Android service cannot connect to web service when app is closed

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Android

service

webservice

I am developing an application which connects to a web service via the internet and gets some information and I've used Async task for this in two activities. Now I want to use the same code in a service class which works with Timer task and on every tick, if the application is not running, it should return some data from web service. I can retrieve data when the app is open, but when I close it, I get "Connection to foo.com is refused"!

public void initializeTimerTask() {

    timerTask = new TimerTask() {
        public void run() {

            //use a handler to run a toast that shows the current timestamp
            handler.post(new Runnable() {
                public void run() {if(!isAppRunning(getApplicationContext(),getPackageName())) {

                            new ExecuteTask().execute();
                        }

                }
            });
        }
    };
}

class ExecuteTask extends AsyncTask<String, Void, String> {


    @Override
    protected void onPreExecute() {
        super.onPreExecute();

    }


    @Override
    protected void onCancelled() {
        super.onCancelled();
    }


    @Override
    protected String doInBackground(String... params) {

        String res1="";
        try {
                res1 = PostData();

        } catch (Exception ex) {
        }
        return res1;
    }


    @Override
    protected void onPostExecute(String result) {

        if (!isCancelled()) {
            Log.d("responsed", result);

            try {

                int Ifrom = result.indexOf("[");
                int ITo = result.lastIndexOf("]");
                if (Ifrom > -1 && ITo > -1) {
                    result = result.substring(Ifrom, ITo + 1);
                    Log.d("test", result);
                }

                android.util.JsonReader reader = new android.util.JsonReader(new StringReader(result));
                reader.setLenient(true);
                Type listType = new Type() {
                };

                listType = new TypeToken<List<alarms>>() {
                }.getType();
                List<alarms> lstAlarms = new ArrayList<alarms>();
                lstAlarms = new Gson().fromJson(result, listType);

                //if there is new alarm then show notifications
                if(lstAlarms.size()>0)

            } catch (Exception ex)

            {
            }

        }

    }
}


public String PostData() {
    String s = "";
    try {
        HttpClient httpClient = new DefaultHttpClient();
        String Url = "";
            Url = settingsWeb.getString("Address", null);
        List<namevaluepair> nameValuePairs = new ArrayList<namevaluepair>();

        nameValuePairs.add(new BasicNameValuePair("JsonQuery",Command);
        Url += "/SelectJsonAlarms";


        HttpPost httppost = new HttpPost(Url);
        httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
        HttpResponse response = httpClient.execute(httppost);

        s = readResponse(response);
    } catch (Exception e) {
        return "error";
    }

    return s;

}

What I have tried:

I have uses-permission android:name="android.permission.INTERNET" in my Android manifest.
I get the error on this line ==> HttpResponse response = httpClient.execute(httppost);