Develop Reference

Saving objects in cache

I am trying to save in cache response from server for certain time.
There are tne next data for saving in cache: I have a List<ProgrammeItem> which I am getting from server. While user is working, he can download up to ~230 List<ProgrammeItem> (but it is unreal to reach this, estimated is 10-50).
ProgrammeItem oblect including strings, int, int[].
That is how I am saving and getting the last downloaded List<ProgrammeItem>:
//saving / getting Programme items
public boolean saveObject(List<ProgrammeItem> obj) {
final File suspend_f=new File(android.os.Environment.getExternalStorageDirectory(), "test");
FileOutputStream fos = null;
ObjectOutputStream oos = null;
boolean keep = true;
try {
fos = new FileOutputStream(suspend_f);
oos = new ObjectOutputStream(fos);
oos.writeObject(obj);
} catch (Exception e) {
keep = false;
Log.e("catching exception ", "" + e.getMessage() + ";;;" + e);
} finally {
try {
if (oos != null) oos.close();
if (fos != null) fos.close();
if (keep == false) suspend_f.delete();
} catch (Exception e) { /* do nothing */ }
}
return keep;
}
public List<ProgrammeItem> getObject(Context c) {
final File suspend_f=new File(android.os.Environment.getExternalStorageDirectory(), "test");
List<ProgrammeItem> simpleClass= null;
FileInputStream fis = null;
ObjectInputStream is = null;
try {
fis = new FileInputStream(suspend_f);
is = new ObjectInputStream(fis);
simpleClass = (List<ProgrammeItem>) is.readObject();
} catch(Exception e) {
String val= e.getMessage();
} finally {
try {
if (fis != null) fis.close();
if (is != null) is.close();
} catch (Exception e) { }
}
return simpleClass;
}
That is how I am saving and getting object in activity:
PI = new ProgrammeItem();
List<ProgrammeItem> programmeItems = new ArrayList<>();
...
//filling programmeItems with data from server
...
boolean result = PI.saveObject(programmeItems); //Save object
ProgrammeItem m = new ProgrammeItem();
List<ProgrammeItem> c = m.getObject(getApplicationContext()); //Get object
The question is: how can I save a lot of my objects instead of only one?
I think I should done something like public boolean addObjectsInCache(List<ProgrammeItem> obj) for adding objects, not overriding them.
And change get method into public List<ProgrammeItem> getObject(Context c, String id), where id will be unique identifier, which will includes into every ProgrammeItem in the every List<ProgrammeItem>.
Am I right? And how I can achieve this? Maybe you will show me the other way to work with objects and cache?

You can use SharedPreference instead, while having a local database Android Room can also be an option. SharedPreference basically is stored in your device's cache while the local database is stored in your device's data hence in our apps we have clear cache and clear data function.
Additional Resources:
StackOverFlow: How Android SharedPreferences save/store object
Object based preference library: https://github.com/ShawnLin013/PreferencesManager I would suggest you go with this one, since it can easily save you time saving list based object and retrieving them. You can also add more to the persisted list object when needed.
Secured Preferences: https://github.com/scottyab/secure-preferences

An option could be to use Room database with inMemoryDatabaseBuilder:
db = Room.inMemoryDatabaseBuilder(context, ProgrammeDatabase::class.java)
.build()
if it all can fit in memory.

Dropbox api v2 for Android: how to get media files details?

How to get media files and their details with Dropbox API v2 for Android(Java)? I have gone through the documentation for the FileMetadata , but I couldn't find the methods to get file details like file type(e.g. music, video, photo, text, ...) , file's URL and thumbnail.
this is my folders and files list Asyntask:
//login
DbxClientV2 client = DropboxClient.getClient(accessToken);
// Get files and folder metadata from root directory
String path = "";
TreeMap<String, Metadata> children = new TreeMap<>();
try {
try {
result = client.files().listFolder(path);
arrayList = new ArrayList<>();
//arrayList.add("/");
while (true) {
int i = 0;
for (Metadata md : result.getEntries()) {
if (md instanceof DeletedMetadata) {
children.remove(md.getPathLower());
} else {
String fileOrFolder = md.getPathLower();
children.put(fileOrFolder, md);
//if (!fileOrFolder.contains("."))//is a file
arrayList.add(fileOrFolder);
if (md instanceof FileMetadata) {
FileMetadata file = (FileMetadata) md;
//I need something like file.mineType, file.url, file.thumbnail
file.getParentSharedFolderId();
file.getName();
file.getPathLower();
file.getPathDisplay();
file.getClientModified();
file.getServerModified();
file.getSize();//in bytes
MediaInfo mInfo = file.getMediaInfo();//Additional information if the file is a photo or video, null if not present
MediaInfo.Tag tag;
if (mInfo != null) {
tag = mInfo.tag();}
}
}
i++;
}
if (!result.getHasMore()) break;
try {
result = client.files().listFolderContinue(result.getCursor());//what is this for ?
} catch (ListFolderContinueErrorException ex) {
ex.printStackTrace();
}
}
} catch (ListFolderErrorException ex) {
ex.printStackTrace();
}
} catch (DbxException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
return result;

If you want media information, you should use listFolderBuilder to get a ListFolderBuilder object. You can use call .withIncludeMediaInfo(true) to set the parameter for media information, and then .start() to make the API call. The results will then have the media information set, where available.
Dropbox API v2 doesn't offer mime types, but you can keep your own file extension to mime type mapping as desired.
To get an existing link for a file, use listSharedLinks. To create a new one, use createSharedLinkWithSettings.
To get a thumbnail for a file, use getThumbnail.

Threads, atomic boolean, synchronized design considerations for a method that has to wait for a result

My code is starting to get a bit hard to debug which leads me to believe that my design choices are not ideal. I am a novice Android programming and would love some help with streamlining the design for optimum operation.
Intro
I am writing an application that uses rfcomm interface to transfer data between a client and server device. The client needs to request certain things from the server using a specific key, then it needs to wait until the server sends the result back.
Current Design
A button press triggers a request for information from the server.
A new thread is started which performs the request.
A key which is a unique integer is converted to a byte array and sent to the server.
Thread has a while loop that is waiting for a specific boolean to flip from false to true indicating a response back from the server.
Information is received on the server side. Server uses key to identify what to do next.
server starts a thread to run some query and gets a jsonString back as a result.
Server sends jsonstring converted to byte array prepended with the same identifying key back to the client.
Client reads message, and sends the byte array to a handling method based on the identifying key.
Handling method stores jsonString to a class variable and then flips the boolean to let the other thread know that the value it was waiting on has been set.
Json string is converted to object on the client side. Something is done with that object.
This code currently correctly sends info to the server, server correctly does search and gets a valid json string result. However, the issue occurs when the server writes its results make to the client. I am getting 20 messages instead of one and none match the search key...
My questions
Am I doing things in an efficient way design wise?
Can I benefit from using synchronized keyword or and Atomic Boolean to make my code more thread safe? How would I go about implementing it?
Is there a max length for converting strings to byte array? Maybe the code is trying to break up the sending for me and that's why I'm getting 20 different results?
Relevant code
public class ClientSpokesmanClass {
private final int searchKey = 2222222; //set the key to some int.
private boolean pendingSearchResults = false;
List<Place> places = new ArrayList<Place>();
private final Handler handler = new Handler(){
#Override
public void handleMessage(Message msg){
switch(msg.what) {
...
case MESSAGE_READ:
//Message received from server
readAndDistribute(msg.arg1, msg.obj);
break;
...
}
}
};
public List<Place> getPlacesFromServer(String query){
//ask server for search results
requestSearchFromServer(query);
//just wait for them...
while (pendingSearchResults){
//just waiting
}
return places;
}
private void requestSearchFromConnectedDevice(String query) {
if (mBluetoothState == STATE_CONNECTED){
byte[] bites = new byte[4];
bites = ByteBuffer.wrap(bites).putInt(searchKey).array();
byte[] stringBytes = null;
try {
stringBytes = query.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
Log.e(TAG, "unsupported encoding", e);
}
int keyLength = bites.length;
int stringLength = stringBytes.length;
byte[] combined = new byte[keyLength+stringLength];
System.arraycopy(bites, 0, combined, 0, keyLength);
System.arraycopy(stringBytes, 0, combined, keyLength, stringLength);
mBluetoothService.write(combined);
}
pendingSearchResults = true;
}
private void receiveSearchResults(byte[] bites){
String jsonString = "";
PlacesJSONParser parser = new PlacesJSONParser();
try {
jsonString = new String(bites, "UTF-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
Log.e(TAG, "unsupported encoding", e);
}
if (D) Log.d(TAG, "Json string we got is "+jsonString);
try {
places = parser.parse(new JSONObject(jsonString));
} catch (JSONException e) {
// TODO Auto-generated catch block
Log.e(TAG, "JSON exception", e);
}
pendingSearchResults = false;
}
/**
* Reads come here first. Then, based on the key prepended to them,
* they then go to other methods for further work.
* #param bytes
* #param buffer
*/
private synchronized void readAndDistribute(int bytes, Object buffer){
byte[] buff = (byte[]) buffer;
int key = ByteBuffer.wrap(Arrays.copyOfRange(buff, 0, 4)).getInt();
if (key == searchKey){
receiveSearchResults(Arrays.copyOfRange(buff, 4, bytes));
}else{
//do something else
}
}
}
.
public class ClientUI extends Activity {
...
onQueryTextSubmit(String query){
final String queryFinal = query;
Thread thread = new Thread(){
public void run() {
places = ClientSpokesmanClass.getPlacesFromServer(query);
doSomethingWithPlaces();
}
};
thread.start();
}
}
.
public class ServerReceive {
private searchKey = 2222222;
...
//code that handles messages, reads key, and then runs doSearchAndWriteResults()
...
private synchronized void doSearchAndWriteResults(byte[] bites){
if (D) Log.d(TAG, "+++writeSearchResults");
//Initialize query and placesString
String query = null;
String placesString;
//Convert byte array to the query string
try {
query = new String(bites, "UTF-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
Log.e(TAG, "unsupported encoding",e);
}
//if the string was converted successfully...
if (query != null){
//Run the places query and set the json string to placesString
if (D) Log.d(TAG, "query is "+query);
PlacesProvider placeProvider = new PlacesProvider();
placesString = placeProvider.getPlacesString(query);
}
//initialize a bite array
byte[] stringBytes = null;
try {
//convert jsonString to byte array
stringBytes = placesString.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
Log.e(TAG, "unsupported encoding",e);
}
//Put the search key to a byte array. I am using this key on the client side
//to confirm that we are reading searchResults and not some other type of write.
byte[] bite = new byte[4];
bite = ByteBuffer.wrap(bite).putInt(searchKey).array();
//Get the lengths of the two byte arrays
int keyLength = bite.length;
int stringLength = stringBytes.length;
//combine the byte arrays for sending
byte[] combined = new byte[keyLength+stringLength];
System.arraycopy(bite, 0, combined, 0, keyLength);
System.arraycopy(stringBytes, 0, combined, keyLength, stringLength);
if (D) Log.d(TAG, "Actually writing things here...");
//send the byte arrrays over rfcomm
mBluetoothService.write(combined);
}
}

Take a look at https://github.com/gettyimages/connect_sdk_java. Specifically, at the test application. It performs a search using an AsyncTask and the private class notifies the UI via onPostExecute. Hopefully, this will get you further along.

Write whole Android shared_preferences.xml at once

Is it possible to write a whole shared_preferences.xml at once?
I want to realize a kind of settings import/export, so i need to read and write the whole file without loosing the xml-tags.
Reading the file is easy, but when i write my values (using PrintWriter) the old values stored in memory overwrite them seconds later.
what can i do to prevent that without writing single values using preference editor.

Now I read it from a file designed like Android's own preferences.xml and write it successively in my own function like this:
public static void preferencesImport(String PreferenceFilepath) {
preferencesImportPreferenceFilepath = PreferenceFilepath;
try {
// Parsing
// see http://theopentutorials.com/tutorials/android/xml/android-simple-xml-dom-parser/
XMLParserHelper parser = new XMLParserHelper(); // reference to described XMLDOMParser helper class
BufferedInputStream stream;
try {
stream = new BufferedInputStream(new FileInputStream(preferencesImportPreferenceFilepath));
org.w3c.dom.Document doc = parser.getDocument(stream);
// string value
NodeList nodeListString = doc.getElementsByTagName("string");
for (int i = 0; i < nodeListString.getLength(); i++) {
Element eString = (Element) nodeListString.item(i);
Pref.setString(eString.getAttribute("name"), eString.getTextContent()); // Own getter/setter -> use Android's preference manager instead in similar way
}
// repeat code above for boolean, long, int, float values
stream.close();
} catch (IOException e1) {
// output IOException
} catch (Throwable t1) {
// output Throwable1
}
writer.close();
} catch (Throwable t2) {
// output Throwable2
}
}

Problem Reading Saved File : Android

I am read & write username & password to android device using my application to internal storage. I am successful writing to the device, but while reading I get error. On start of the aplication I read that file and I get "The applicaton (...) has stopped unexpectedly. Please try again." with "Force Close" button and the app closes. I tried different ways to read, but all showed same results. I write my data as username + "\n" + passwrd + "\n". This is the code for reading data :
private static String ReadFromFile(String fileName) {
String text = "";
FileInputStream fis = null;
byte[] fileData;
try {
StringBuffer sb = new StringBuffer();
int c = 0;
fis = AppContext.openFileInput(fileName);
if (fis.available() != 0) {
fileData = new byte[fis.available()];
c = fis.read(fileData);
Log.i(TAG, "Read Byes = " + c );
java.util.StringTokenizer stk = new java.util.StringTokenizer(new String(fileData), "\n");
text = stk.toString();
} else
throw new IOException("fis.available() <= 0"); /*
c = (char)fis.read();
while (c != -1){
if (c != -1)
sb.append(c);
c = (char)fis.read();
}
text = sb.toString();
*/
fis.close();
} catch (FileNotFoundException e) {
text = "null " + e.getMessage();
} catch (IOException e) {
text = "null " + e.getMessage();
} finally {
fis = null;
}
return text;
}
/*
try {
StringBuffer sb = new StringBuffer();
RandomAccessFile raf = new RandomAccessFile(ENC_LOGIN_FILE, "r");
while ((str1 = raf.readLine()) != null){
sb.append(str1);
}
str1 = sb.toString();
} catch (FileNotFoundException e) {
errorMessage = "File Not Found: " + e.getMessage();
//e.printStackTrace();
} catch (IOException ioe) {
errorMessage = "IOExcp: " + ioe.getMessage();
//e.printStackTrace();
}*/
No path is used and the filename directly is given to write & read file. I checked out Problem facing in reading file from Internal memory of android from where I tried StringTokenizer.
Can anyone help me know where am I going wrong. The following permission are set :
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.WRITE_SECURE_SETTINGS"></uses-permission>
<uses-permission android:name="android.permission.WRITE_SETTINGS"></uses-permission>
<uses-permission android:name="android.permission.WRITE_SYNC_SETTINGS"></uses-permission>
<uses-permission android:name="android.permission.READ_SYNC_SETTINGS"></uses-permission>
<uses-permission android:name="android.permission.READ_SYNC_STATS"></uses-permission>
<uses-permission android:name="android.permission.READ_LOGS"></uses-permission>
Also how do I debug the application. How to check the data written in Log. If I use SOP, where does it dispaly - it doesn't display in Console window ? Please help me, I am n newbie in android development.
One more thing to clarify : My motto is to store username and password in such a way that user must not be able to read them directly. I have already used MODE_PRIMITIVE. Is their a need to use JSONObject to save this data. I had a look at JSON in couple of sites & API but couldn't make out why and where it should be used. Using MODE_PRIMITIVE I believe even the user can't read the file. Only my application can read it. Then I don't think I should use JSON. Please correct me if I am wrong.
Any help is highly appreciated.
Thanks.

A suggestion:
If you are only saving username and password then use SharedPreferences instead of saving the data in a file. It is a much secure way and plus very hassle free.
Use this blog article on How to use Shared Preferences:
http://saigeethamn.blogspot.com/2009/10/shared-preferences-android-developer.html

fis = AppContext.openFileInput(fileName);
fileData = new byte[fis.available()];
java.util.StringTokenizer stk =
new java.util.StringTokenizer(new String(fileData), "\n");
It appears to me that you're trying to create a new String using an uninitialized array as input. You've asked for the array to be a specific size, but you haven't done anything to read data into the array. (Note that available() only asks for the size of the data that can be read without blocking; it doesn't actually read the data. For that you need the read() method.)
Try this:
fis = AppContext.openFileInput(fileName);
fileData = new byte[fis.available()];
fis.read(fileData);
java.util.StringTokenizer stk =
new java.util.StringTokenizer(new String(fileData), "\n");
You should check the return value of fis.read(), but give this a try to see if it lets you progress further.