Develop Reference

android file system persistance

Hi Iam having serious issues try to persist some serializable objects to a file on the local android file system. Iam getting a Bad file descriptor error and I think it is to do with my methods for creating the file. the file and checking if the file exists. i create a private file object in the class. Then, on write or read. I check file existance with the following code.
#Override
public boolean fileExists() {
File file = context.getFileStreamPath(filename);
return file.exists();
}
this doesnt instantiate my file object called "objectfile"!! but does check the "filename" exists.
to create the file I call this method if "filename" doesnt exist.
public void createFile()
{
objectfile = new File(context.getFilesDir(), filename);
objectfile.setReadable(true);
objectfile.setWritable(true);
}
Iam not sure if this will give me back my previously created file which would be ideally what I want to do. Is there a way i can just get the old file or create a new one and pass it to "objectfile" variable in the constructor??
Iam also wondering what the best way to do this is??
Or should i just use the mysqlite db? using object file persistance doesn't seem to be working out for me right now and iam working to a deadline. Also this method is mention in the gooogle docs so I thought it would be legit was to do it.
http://developer.android.com/training/basics/data-storage/files.html
here is my method for reading the serializable objects
public synchronized ArrayList<RoomItem> readObjects() {
final ArrayList<RoomItem> readlist = new ArrayList<>();
if(!fileExists())
return readlist;
if(objectfile == null)
createFile();
try {
finputstream = new FileInputStream(objectfile);
instream = new ObjectInputStream(finputstream);
readwritethread = new Thread(new Runnable() {
#Override
public void run() {
try {
final ArrayList<RoomItem> readitems = (ArrayList<RoomItem>) instream.readObject();
instream.close();
finputstream.close();
handler.post(new Runnable() {
#Override
public void run() {
listener.updateList(readitems);
}
});
} catch(IOException e)
{
e.printStackTrace();
}
catch(ClassNotFoundException e)
{
e.printStackTrace();
Log.d("read failed", "file read failed");
}
}
});
}
catch(Exception e)
{
e.printStackTrace();
}
timeOutReadWrite(readwritethread);
readwritethread.start();
try {
readwritethread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
Log.d("read from file", "file read");
return readlist;
if anyone could suggest any improvements id really appreciate it. I use a handler to pass back to my activity and implement a listener interface on my activity thats call the activity when all the obj are read. Thanks again!

1#: Yes, it will return the original file you created.
2#: Depends on the thing you want to store, seems File is more flex from description
hope helpful.

We have used
FileOutputStream fos = context.openFileOutput("file.ser", Context.MODE_PRIVATE);
to write our serialized files.This will carete files in /data/data/app.package.name/files/. In fact, this path is returned by getFilesDir().
And while deserializing, use
//make sure you pass the same file that was passed to openFileOutput()..
FileInputStream fis = context.openFileInput("file.ser");
Also, to avoid confusing between file names you can use name of class that is being serialized.
Ex:
public static <T> void serialize(final Context context, final T objectToSerialize) {
....
....
Strin fileName = objectToSerialize.getClass().getSimpleName();
...
}
Do this and keep the method in util so it can be used for any type of objects (T type) to serialize.

Android media player: streaming audio file from HTTPS Url

I have to stream an audio file from Android media player from an application. Initially the file to be streamed was coming from a Http:// url and for which I was Using code-
public void playSample() {
AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {
#Override
protected void onPreExecute() {
mediaPlayer = new MediaPlayer();
}
#Override
protected Void doInBackground(Void... arg0) {
try {
try {
mediaPlayer.setDataSource("http://an.http.url/");
mediaPlayer.prepare();
mediaPlayer.start();
} catch (IOException e) {
Log.e("AudioFileError", "Could not open file for playback.", e);
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(Void result) {
pd.dismiss();
}
};
task.execute((Void[]) null);
}
This code is working as desired with http based file, but now the URL for Audio file was changed to https:// one(i.e., https://an.https.url/) and the code fails with an exception in
mediaPlayer.prepare();
The exception is
Prepare failed.: status=0x1
Please suggest a solution for it.

Media player in android <4.x supports only HTTP and 4.x n above support for BOTH http and https , so while using https with older API level, please think over it use http instead of https.

After long struggle i found solution,
Add below code before setDataSource().
try {
KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
trustStore.load(null, null);
MySSLSocketFactory sf = new MySSLSocketFactory(trustStore);
sf.setHostnameVerifier(MySSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER);
sf.fixHttpsURLConnection();
HostnameVerifier hostnameVerifier = org.apache.http.conn.ssl.SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER;
HttpsURLConnection.setDefaultHostnameVerifier(hostnameVerifier);
} catch (Exception e) {
e.printStackTrace();
}
#update1
Those who are using this answer, Read this caution from developer.android.com. Caution: Many web sites describe a poor alternative solution which is to install a TrustManager that does nothing. If you do this you might as well not be encrypting your communication, because anyone can attack your users at a public Wi-Fi hotspot by using DNS tricks to send your users' traffic through a proxy of their own that pretends to be your server

downloading multiple file with download manager using jsoup and asynctask, not happening

Here is my code:--
public class grabber extends Activity
{
int counter;
String folderPath;
String[] array;
DownloadManager dm;
private long enqueue;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.data);
Down t = new Down();
t.execute();
}
private class Down extends AsyncTask<String, Void, String>
{
protected String doInBackground(String... params)
{
Log.i("grabber", "in back");
String w =Environment.getExternalStorageDirectory().getAbsoluteFile()+"/Android/data/myfolder";
createdir(w);
String link = "http://mywebsitehere.com";
Document doc;
array = new String[200];
try {
doc = Jsoup.connect(link).get();
String title = doc.title();
folderPath = w+ File.separator+title;
createdir(folderPath);
Elements images = doc.select("img[src~=(?i)\\.(png|jpe?g|gif)]");
counter =0;
for (Element image : images)
{
String img = image.attr("src");
array[counter]=img;
counter++;
}
} catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String result)
{
Toast.makeText(getApplicationContext(),
"done", Toast.LENGTH_SHORT).show();
for(int i=0;i<counter;i++)
{
dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
Request request = new Request(
Uri.parse(array[i]));
request.setDescription("Android Data download using DownloadManager.");
request.setDestinationInExternalFilesDir(getApplicationContext(),folderPath,File.separator+"pic"+Integer.toString(i)+".jpg");
enqueue = dm.enqueue(request);
}
}
}
public void createdir(String Path)
{
File file = new File(Path);
if(!file.exists())
{
file.mkdirs();
}
}
}
What it should do:-
It should download the given links, which contains images, to the given path.
What it does:-
The app is running quite fine, my UI is not hanging. After a few second "done" Toast is shown, which means theasynctask is completed and we are at onPostExecute. But when I check the dir I am seeing that there is no folder inside Android/data/myfolder.
The main setback is that some times it works, i.e. the images are downloaded and sometimes not.
So I am guessing maybe its because of some http timeout or some error which I am not handling correctly because I am using createdir(folderPath); after Jsoup and maybe the error is happening there so no folder is getting created there.
Any Ideas!?? Thanks in Advance.
Edit:-
I am getting SocketTimeoutException during jsoup.connect(link).get();

You have to add the following permission to the manifest of your application, to write to the external storage.
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
I hope you did this?

Finally I did it with some trial and error.
We can use timeout option here to reduce the Sockettimeoutexception by changing
doc = Jsoup.connect(link).get();
to
doc = Jsoup.connect(link).timeout(10000).get();
And there is still one other error, thats to remove the Toast message in the onPostExecute as we cannot interact without handler from background task to UI.
That's it.

Download images with AsyncTask

I'm not really sure what goes wrong with my code or structure. I wanted to use AsyncTask to download images and display out the progress bar at the mean time. But I tried out a few different way of doing it. It still failed and no idea what's wrong with it. My structure flow is
ContentID is a string array that stores the content ID of the Images.
Primary Issue: It managed to download images from the url and store into the phone, but the downloaded images are all the same image. It should be different images, it's not what I expected.
Secondary Issue: The progress bar pop up while the application downloading images, but the progress bar did not update it's progress. It just remains 0% and dismissed after the download completed.
I wanted to know what causes primary and secodary issue as i mentioned. Please leave a comment or answer if you might know what's wrong with my code. Any help will be appreciated.
if(isSyncSuccess){
SetConstant.IMAGE_EXIST = 1;
pDialog = new ProgressDialog(GalleryScreen.this);
pDialog.setMessage("Downloading file. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setProgress(0);
pDialog.setMax(contentId.length);
pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pDialog.setCancelable(true);
if (contentId.length>0){
Log.i(TAG, "contentid.length:" +contentId.length);
for (int i=0;i<contentId.length;i++){
if(helper.databaseChecking(useremail, contentId[i])){
contentdownload = i;
SetConstant.CONTENT_ID = contentId[i];
String URL = SetConstant.URL_DOWNLOAD_CONTENT+contentId[i];
DownloadFile downloadFile = new DownloadFile();
downloadFile.execute(URL);
}
private class DownloadFile extends AsyncTask<String, Integer, String>{
#Override
protected String doInBackground(String... sUrl){
Bitmap bm;
InputStream in;
try{
in = new java.net.URL(sUrl[0]).openStream();
bm = BitmapFactory.decodeStream(new PatchInputStream(in));
File storage = new File(Environment.getExternalStorageDirectory() + File.separator + "/Image/");
Log.i(TAG,"storage:" +storage);
Log.i(TAG,"storage:" +storage.getAbsolutePath());
if(!storage.exists()){
storage.mkdirs();
}
String FileName = "/"+SetConstant.CONTENT_ID+".jpg";
FileOutputStream fos = new FileOutputStream(storage + FileName);
bm.compress(Bitmap.CompressFormat.JPEG, 85, fos);
String filepath = storage + FileName;
File filecheck = new File (filepath);
long fileSize = filecheck.length();
fos.flush();
fos.close();
Log.i(TAG, "bm:" +bm);
Log.i(TAG, "fos:" +fos);
Log.i(TAG, "filesize:" +fileSize);
Log.i(TAG, "filepath:" +filepath);
}
catch(IOException e1){
e1.printStackTrace();
}
return null;
}
#Override
protected void onPreExecute(){
super.onPreExecute();
pDialog.show();
}
#Override
protected void onProgressUpdate(Integer... progress){
super.onProgressUpdate(progress);
pDialog.setProgress(progress[0]);
}
protected void onPostExecute(String result){
super.onPostExecute(result);
pDialog.dismiss();
}
}
Edit
Now the application able to download images according and the progress bar is working as well! But I got another issue is how to return error message when the application failed to complete the download. Currently when the application failed to download it will crash. I believed that I should not run it inside the doInBackground side. But where else can I do the checking? Any idea how to return as an error message and request for the user to retry instead of crashing the application?

You never called onProgressUpdate during your doInBackGround(...). Please note that running multiple instances of AsyncTask is a bad idea. Here is what I suggest:
if(isSyncSuccess){
SetConstant.IMAGE_EXIST=1;
pDialog=new ProgressDialog(GalleryScreen.this);
pDialog.setMessage("Downloading file. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setProgress(0);
pDialog.setMax(contentId.length);
pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pDialog.setCancelable(true);
new DownloadFile().execute();
}
private class DownloadFiles extends AsyncTask<String, Integer, String> {
#Override
protected String doInBackground(String... sUrl) {
Bitmap bm;
InputStream in;
if (contentId.length > 0) {
for (int i = 0; i < contentId.length; i++) {
if (helper.databaseChecking(useremail, contentId[i])) {
contentdownload = i;
SetConstant.CONTENT_ID = contentId[i];
String URL = SetConstant.URL_DOWNLOAD_CONTENT + contentId[i];
//YOUR INTRESTING LOOP HERE.
publishProgress(30);
//SOME INTRESTING NUMBER FOR PROGRESS UPDATE
}
}
try {
in = new java.net.URL(sUrl[0]).openStream();
bm = BitmapFactory.decodeStream(new PatchInputStream(in));
File storage = new File(Environment.getExternalStorageDirectory() + File.separator + "/Image/");
Log.i(TAG, "storage:" + storage);
Log.i(TAG, "storage:" + storage.getAbsolutePath());
if (!storage.exists()) {
storage.mkdirs();
}
String FileName = "/" + SetConstant.CONTENT_ID + ".jpg";
FileOutputStream fos = new FileOutputStream(storage + FileName);
bm.compress(Bitmap.CompressFormat.JPEG, 85, fos);
String filepath = storage + FileName;
File filecheck = new File(filepath);
long fileSize = filecheck.length();
fos.flush();
fos.close();
} catch (IOException e1) {
e1.printStackTrace();
}
return null;
}
#Override
protected void onPreExecute () {
super.onPreExecute();
pDialog.show();
}
#Override
protected void onProgressUpdate (Integer...progress){
super.onProgressUpdate(progress);
pDialog.setProgress(progress[0]);
}
protected void onPostExecute (String result){
super.onPostExecute(result);
pDialog.dismiss();
}
}
}
Of course this code don't run and you need to fix the scopes. But what I am trying to suggest is that your loop should be in doInBackGround(...), you should only have 1 instance of AsyncTask at given time for this case, and call the onProgressUpdate().

Primary issue :
SetConstant.CONTENT_ID = contentId[i];
String URL = SetConstant.URL_DOWNLOAD_CONTENT+contentId[i];
Here, you are facing trouble. As #Sofi Software LLC's answer, you are using a global variable, whose value is being changed by the main thread, in another thread.
Secondary Issue :
If you want a progress bar to update, you have to update its value;
it doesn't update itself.
You do need to download the image in AsyncTask (Downloading from URL). Effectively to achieve your functionality, you need to do
Create AsyncTask to download your image (implement download in
doInBackground()), also have a boolean (say isImageDownloaded) to
track if the image is successfully downloaded in postExecute().
Don't forget to also show your progress bar before initiating the
download
Execute your AsyncTask to initiate download
Create extension of android.os.CountDownTimer to countdown a minimum
time
On the method onFinish() check the boolean that you track, if it is
false then you cancel the AsyncTask and throw the toast/dialog that
you intended
Running multipule instance of AsyncTask is not a good idea, so do one after another. You can execute your AsyncTask's on an Executor using executeOnExecutor().To make sure that the threads are running in a serial fashion please use: SERIAL_EXECUTOR.
Following resources may help you #
If you need to download an image, show progress bar and load in a imageview
https://github.com/koush/UrlImageViewHelper
http://developer.aiwgame.com/imageview-show-image-from-url-on-android-4-0.html
http://blog.blundell-apps.com/imageview-with-loading-spinner/
If you need to download multiple files (here, for images) using AsyncTask
Problem with downloading multiple files using AsyncTask
How to get back the task completion status in AsyncTask
Implement Progress Bar for File Download in Android
EDIT:
From http://developer.aiwgame.com/imageview-show-image-from-url-on-android-4-0.html
new DownloadImageTask((ImageView) findViewById(R.id.imageView1))
.execute("http://java.sogeti.nl/JavaBlog/wp-content/uploads/2009/04/android_icon_256.png"); }
public void onClick(View v) {
startActivity(new Intent(this, IndexActivity.class));
finish();
}
private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
ImageView bmImage;
public DownloadImageTask(ImageView bmImage) {
this.bmImage = bmImage;
}
protected Bitmap doInBackground(String... urls) {
String urldisplay = urls[0];
Bitmap mIcon11 = null;
try {
InputStream in = new java.net.URL(urldisplay).openStream();
mIcon11 = BitmapFactory.decodeStream(in);
} catch (Exception e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return mIcon11;
}
protected void onPostExecute(Bitmap result) {
bmImage.setImageBitmap(result);
} }
From Image download in an Android ImageView and Progressbar implementation
// note that you could also use other timer related class in Android aside from this CountDownTimer, I prefer this class because I could do something on every interval basis
// tick every 10 secs (or what you think is necessary)
CountDownTimer timer = new CountDownTimer(30000, 10000) {
#Override
public void onFinish() {
// check the boolean, if it is false, throw toast/dialog
}
#Override
public void onTick(long millisUntilFinished) {
// you could alternatively update anything you want every tick of the interval that you specified
}
};
timer.start()

In the following line:
SetConstant.CONTENT_ID = contentId[i];
You're setting a global variable to a value, then you create a string url based on that same value and pass it to the AsyncTask. That executes, and then when it is done downloading, it create a file whose name is based on the global variable SetConstant.CONTENT_ID.
In other words, you are using a global variable, whose value is being changed by the main thread, in another thread. Don't do this, as you will get all kinds of weird problems due to the different threads updating at different times.. Pass in the value or the name of the output file to the AsyncTask. You can do that in a constructor for DownloadFile, and stash the value in a field.
If you want a progress bar to update, you have to update its value; it doesn't update itself. Call AsyncTask.publishProgress during the task (in doInBackground) and implement onProgressUpdate to update the progress dialog.
[EDIT: onProgressUpdate is indeed called in the UI thread.]

First create a separated class which allows you to reach to image address
like following:
public class ImageDownloader extends AsyncTask {
#Override
protected Bitmap doInBackground(String... urls) {
try {
URL url = new URL(urls[0]);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream inputStream = connection.getInputStream();
Bitmap myBitmap = BitmapFactory.decodeStream(inputStream);
return myBitmap;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}
Then get access to that class (through a method called by a button) by creating an object and execute the Bitmap task like following :
public class MainActivity extends Activity {
ImageView downloadedImg;
public void downloadImage(View view) {
ImageDownloader task = new ImageDownloader();
Bitmap myImage;
try {
myImage = task.execute("YOUR IMAGE ADDRESS ........").get();
downloadedImg.setImageBitmap(myImage);
} catch (Exception e) {
e.printStackTrace();
}
}
Do NOT forget to:
1 - define the imageView in onCreat method ==> downloadedImg = (ImageView) findViewById(R.id.imageView);
2 - to link the method you've created by a button in user interface ==> (public void downloadImage(View view){})
3 - ask for permission in manifest file

How to get the data from remote database to android quickly?

I am displaying the student details from remote MSSQL database into android using php scripts. The data is displaying fine but it is taking more time to display them i.e until the data is displayed it is showing black screen. How to get the data quickly and where should I make the changes to avoid the black screen?
Thanks in advance.

You should pull the Data Asynchronously. Refer to AsyncTask. If the remote call is so slow you can also think about some caching.
new Thread(new Runnable() {
#Override
public void run() {
//loaddata
}
}).start();
keep in mind that when you want to access the UI Thread you have to use the runOnUiThread method
In Android every App can have a Caching Directory. Its a good way to cache your Data and display this data for the time the fresh data is loading in the Background.
With your Datastructure Serializable you be able to write down your Data into this Caching Directory and speed up your Loading.
Here some Snippeds for Caching data:
private void loadData() {
ObjectInputStream in;
try {
FileInputStream fis = new FileInputStream(new File(getCacheDir(),
"cache.dat"));
in = new ObjectInputStream(fis);
data = (Data) in.readObject();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
private void saveData() {
if (data.size() > 0) {
File file = new File(getCacheDir(), "cache.dat");
ObjectOutputStream out;
try {
file.createNewFile();
out = new ObjectOutputStream(new FileOutputStream(file));
out.writeObject(data);
out.close();
} catch (IOException e) {
}
}
}