Copy database from assets folder

Question

I am creating a Dictionary application which uses an existing sqlite database. I have placed my database in assets folder and I am using the following code to copy the database when the app is started for first time. (I have borrowed the idea from this post)

DatabaseHelper.java

public class DatabaseHelper {

private static String DB_PATH = "";
private static String DB_NAME = "abc.sqlite";
private SQLiteDatabase myDatabase;
private Context myContext;

public DatabaseHelper(Context context) {

    myContext = context;

    if (android.os.Build.VERSION.SDK_INT >= 17)
        DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
    else
        DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
    Log.d("path", DB_PATH);
}

public void copyDatabase() {

        InputStream myInput;
        OutputStream outStream;
        try {
            myInput = myContext.getAssets().open(DB_NAME);
            String file = DB_PATH + DB_NAME;
            outStream = new FileOutputStream(file);

            byte[] buffer = new byte[1024];
            int length = 0;
            while ((length = myInput.read(buffer)) >= 0) {
                outStream.write(buffer, 0, length);             
            }
            outStream.flush();
            myInput.close();
            outStream.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

And then I call the above copyDatabase() method form my MainActivity. Here is the code.

public class MainActivity extends Activity {
    DatabaseHelper myDbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.layout);
        myDbHelper = new DatabaseHelper(getApplicationContext());
        myDbHelper.copyDatabase();


    }

}

But the problem is that Android does not copy the database. I have used Log tool, and I found out that the while loop never runs. What's the problem in this code. Thanks.

Answer 1

Change your while loop as below:

Besides your condition >= greater than or equal to change it to only > Greater than

while ((length = myInput.read(buffer)) > 0) {
            outStream.write(buffer, 0, length);             
        }

Try out the below code which will work for you like charm.

public class DataBaseHelper extends SQLiteOpenHelper {
    private Context mycontext;
    private String DB_PATH; 

    private static String DB_NAME = "abc.sqlite";
    public SQLiteDatabase myDataBase;


    public DataBaseHelper(Context context) throws IOException {
        super(context,DB_NAME,null,1);
        this.mycontext=context;
        boolean dbexist = checkdatabase();
        if (dbexist) {
              opendatabase(); 
        } else {
            System.out.println("Database doesn't exist");
            createdatabase();
        }
    }

    public void createdatabase() throws IOException {
        boolean dbexist = checkdatabase();
        if(!dbexist) {
            this.getReadableDatabase();
            try {
                copydatabase();
            } catch(IOException e) {
                throw new Error("Error copying database");
            }
        }
    }   

    private boolean checkdatabase() {

        boolean checkdb = false;
        try {
            String myPath = DB_PATH + DB_NAME;
            File dbfile = new File(myPath);
            checkdb = dbfile.exists();
        } catch(SQLiteException e) {
            System.out.println("Database doesn't exist");
        }
        return checkdb;
    }

    private void copydatabase() throws IOException {
        //Open your local db as the input stream
        InputStream myinput = mycontext.getAssets().open(DB_NAME);

        // Path to the just created empty db
        String outfilename = DB_PATH + DB_NAME;

        //Open the empty db as the output stream
        OutputStream myoutput = new FileOutputStream(outfilename);

        // transfer byte to inputfile to outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myinput.read(buffer))>0) {
            myoutput.write(buffer,0,length);
        }

        //Close the streams
        myoutput.flush();
        myoutput.close();
        myinput.close();
    }

    public void opendatabase() throws SQLException {
        //Open the database
        String mypath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(mypath, null, SQLiteDatabase.OPEN_READWRITE);
    }

    public synchronized void close() {
        if(myDataBase != null) {
            myDataBase.close();
        }
        super.close();
    }

}

In your MainActivity you just now need to create and instance of your DatabaseHelper class others will managed on it own.

public class MainActivity extends Activity {
    DatabaseHelper myDbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.layout);
        myDbHelper = new DatabaseHelper(MainActivity.this);
      }

}