List<User>>(){}.getType();
                        String json = gson.toJson(responseList, type);
                        jsontxt.setText(json);
                    }

                    @Override
                    public void onError(Throwable e) {
                        Toast.makeText(RoomDatabaseActivity5.this, "Empty data",Toast.LENGTH_LONG).show();
                    }
                });
    }
}

UserDatabase.java

import android.arch.persistence.db.SupportSQLiteDatabase;
import android.arch.persistence.room.Database;
import android.arch.persistence.room.Room;
import android.arch.persistence.room.RoomDatabase;
import android.content.Context;
import android.support.annotation.NonNull;

import java.util.concurrent.Executors;

@Database(entities = { User.class }, version = 1, exportSchema = false)
public abstract class UserDatabase extends RoomDatabase {
    private static final String DB_NAME ="UserDb";
    private static UserDatabase instance;
    public abstract UserDAO userDAO();    

    public synchronized static UserDatabase getInstance(final Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context, UserDatabase.class, DB_NAME)
                                        .allowMainThreadQueries().build();
        }
        return instance;
    }
}

User.java

import android.arch.persistence.room.ColumnInfo;
import android.arch.persistence.room.Entity;
import android.arch.persistence.room.Ignore;
import android.arch.persistence.room.PrimaryKey;

@Entity(tableName = "users")
public class User {
    @PrimaryKey(autoGenerate = true)
    private int id;
    @ColumnInfo(name = "name")
    private String name;
    public User(int id, String name){
        this.id = id;
        this.name = name;
    }
    @Ignore
    public User(String name){
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public String getName() {
        return name;
    }
}

UserDAO.java

import android.arch.persistence.room.Dao;
import android.arch.persistence.room.Delete;
import android.arch.persistence.room.Insert;
import android.arch.persistence.room.Query;
import android.arch.persistence.room.Update;
import java.util.ArrayList;
import java.util.List;

@Dao
public interface UserDAO {
    @Query("select * from users")
    List<User> getuserList();

    @Insert
    public void insert(User user);

    @Update
    public void update(User user);

    @Delete
    public void delete(User user);

}

build.gradle

implementation 'io.reactivex.rxjava2:rxjava:2.1.9'
implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'
implementation 'android.arch.persistence.room:runtime:1.0.0' 
annotationProcessor 'android.arch.persistence.room:compiler:1.0.0'

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