Use SharedPreferences in service has Nullpointerexception

Use SharedPreferences in service has Nullpointerexception

I would like to develop a program to upload file to Dropbox automatically
in background.
I find that it cannot get the Shared preference key after reboot and
return Nullpointerexception. Would you guys please help to find out the
reason and solution?
public class Upload extends Service {
private File mFile = new
File(Environment.getExternalStorageDirectory()+"test.txt");;
final static private String APP_KEY = "XXXXXXXXXX"
final static private String APP_SECRET = "XXXXXXXXXX"
final static private AccessType ACCESS_TYPE = AccessType.DROPBOX;
///////////////////////////////////////////////////////////////////////////
// End app-specific settings.
//
///////////////////////////////////////////////////////////////////////////
// You don't need to change these, leave them alone.
final static private String ACCOUNT_PREFS_NAME = "prefs";
final static private String ACCESS_KEY_NAME = "ACCESS_KEY";
final static private String ACCESS_SECRET_NAME = "ACCESS_SECRET";
AppKeyPair appKeys = new AppKeyPair(APP_KEY, APP_SECRET);
// AndroidAuthSession session = new AndroidAuthSession(appKeys,
ACCESS_TYPE);
AndroidAuthSession session = buildSession();
DropboxAPI<AndroidAuthSession> mDBApi = new
DropboxAPI<AndroidAuthSession>(session);
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
int res = super.onStartCommand(intent, flags, startId);
if (mDBApi.getSession().authenticationSuccessful()){
try {
// Required to complete auth, sets the access token on
the session
mDBApi.getSession().finishAuthentication();
AccessTokenPair tokens =
mDBApi.getSession().getAccessTokenPair();
storeKeys(tokens.key, tokens.secret);
Runnable runnable = new Runnable(){
@Override
public void run() {
try {
uploadtodropbox();
stopSelf();
} catch (Exception e)
{
Log.e("Upload", "Could not Upload to
dropbox", e);
}
}
};
new Thread(runnable).start();
} catch (IllegalStateException e) {
Log.i("DbAuthLog", "Error authenticating", e);
}
}else{
mDBApi.getSession().startAuthentication(this);
try {
uploadtodropbox();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (DropboxException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return res;
}
private void storeKeys(String key, String secret) {
// Save the access key for later
SharedPreferences prefs =
getSharedPreferences(ACCOUNT_PREFS_NAME, 0);
Editor edit = prefs.edit();
edit.putString(ACCESS_KEY_NAME, key);
edit.putString(ACCESS_SECRET_NAME, secret);
edit.commit();
}
private void uploadtodropbox() throws FileNotFoundException,
DropboxException{
FileInputStream fis = new FileInputStream(mFile);
String path = mFile.getName();
mDBApi.putFileOverwrite(path, fis, mFile.length(), new
ProgressListener(){
@Override
public long progressInterval() {
// Update the progress bar every half-second or so
return 500;
}
@Override
public void onProgress(long bytes, long total) {
publishProgress(bytes);
}
});
}
protected void publishProgress(long bytes) {
// TODO Auto-generated method stub
}
/**
* Shows keeping the access keys returned from Trusted Authenticator
in a local
* store, rather than storing user name & password, and
re-authenticating each
* time (which is not to be done, ever).
*/
private void clearKeys() {
SharedPreferences prefs = getSharedPreferences(ACCOUNT_PREFS_NAME, 0);
Editor edit = prefs.edit();
edit.clear();
edit.commit();
}
private String[] getKeys() {
SharedPreferences prefs = getSharedPreferences(ACCOUNT_PREFS_NAME, 0);
String key = prefs.getString(ACCESS_KEY_NAME,null);
String secret = prefs.getString(ACCESS_SECRET_NAME, null);
if (key != null && secret != null) {
String[] ret = new String[2];
ret[0] = key;
ret[1] = secret;
return ret;
} else {
return null;
}
}
AndroidAuthSession buildSession() {
AppKeyPair appKeys = new AppKeyPair(APP_KEY, APP_SECRET);
AndroidAuthSession session;
String[] stored = getKeys();
if (stored != null) {
AccessTokenPair accessToken = new
AccessTokenPair(stored[0], stored[1]);
session = new AndroidAuthSession(appKeys, ACCESS_TYPE,
accessToken);
} else {
session = new AndroidAuthSession(appKeys, ACCESS_TYPE);
}
return session;
};
@Override
public IBinder onBind(Intent intent) {
// TODO Auto-generated method stub
return null;
}
}