Backup database to external storage

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.java2s.myapplication3.app" >
    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />
    <uses-permission android:name="com.java2s.myapplication3.app.READ_PREFERENCES" />
    <uses-permission android:name="com.java2s.myapplication3.app.WRITE_PREFERENCES" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="java2s.com"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.java2s.myapplication3.app.MainActivity"
            android:label="java2s.com"
            >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
</LinearLayout>

package com.java2s.myapplication3.app;
/*  ww  w .  ja va2  s .  com*/

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

import android.content.Context;
import android.os.AsyncTask;
import android.os.Environment;
import android.app.Activity;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.os.Environment;
import android.widget.Toast;

public class MainActivity extends Activity implements BackupTask.CompletionListener {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        SQLiteDatabase db = openOrCreateDatabase("mydb", Activity.MODE_PRIVATE, null);
        db.close();
    }

    @Override
    public void onResume() {
        super.onResume();
        if( Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) ) {
            BackupTask task = new BackupTask(this);
            task.setCompletionListener(this);
            task.execute(BackupTask.COMMAND_RESTORE);
        }
    }

    @Override
    public void onPause() {
        super.onPause();
        if( Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) ) {
            BackupTask task = new BackupTask(this);
            task.execute(BackupTask.COMMAND_BACKUP);
        }
    }

    @Override
    public void onBackupComplete() {
        Toast.makeText(this, "Backup Successful", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onError(int errorCode) {
        if(errorCode == BackupTask.RESTORE_NOFILEERROR) {
            Toast.makeText(this, "No Backup Found to Restore", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "Error During Operation: "+errorCode, Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onRestoreComplete() {
        Toast.makeText(this, "Restore Successful", Toast.LENGTH_SHORT).show();
    }
}
class BackupTask extends AsyncTask<String,Void,Integer> {
    public interface CompletionListener {
        void onBackupComplete();
        void onRestoreComplete();
        void onError(int errorCode);
    }

    public static final int BACKUP_SUCCESS = 1;
    public static final int RESTORE_SUCCESS = 2;
    public static final int BACKUP_ERROR = 3;
    public static final int RESTORE_NOFILEERROR = 4;

    public static final String COMMAND_BACKUP = "backupDatabase";
    public static final String COMMAND_RESTORE = "restoreDatabase";

    private Context mContext;
    private CompletionListener listener;

    public BackupTask(Context context) {
        super();
        mContext = context;
    }

    public void setCompletionListener(CompletionListener aListener) {
        listener = aListener;
    }

    @Override
    protected Integer doInBackground(String... params) {
        File dbFile = mContext.getDatabasePath("mydb");
        File exportDir = new File(Environment.getExternalStorageDirectory(), "myAppBackups");
        if (!exportDir.exists()) {
            exportDir.mkdirs();
        }
        File backup = new File(exportDir, dbFile.getName());
        String command = params[0];
        if(command.equals(COMMAND_BACKUP)) {
            //Attempt file copy
            try {
                backup.createNewFile();
                fileCopy(dbFile, backup);
                return BACKUP_SUCCESS;
            } catch (IOException e) {
                return BACKUP_ERROR;
            }
        } else if(command.equals(COMMAND_RESTORE)) {
            //Attempt file copy
            try {
                if(!backup.exists()) {
                    return RESTORE_NOFILEERROR;
                }
                dbFile.createNewFile();
                fileCopy(backup, dbFile);
                return RESTORE_SUCCESS;
            } catch (IOException e) {
                return BACKUP_ERROR;
            }
        } else {
            return BACKUP_ERROR;
        }
    }

    @Override
    protected void onPostExecute(Integer result) {

        switch(result) {
            case BACKUP_SUCCESS:
                if(listener != null) {
                    listener.onBackupComplete();
                }
                break;
            case RESTORE_SUCCESS:
                if(listener != null) {
                    listener.onRestoreComplete();
                }
                break;
            case RESTORE_NOFILEERROR:
                if(listener != null) {
                    listener.onError(RESTORE_NOFILEERROR);
                }
                break;
            default:
                if(listener != null) {
                    listener.onError(BACKUP_ERROR);
                }
        }
    }

    private void fileCopy(File source, File dest) throws IOException {
        FileChannel inChannel = new FileInputStream(source).getChannel();
        FileChannel outChannel = new FileOutputStream(dest).getChannel();
        try {
            inChannel.transferTo(0, inChannel.size(), outChannel);
        } finally {
            if (inChannel != null)
                inChannel.close();
            if (outChannel != null)
                outChannel.close();
        }
    }
}