Develop Reference

Android: unable to zip generated files

I'm working on this project where I generated CSV files from contact list, and now I'm supposed to package all the files as a single zip archive using RxJava, so I'm trying to get the method to create an archive invoked using onComplete method. But the application is crashing with this error:
Attempt to invoke direct method 'boolean appjoe.wordpress.com.testdemo.Tab2$FileHelper.zip(java.lang.String, java.lang.String)' on a null object reference
This is my code:
path: /storage/emulated/0/Android/data/com.wordpress.appjoe/csv
File location = new File(Environment.getExternalStorageDirectory(), "Android/data/com.wordpress.appjoe/csv/");
File fileLocation;
FileOutputStream dest;
String path;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_tab2, container, false);
mbutton = v.findViewById(R.id.extractContact);
mbutton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
// Permission has already been granted
Observer observer = new Observer() {
#Override
public void onSubscribe(Disposable d) {
mCursor = getCursor();
fCursor = getCursor();
location.mkdirs();
path = location.getAbsolutePath();
try {
dest = new FileOutputStream(path);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
#Override
public void onNext(Object o) {
contactData = o.toString();
fCursor.moveToPosition(count);
fileLocation = new File(path, getName(fCursor)+".csv");
try {
FileOutputStream fileOut = new FileOutputStream(fileLocation);
fileOut.write(contactData.getBytes());
fileOut.flush();
fileOut.close();
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void onError(Throwable e) {
}
#Override
public void onComplete() {
mCursor.close();
fCursor.close();
// Creating archive once the CSV files are generated
if (fileHelper.zip(path, location.getParent())) {
Toast.makeText(getContext(), "Zip successful", Toast.LENGTH_SHORT).show();
}
Log.d("fileLocation", "location: " + location.getParent());
Log.d("fileLocation", "path: " + path);
Log.d("Observer_contact", "Completed");
}
};
io.reactivex.Observable.create(new ObservableOnSubscribe<String>() {
#Override
public void subscribe(ObservableEmitter<String> emitter) throws Exception {
try {
for (count = 0; count < mCursor.getCount(); count++) {
emitter.onNext(loadContacts(count));
}
emitter.onComplete();
} catch (Exception e) {
emitter.onError(e);
}
}
}).subscribeOn(Schedulers.io())
.distinct()
.subscribeWith(observer);
}
}
});
// Inflate the layout for this fragment
return v;
}
RxJava implementation to fetch contacts:
public String loadContacts(int i) {
StringBuilder mBuilder = new StringBuilder();
ContentResolver mContentResolver = getActivity().getContentResolver();
mCursor.moveToPosition(i);
if (mCursor.getCount() > 0 ) {
String id = getID(mCursor);
String name = getName(mCursor);
int hasPhoneNumber = hasNumber(mCursor);
if (hasPhoneNumber > 0) {
mBuilder.append("\"").append(name).append("\"");
Cursor cursor = mContentResolver.query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
null,
ContactsContract.CommonDataKinds.Phone.CONTACT_ID + "= ?",
new String[]{id}, null);
assert cursor != null;
while (cursor.moveToNext()) {
String phoneNumber = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER))
.replaceAll("\\s", "");
// if number is not existing in the list, then add number to the string
if (!(mBuilder.toString().contains(phoneNumber))) {
mBuilder.append(", ").append(phoneNumber);
}
}
cursor.close();
}
}
return mBuilder.toString();
}
Methods to get necessary information:
private Cursor getCursor() {
ContentResolver mContentResolver = getActivity().getContentResolver();
return mContentResolver.query(ContactsContract.Contacts.CONTENT_URI,
null, null, null, ContactsContract.Contacts.DISPLAY_NAME + " ASC");
}
private String getID(Cursor cursor) {
String id = cursor.getString(cursor.getColumnIndex(ContactsContract.Contacts._ID));
return id;
}
private String getName(Cursor cursor) {
String name = cursor.getString(cursor.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME));
return name;
}
private int hasNumber(Cursor cursor) {
return Integer.parseInt(cursor.getString(cursor.getColumnIndex(ContactsContract.Contacts.HAS_PHONE_NUMBER)));
}
Class to generate archive
// Custom class to help with zipping of generated CSVs
private class FileHelper {
private static final int BUFFER_SIZE = 2048;
private String TAG = FileHelper.class.getName();
private String parentPath = "";
private String destinationFileName = "Contacts_CSV.zip";
private boolean zip (String sourcePath, String destinationPath) {
new File(destinationPath).mkdirs();
FileOutputStream fileOutputStream;
ZipOutputStream zipOutputStream = null;
try {
if (!destinationPath.endsWith("/")) {
destinationPath = destinationPath + "/";
}
String destination = destinationPath + destinationFileName;
File file = new File(destination);
if (!file.exists()) {
file.createNewFile();
}
fileOutputStream = new FileOutputStream(file);
zipOutputStream = new ZipOutputStream(new BufferedOutputStream(fileOutputStream));
parentPath = new File(sourcePath).getParent() + "/";
zipFile(zipOutputStream, sourcePath);
} catch (IOException e) {
e.printStackTrace();
Log.d(TAG,e.getMessage());
return false;
} finally {
if (zipOutputStream!=null)
try {
zipOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return true;
}
private void zipFile (ZipOutputStream zipOutputStream, String sourcePath) throws IOException {
java.io.File files = new java.io.File(sourcePath);
java.io.File[] fileList = files.listFiles();
String entryPath="";
BufferedInputStream input;
for (java.io.File file : fileList) {
if (file.isDirectory()) {
} else {
byte data[] = new byte[BUFFER_SIZE];
FileInputStream fileInputStream = new FileInputStream(file.getPath());
input = new BufferedInputStream(fileInputStream, BUFFER_SIZE);
entryPath = file.getAbsolutePath().replace(parentPath, "");
ZipEntry entry = new ZipEntry(entryPath);
zipOutputStream.putNextEntry(entry);
int count;
while ((count = input.read(data, 0, BUFFER_SIZE)) != -1) {
zipOutputStream.write(data, 0, count);
}
input.close();
}
}
}
}

I solved this problem by removing the class FileHelper and making both the methods inside FileHelper private methods within the main class. That way, calling the methods from onComplete() didn't cause the program to crash, and it was successfully generating the zip file.

How to read a CSV file?

I am creating an application where i do some real-time image analysis and store them into a csv file. The csv has 2 columns time and y-value of each frame.
I want to read this file and store the values from 2 columns into to double array. I want this because i want to perform an fast Fourier transformation on the data.
public class MainActivity extends AppCompatActivity implements CameraView.PreviewReadyCallback {
private static Camera camera = null;
private CameraView image = null;
private LineChart bp_graph;
private int img_Y_Avg, img_U_Avg, img_V_Avg;
private long end = 0, begin = 0;
double valueY, valueU, valueV;
Handler handler;
private int readingRemaining = 1200;
private static long time1, time2, timeDifference;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
bp_graph = (LineChart)findViewById(R.id.graph);
graph_features();
//open camera
try {
camera = Camera.open();
handler = new Handler();
final Runnable runnable = new Runnable() {
#Override
public void run() {
camera.stopPreview();
camera.release();
}
};
handler.postDelayed(runnable, 30000);
} catch (Exception e) {
Log.d("ERROR", "Failed to get camera: " + e.getMessage());
}
if (camera != null) {
image = new CameraView(this, camera);
FrameLayout camera_view = (FrameLayout) findViewById(R.id.camera_view);
camera_view.addView(image);
image.setOnPreviewReady(this);
}
}
#Override
protected void onResume(){
super.onResume();
}
#Override
protected void onPause() {
super.onPause();
}
#Override
public void onPreviewFrame(long startTime, int ySum, int uSum, int vSum, long endTime) {
begin = startTime;
img_Y_Avg = ySum;
img_U_Avg = uSum;
img_V_Avg = vSum;
end = endTime;
showResults(begin, img_Y_Avg, img_U_Avg, img_V_Avg, end);
}
private void showResults(long startTime, int ySum, int uSum, int vSum, long endTime){
//set value of Y on the text view
TextView valueOfY = (TextView)findViewById(R.id.valueY);
//valueY = img_Y_Avg;
valueOfY.setText(String.valueOf(img_Y_Avg));
//start time in milliseconds
long StartDurationInMs = TimeUnit.MILLISECONDS.convert(begin, TimeUnit.MILLISECONDS);
ArrayList<Long> startOfTime = new ArrayList<>();
startOfTime.add(StartDurationInMs);
//store value to array list
ArrayList<Integer> yAverage = new ArrayList<>();
yAverage.add(img_Y_Avg);
//convert to readable format
String readableDate = new SimpleDateFormat("MMM dd,yyyy, HH:mm:ss.SSS").format(EndDurationInMs);
Log.d("Date ", readableDate);
Log.d("time ", String.valueOf(String.valueOf(yAverage.size())));
//store when all array are generated
Log.d("time ", String.valueOf(StartDurationInMs));
ArrayList<Long> getValues = new ArrayList<>();
for(int i = 0; i < yAverage.size(); i++) {
getValues.add(startOfTime.get(i));
getValues.add((long)(yAverage.get(i)));
}
//store the yAverage and start time to csv file
storeCsv(yAverage, getValues);
Log.d("MyEntryData", String.valueOf(getValues));
}
public void storeCsv(ArrayList<Integer>yAverage, ArrayList<Long>getValues){
String filename = "temporary.csv";
//File directoryDownload = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/bpReader";
//File logDir = new File (directoryDownload, "bpReader"); //Creates a new folder in DOWNLOAD directory
File logDir = new File(path);
logDir.mkdirs();
File file = new File(logDir, filename);
FileOutputStream outputStream = null;
try {
file.createNewFile();
outputStream = new FileOutputStream(file, true);
//outputStream = openFileOutput(filename, Context.MODE_PRIVATE);
for (int i = 0; i < yAverage.size(); i += 2) {
outputStream.write((getValues.get(i) + ",").getBytes());
outputStream.write((getValues.get(i + 1) + "\n").getBytes());
//outputStream.write((getValues.get(i + 2) + ",").getBytes());
//outputStream.write((getValues.get(i + 3) + "\n").getBytes());
}
outputStream.flush();
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
public void readCsv(){
}
}
This is my MainActivity. What I am doing here is getting the data from CameraView class for each frame with the help of an interface that I created. After that im storing the values into a CSV file called temporary.csv.
Issues
I want to read this csv and store the first column(the time) into one double array and the second column(yAverage) into another double array.
I also want to delete the file once i have all the data stored into the into the double array.
How can I do that?

I would suggest youto use an open source library like OpenCSV to get the datafrom the CSV file. When you have the library implemented it's only a matter of iterating through the x and y columns and assign them to an array. With OpenCSV it would look like that. But i would also suggest you an more object orientec approach if the x and y with the same index coords are related to each other.
String csvFile = "/Users/mkyong/csv/country3.csv";
int length = 100; //If you dont know how many entries the csv file has i would suggest to use ArrayList
double[] xCoords = new double[length];
double[] yCoords = new double[length];
CSVReader reader = null;
try {
reader = new CSVReader(new FileReader(csvFile));
String[] line;
int i = 0;
while ((line = reader.readNext()) != null) {
xCoords[i] = Double.parseDouble(line[0]);
yCoords[i] = Double.parseDouble(line[1]);
}
} catch (IOException e) {
e.printStackTrace();
}

From the answer given by Lucas, I got the direction to my solution
public void readCsv(){
//set the path to the file
String getPath = Environment.getExternalStorageDirectory() + "/bpReader";
String csvFile = "temporary.csv";
String path = getPath+ "/" + csvFile;
//File file = new File(path, csvFile);
int length = 500;
double[] xCoords = new double[length];
double[] yCoords = new double[length];
CSVReader reader = null;
try {
File myFile = new File (path);
reader = new CSVReader(new FileReader(myFile));
String[] line;
int i = 0;
while ((line = reader.readNext()) != null) {
xCoords[i] = Double.parseDouble(line[0]) ;
yCoords[i] = Double.parseDouble(line[1]);
Log.d("read:: ", "Time: "+String.valueOf(xCoords[i])+" Y: "+String.valueOf(yCoords[i]));
}
myFile.delete();
} catch (IOException e) {
e.printStackTrace();
}
}
And then i had to add
// https://mvnrepository.com/artifact/org.apache.commons/commons-lang3
compile group: 'org.apache.commons', name: 'commons-lang3', version: '3.6'
to my gradle,, which can be found at MVN repository

reading excel sheet from assets folder in android

How to read data in excel-sheet in assets folder and retrieve database?
'I have an excel sheet where my different tables of database is written and i want to read the excel sheet so to store it in database and then want to retrieve database
public class ReadFileAssetsActivity extends ActionBarActivity
{
private Button btnReadExcel1;
AssetManager assetManager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
btnReadExcel1 = (Button) findViewById(R.id.btnReadExcel1);
btnReadExcel1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (v.getId() == R.id.btnReadExcel1)
readExcelFileFromAssets();
}
}); {
assetManager = getAssets();
}
}
public void readExcelFileFromAssets() {
try {
// Creating Input Stream
File file = new File( "file:\\assets\\winthrop-mobile-data-test-records.xls");
FileInputStream myInput = new
FileInputStream(file)//
// InputStream myInput;
// myInput = assetManager.open("main table.xlsx");
// Create a POIFSFileSystem object
POIFSFileSystem myFileSystem = new POIFSFileSystem(myInput);
// Create a workbook using the File System
HSSFWorkbook myWorkBook = new HSSFWorkbook(myFileSystem);
// Get the first sheet from workbook
HSSFSheet mySheet = myWorkBook.getSheetAt(0);
/** We now need something to iterate through the cells.
**/
Iterator<Row> rowIter = mySheet.rowIterator();
while (rowIter.hasNext()) {
HSSFRow myRow = (HSSFRow) rowIter.next();
Iterator<Cell> cellIter = myRow.cellIterator();
while (cellIter.hasNext()) {
HSSFCell myCell = (HSSFCell) cellIter.next();
Log.e("FileUtils", "Cell Value: " + myCell.toString()
+ " Index :" + myCell.getColumnIndex());
// Toast.makeText(getApplicationContext(), "cell Value:
" + // myCell.toString(), Toast.LENGTH_SHORT).show();
}
}
} catch (Exception e) {
e.printStackTrace();
}
return;
}'

how to read the file greater then 1mb

i have create an app in which i am reading the files from phone memory it can read any of the file but when i am reading .vcf file.but when it is smaller than 1 mb ,give correct result,if it is greater than 1 mb,it return nothing.how can i read the data from file.please suggest something.
File_Explore
public class File_Explorer extends Activity {
// Stores names of traversed directories
ArrayList<String> str = new ArrayList<String>();
// Check if the first level of the directory structure is the one showing
private Boolean firstLvl = true;
String aDataRow = "";
static StringBuilder aBuffer = new StringBuilder();
String aBuffer1="";
private static final String TAG = "F_PATH";
private Item[] fileList;
private File path = new File(Environment.getExternalStorageDirectory().getAbsolutePath());
private String chosenFile;
private static final int DIALOG_LOAD_FILE = 0;
static String fileExtension="";
ListAdapter adapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
loadFileList();
showDialog(DIALOG_LOAD_FILE);
Log.d(TAG, path.getAbsolutePath());
}
private void loadFileList() {
try {
path.mkdirs();
} catch (SecurityException e) {
Log.e(TAG, "unable to write on the sd card ");
}
// Checks whether path exists
if (path.exists()) {
FilenameFilter filter = new FilenameFilter() {
#Override
public boolean accept(File dir, String filename) {
File sel = new File(dir, filename);
// Filters based on whether the file is hidden or not
return (sel.isFile() || sel.isDirectory())
&& !sel.isHidden();
}
};
String[] fList = path.list(filter);
fileList = new Item[fList.length];
for (int i = 0; i < fList.length; i++) {
fileList[i] = new Item(fList[i], R.drawable.ic_launcher);
// Convert into file path
File sel = new File(path, fList[i]);
// Set drawables
if (sel.isDirectory()) {
fileList[i].icon = R.drawable.ic_launcher;
Log.d("DIRECTORY", fileList[i].file);
} else {
Log.d("FILE", fileList[i].file);
}
}
if (!firstLvl) {
Item temp[] = new Item[fileList.length + 1];
for (int i = 0; i < fileList.length; i++) {
temp[i + 1] = fileList[i];
}
temp[0] = new Item("Back", R.drawable.ic_launcher);
fileList = temp;
}
} else {
Log.e(TAG, "path does not exist");
}
adapter = new ArrayAdapter<Item>(this,
android.R.layout.select_dialog_item, android.R.id.text1,
fileList) {
#Override
public View getView(int position, View convertView, ViewGroup parent) {
// creates view
View view = super.getView(position, convertView, parent);
TextView textView = (TextView) view
.findViewById(android.R.id.text1);
// put the image on the text view
textView.setCompoundDrawablePadding(
fileList[position].icon);
return view;
}
};
}
private class Item {
public String file;
public int icon;
public Item(String file, Integer icon) {
this.file = file;
this.icon = icon;
}
#Override
public String toString() {
return file;
}
}
#Override
protected Dialog onCreateDialog(int id) {
Dialog dialog = null;
AlertDialog.Builder builder = new Builder(this);
if (fileList == null) {
Log.e(TAG, "No files loaded");
dialog = builder.create();
return dialog;
}
switch (id) {
case DIALOG_LOAD_FILE:
builder.setTitle("Choose your file");
builder.setAdapter(adapter, new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
chosenFile = fileList[which].file;
File sel = new File(path + "/" + chosenFile);
if (sel.isDirectory()) {
firstLvl = false;
// Adds chosen directory to list
str.add(chosenFile);
fileList = null;
path = new File(sel + "");
loadFileList();
removeDialog(DIALOG_LOAD_FILE);
showDialog(DIALOG_LOAD_FILE);
Log.d(TAG, path.getAbsolutePath());
}
// Checks if 'up' was clicked
else if (chosenFile.equalsIgnoreCase("Back") && !sel.exists()) {
// present directory removed from list
String s = str.remove(str.size() - 1);
// path modified to exclude present directory
path = new File(path.toString().substring(0,
path.toString().lastIndexOf(s)));
fileList = null;
// if there are no more directories in the list, then
// its the first level
if (str.isEmpty()) {
firstLvl = true;
}
loadFileList();
removeDialog(DIALOG_LOAD_FILE);
showDialog(DIALOG_LOAD_FILE);
Log.d(TAG, path.getAbsolutePath());
}
// File picked
else {
// Perform action with file picked
fileExtension
= MimeTypeMap.getFileExtensionFromUrl(sel.toString());
// Toast.makeText(getApplication(), fileExtension, Toast.LENGTH_LONG).show();
try{
// ArrayList<String> MyFiles = new ArrayList<String>();
FileInputStream fIn = new FileInputStream(sel);
BufferedReader myReader = new BufferedReader(
new InputStreamReader(fIn));
while ((aDataRow = myReader.readLine()) != null) {
aBuffer.append(aDataRow.toString()).append("\n");
}
// aBuffer1 = aBuffer.toString();
myReader.close();
}catch (FileNotFoundException e)
{e.printStackTrace();}
catch (IOException e) {
e.printStackTrace();
}
// Toast.makeText(getApplicationContext(),aBuffer,Toast.LENGTH_LONG).show();
Intent returnIntent = new Intent();
returnIntent.putExtra("name", aBuffer.toString());
setResult(RESULT_OK, returnIntent);
finish();
}
aBuffer.delete(0, aBuffer.length());
// aBuffer1=null;
}
}
);
break;
}
dialog = builder.show();
return dialog;
}
#Override
public void onBackPressed() {
// TODO Auto-generated method stub
super.onBackPressed();
Intent i= new Intent(this, File_Selecter.class);
startActivity(i);
}
}

If you do not need whole 1MB (capital B by the way) read (which is usually the case), then read only the part you need. And if you do not know where the part you need is (so you cannot seek()), read in smaller chunks unless you find what you need to read from the file.

Android program to convert the SQLite database to excel

I want to change the sqlite database .db file to excel.
But I am not able to find what exactly I have to do. Can anybody please elaborate in a simple way what I have to perform to achieve this task.
By searching on Google, so many links appears, but I am not able to understand the step by step way to do this.
I have followed these links:
1. How to convert excel sheet into database of sqlite in android
2. SQlite database programmatically convert into Excel file format in Android
3. http://opencsv.sourceforge.net/

My solution is to convert the sqlite database into csv in first step then in second step is to convert the csv file to xls and it works fine for me, you will need 2 libraries (opencsv-1.7.jar; poi-3.8-20120326.jar)
public class ExportDatabaseCSVTask extends AsyncTask<String, Void, Boolean>
{
private final ProgressDialog dialog = new ProgressDialog(DatabaseExampleActivity.this);
#Override
protected void onPreExecute()
{
this.dialog.setMessage("Exporting database...");
this.dialog.show();
}
protected Boolean doInBackground(final String... args)
{
File dbFile=getDatabasePath("database_name");
//AABDatabaseManager dbhelper = new AABDatabaseManager(getApplicationContext());
AABDatabaseManager dbhelper = new AABDatabaseManager(DatabaseExampleActivity.this) ;
System.out.println(dbFile); // displays the data base path in your logcat
File exportDir = new File(Environment.getExternalStorageDirectory(), "");
if (!exportDir.exists())
{
exportDir.mkdirs();
}
File file = new File(exportDir, "excerDB.csv");
try
{
if (file.createNewFile()){
System.out.println("File is created!");
System.out.println("myfile.csv "+file.getAbsolutePath());
}else{
System.out.println("File already exists.");
}
CSVWriter csvWrite = new CSVWriter(new FileWriter(file));
//SQLiteDatabase db = dbhelper.getWritableDatabase();
Cursor curCSV=db.getdb().rawQuery("select * from " + db.TABLE_NAME,null);
csvWrite.writeNext(curCSV.getColumnNames());
while(curCSV.moveToNext())
{
String arrStr[] ={curCSV.getString(0),curCSV.getString(1),curCSV.getString(2)};
/*curCSV.getString(3),curCSV.getString(4)};*/
csvWrite.writeNext(arrStr);
}
csvWrite.close();
curCSV.close();
/*String data="";
data=readSavedData();
data= data.replace(",", ";");
writeData(data);*/
return true;
}
catch(SQLException sqlEx)
{
Log.e("MainActivity", sqlEx.getMessage(), sqlEx);
return false;
}
catch (IOException e)
{
Log.e("MainActivity", e.getMessage(), e);
return false;
}
}
protected void onPostExecute(final Boolean success)
{
if (this.dialog.isShowing())
{
this.dialog.dismiss();
}
if (success)
{
Toast.makeText(DatabaseExampleActivity.this, "Export succeed", Toast.LENGTH_SHORT).show();
}
else
{
Toast.makeText(DatabaseExampleActivity.this, "Export failed", Toast.LENGTH_SHORT).show();
}
}}
Export CSV to XLS part
public class CSVToExcelConverter extends AsyncTask<String, Void, Boolean> {
private final ProgressDialog dialog = new ProgressDialog(DatabaseExampleActivity.this);
#Override
protected void onPreExecute()
{this.dialog.setMessage("Exporting to excel...");
this.dialog.show();}
#Override
protected Boolean doInBackground(String... params) {
ArrayList arList=null;
ArrayList al=null;
//File dbFile= new File(getDatabasePath("database_name").toString());
File dbFile=getDatabasePath("database_name");
String yes= dbFile.getAbsolutePath();
String inFilePath = Environment.getExternalStorageDirectory().toString()+"/excerDB.csv";
outFilePath = Environment.getExternalStorageDirectory().toString()+"/test.xls";
String thisLine;
int count=0;
try {
FileInputStream fis = new FileInputStream(inFilePath);
DataInputStream myInput = new DataInputStream(fis);
int i=0;
arList = new ArrayList();
while ((thisLine = myInput.readLine()) != null)
{
al = new ArrayList();
String strar[] = thisLine.split(",");
for(int j=0;j<strar.length;j++)
{
al.add(strar[j]);
}
arList.add(al);
System.out.println();
i++;
}} catch (Exception e) {
System.out.println("shit");
}
try
{
HSSFWorkbook hwb = new HSSFWorkbook();
HSSFSheet sheet = hwb.createSheet("new sheet");
for(int k=0;k<arList.size();k++)
{
ArrayList ardata = (ArrayList)arList.get(k);
HSSFRow row = sheet.createRow((short) 0+k);
for(int p=0;p<ardata.size();p++)
{
HSSFCell cell = row.createCell((short) p);
String data = ardata.get(p).toString();
if(data.startsWith("=")){
cell.setCellType(Cell.CELL_TYPE_STRING);
data=data.replaceAll("\"", "");
data=data.replaceAll("=", "");
cell.setCellValue(data);
}else if(data.startsWith("\"")){
data=data.replaceAll("\"", "");
cell.setCellType(Cell.CELL_TYPE_STRING);
cell.setCellValue(data);
}else{
data=data.replaceAll("\"", "");
cell.setCellType(Cell.CELL_TYPE_NUMERIC);
cell.setCellValue(data);
}
//*/
// cell.setCellValue(ardata.get(p).toString());
}
System.out.println();
}
FileOutputStream fileOut = new FileOutputStream(outFilePath);
hwb.write(fileOut);
fileOut.close();
System.out.println("Your excel file has been generated");
} catch ( Exception ex ) {
ex.printStackTrace();
} //main method ends
return true;
}
protected void onPostExecute(final Boolean success)
{
if (this.dialog.isShowing())
{
this.dialog.dismiss();
}
if (success)
{
Toast.makeText(DatabaseExampleActivity.this, "file is built!", Toast.LENGTH_LONG).show();
}
else
{
Toast.makeText(DatabaseExampleActivity.this, "file fail to build", Toast.LENGTH_SHORT).show();
}
}
}

I know this question is a little old but it provided me with the answer to the same question. I've cleaned up the code a little and done away with the need to write a csv file altogether by getting my database helper class to return me an ArrayList. Still using Apache POI though.
File folder =new File(Environment.getExternalStorageDirectory()+APP_FILES_PATH);
if(!folder.exists())
{
folder.mkdir();
}
DatabaseHelper dbHelper = DatabaseHelper.getInstance(context);
ArrayList<String[]> exts = dbHelper.getExtinguisherArray(1);
HSSFWorkbook hwb = new HSSFWorkbook();
HSSFSheet sheet = hwb.createSheet("extinguishers");
for(int x = 0; x < exts.size(); x++)
{
String[] arr = exts.get(x);
HSSFRow row = sheet.createRow(x);
for(int i = 0; i< arr.length; i++)
{
HSSFCell cell = row.createCell(i);
String data = arr[i];
cell.setCellValue(data);
}
}
FileOutputStream fileOut = new FileOutputStream(Environment.getExternalStorageDirectory()+APP_FILES_PATH+"file.xls");
hwb.write(fileOut);
fileOut.close();

Export Android SqliteDb to CSV format
You need to do these step...
add this jar file opencsv-1.7.jar http://www.java2s.com/Code/Jar/o/Downloadopencsv17jar.htm
And then use this code
public class ExportDatabaseToCSV{
Context context;
public ExportDatabaseToCSV(Context context) {
this.context=context;
}
public void exportDataBaseIntoCSV(){
CredentialDb db = new CredentialDb(context);//here CredentialDb is my database. you can create your db object.
File exportDir = new File(Environment.getExternalStorageDirectory(), "");
if (!exportDir.exists())
{
exportDir.mkdirs();
}
File file = new File(exportDir, "csvfilename.csv");
try
{
file.createNewFile();
CSVWriter csvWrite = new CSVWriter(new FileWriter(file));
SQLiteDatabase sql_db = db.getReadableDatabase();//here create a method ,and return SQLiteDatabaseObject.getReadableDatabase();
Cursor curCSV = sql_db.rawQuery("SELECT * FROM "+CredentialDb.TABLE_NAME,null);
csvWrite.writeNext(curCSV.getColumnNames());
while(curCSV.moveToNext())
{
//Which column you want to export you can add over here...
String arrStr[] ={curCSV.getString(0),curCSV.getString(1), curCSV.getString(2)};
csvWrite.writeNext(arrStr);
}
csvWrite.close();
curCSV.close();
}
catch(Exception sqlEx)
{
Log.e("Error:", sqlEx.getMessage(), sqlEx);
}
}
}

In addition to #user2324120's answer, and as we're in Android, you can directly add the libs to gradle (and therefore you don't need to download the jars) :
compile 'com.opencsv:opencsv:3.7'
compile 'org.apache.poi:poi:3.14'
I also did it a different way, a way more customisable one (and without useless CSV transition). Here it is, with a few comments :
public static Pair<Boolean, String> exportToXLS(Context context, boolean byAuthor) {
try {
HSSFWorkbook workbook = new HSSFWorkbook();
HSSFSheet sheet = workbook.createSheet(context.getString(R.string.sheet_name)); // Good for localization
initSheetColumns(context, workbook, sheet, byAuthor);
addBooksToSheet(sheet, byAuthor);
setColumsWidth(sheet);
OutputStream outputStream = new FileOutputStream(new File(Methods.getDownloadsDirectory(), byAuthor ? context.getString(R.string.mylibrary_by_author_xls) : context.getString(R.string.mylibrary_xls)).getAbsolutePath());
workbook.write(outputStream);
outputStream.flush();
outputStream.close();
return new Pair<>(true, context.getString(R.string.database_saved));
} catch (Exception e) {
e.printStackTrace();
return new Pair<>(false, context.getString(R.string.an_error_has_occured_during_xls_file_creation));
}
}
private static void initSheetColumns(Context context, HSSFWorkbook workbook, HSSFSheet sheet, boolean byAuthor) {
HSSFRow row = sheet.createRow(0);
HSSFCell cell = row.createCell(0);
cell.setCellValue(byAuthor ? context.getString(R.string.db_author) : context.getString(R.string.db_title));
cell = row.createCell(1);
cell.setCellValue(byAuthor ? context.getString(R.string.db_title) : context.getString(R.string.db_author));
cell = row.createCell(2);
cell.setCellValue(context.getString(R.string.db_publisheddate));
/*
etc.
*/
boldHeaders(workbook, row);
}
private static void boldHeaders(HSSFWorkbook workbook, HSSFRow row) {
HSSFCellStyle style = workbook.createCellStyle();
/* Do your own style
...
*/
for (int i = 0; i < 8; i++) {
row.getCell(i).setCellStyle(style);
}
}
// Allow data personalisation and localisation if needed
private static void addBooksToSheet(HSSFSheet sheet, boolean byAuthor) {
int i = 1;
List<Book> books = Book.listAll(Book.class); // I use Sugar library here, if you're not just make a simple db query to get your objects
Collections.sort(books, byAuthor ? Book.bookAuthorComparator : Book.bookNameComparator);
for (Book book : books) {
HSSFRow row = sheet.createRow(i);
HSSFCell cell = row.createCell(0);
cell.setCellValue(byAuthor ? getBookValue(book, true) : book.getTitle());
cell = row.createCell(1);
cell.setCellValue(byAuthor ? book.getTitle() : getBookValue(book, false));
cell = row.createCell(2);
cell.setCellValue(book.getPublishedDate());
/*
etc.
*/
i++;
}
}
private static void setColumsWidth(HSSFSheet sheet) {
for (int i = 0; i < 8; i++) {
sheet.setColumnWidth(i, 255 * getMaxNumCharacters(sheet, i)); // Autosize not working on Android
}
}
// My method to get the max num char, if it can hekp
public static int getMaxNumCharacters(Sheet sheet, int column) {
int max = 0;
for (int rowIndex = 0; rowIndex <= sheet.getLastRowNum(); rowIndex++) {
Row row = sheet.getRow(rowIndex);
if (row == null) {
continue;
}
Cell cell = row.getCell(column);
if (cell != null) {
int nb = cell.getStringCellValue().length();
if (nb > max) {
max = nb;
}
}
}
max = (int) (max * 1.1);
if (max > 255) {
return 255; // max 255 char for width
}
return max;
}
Hope it helps!