Develop Reference

How can I improve the speed of retrieving data from internet in an AsyncTask?

In my following code I am trying to retrieve some JSON data by passing an URL. It works fine but does take some time in fetching data from the Internet. Even though the data isn't that bulky but still it takes like few seconds and then I can see data in log. But I really want to improve the speed with which I could improve retrieving data from internet.
public class DownloadData extends AsyncTask<String, Void, String> {
private static final String TAG = "DownloadData";
#Override
protected String doInBackground(String... strings) {
try {
URL url = new URL(strings[0]);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("GET");
httpURLConnection.connect();
InputStream inputStream = httpURLConnection.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
String result = "";
int data;
data = inputStreamReader.read();
while (data != -1) {
char currentChar = (char) data;
result += currentChar;
data = inputStreamReader.read();
}
return result;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return "Failed";
}
#Override
protected void onPostExecute(String s) {
Log.d(TAG, "downloaded JSON Data: " + s);
}
}

Dont read characters one by one. Takes too much time. Use .readLine() instead.
Dont use string concatenation as that takes a lot of time too. Instead use a StringBuilder to add the lines to.

Screen freezes when downloading content from server in android

I am downloading JSON Content from server in the MainActivity and passing the JSON from MainActivity to ListActivity, the problem here is I have added a sleep time of 10s in the backend server i.e. Php from where the data is fetched. Since, the response will the delayed I would expect that screen opens and waits until the response comes and move to next screen.
But what is happening is the screen goes white/black completely untill the response is recieved and ListActivity is loaded, the problem here is the MainActivity is never visible. Below is code for the same:
MainActivity
JSONData jsonData = new JSONData();
String jsonList = jsonData.fetchList();
Intent intent = new Intent(getApplicationContext(),ListActivity.class);
intent.putExtra("jsonList",jsonList);
startActivity(intent);
finish();
JSON Data class
public String fetchList() {
try {
String list = new DownloadJSONData().execute(listURL).get().toString();
return list;
} catch (Exception e) {
return "";
}
}
private class DownloadJSONData extends AsyncTask<String, String, String> {
protected void onPreExecute() {
super.onPreExecute();
}
protected String doInBackground(String... params) {
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
StringBuffer buffer = new StringBuffer();
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line + "\n");
}
return buffer.toString();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return "";
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
}
}

you are using get() method which accquires the main thread or ui thread untill the async task is completed
you should avoid using get() and also can use progress dialog in onPreExecute for displaying progression on network call to user

HttpURLConnection crashes application

I want to receive and send data with a web server but the code does not work
What do I do for this code to work?
Note this code inside onCreate
try {
URL url = new URL("http://myweb.com/");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
InputStream Stream = connection.getInputStream();
InputStreamReader reader = new InputStreamReader(Stream);
BufferedReader b = new BufferedReader(reader);
StringBuilder s = new StringBuilder();
String str ="";
while ((str = b.readLine())!=null) {
s.append(str);
}
String data = s.toString();
TextView myText = (TextView) findViewById(R.id.Text);
myText.setText(data);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

Make sure that you do network-related tasks on a separate thread in Android. Also, check that you have the INTERNET permission set.
If you want to then update the UI from another thread, you have to use
runOnUiThread (new Runnable () {
public void run() {
//update ui in here
}
}

All your code runs in Main thread which should be always used for setting up the UI and to listen for UI events such as on click listeners.
Network calls are not allowed on this thread as they might take long time. Use AsyncTask API of android which is designed for running code in separate thread.
Create a class like one below for all GET request tasks.
public class DownloadTask extends AsyncTask<String, Void, Integer> {
private String TAG = "InDownloadTask";
private DownloadCallback callback;
private String data;
public DownloadTask(DownloadCallback cb){
callback = cb;
}
#Override
protected Integer doInBackground(String... params) {
Integer result = 0;
HttpURLConnection urlConnection;
try {
URL url = new URL(params[0]);
urlConnection = (HttpURLConnection) url.openConnection();
int statusCode = urlConnection.getResponseCode();
if (statusCode == 200) {
BufferedReader r = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
StringBuilder response = new StringBuilder();
String line;
while ((line = r.readLine()) != null) {
response.append(line);
}
data = response.toString();
result = 1;
} else {
result = 0;
}
} catch (Exception e) {
Log.d(TAG, e.getLocalizedMessage());
}
return result;
}
#Override
protected void onPostExecute(Integer integer) {
super.onPostExecute(integer);
callback.onFinishDownload(data, integer);
}
}
Create a callback interface that we use for the above class.
public interface DownloadCallback {
public void onFinishDownload(String data, Integer result);
}
Now from your activity onCreate
String url = "http://myweb.com/";
new DownloadTask(new DownloadCallback() {
public void onFinishDownload(String data, Integer result) {
if(result == 1)
myText.setText(data);
else
myText.setText("Error");
}
}).execute(url);
If you have many network related operations, use a Network library such as Volley which will take care of this.

AsyncTask usage on Android

I use AsnycTask to connect URL and parse the return xml:
class Connecting extends AsyncTask<String, String, String> {
private String URLPath = "";
private HttpURLConnection Connection;
private InputStream InputStream;
private boolean Return1 = false;
private int Return2 = -1;
public Connecting (String fn, String u) {
FileName = fn;
URLPath = u;
Connection = null;
InputStream = null;
Return1 = false;
Return2 = -1;
execute();
}
public boolean getReturn1() {
return Return1;
}
public int getReturn2() {
return Return2;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected String doInBackground(String... aurl) {
try {
URL url = new URL(URLPath);
Connection = (HttpURLConnection)url.openConnection();
Connection.setConnectTimeout(10000);
Connection.setReadTimeout(10000);
Connection.setDoInput(true);
Connection.setUseCaches(false);
Connection.connect();
InputStream = Connection.getInputStream();
}
catch (Exception e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(String unused) {
super.onPostExecute(unused);
try {
InputStreamReader fsr = new InputStreamReader(InputStream);
BufferedReader br = new BufferedReader(fsr);
String line = "";
while((line = br.readLine()) != null) {
//parse Reture1 and Return2
}
}
catch(Exception e) {
e.printStackTrace();
}
Connection = null;
}
}
And I use below code to call it:
Connecting con = new Connecting(Name, URL);
System.out.println("Return1 " + con.getReturn1());
System.out.println("Return2 " + con.getReturn2());
It will get false and -1, which the init value.
And connect URL after print message.
I want to get the value which has connect success and parse from the xml.
How can I do it?

AsyncTask is a class that helps to run in background. You can use it if you want to access to remote server using for example HTTP connection.
In doBackground method you have to the the "heavy" task, the one that requires time and could block the UI. When you finish at the end of doBackground you have to return the value that is the result of the task.
Then in the onPostExecute you use this result to update for example the UI.
In your case it seems to me you aren't using correctly the AsyncTask. First of all you return null in doBackground and dont set return1 and return2 as you should.
And in onPostExecute you read the response while yuo should do it in doBackground.
There's another method you can override called onPreExecute that is called before doBackground method.
In my blog i've an example how to use AsyncBackground in this case and it could help you. If you like give a look here

The AsyncTask runs (as the name says) asynchronously to the main-thread.
If you want to happen something after the task is done, you have to put that code in the onPostExecute() method.
So you may put the System.out there.

SocketTimeoutException awaited but not thrown?

I'm writing an Android app which receives data from a server. Theoretical there could not be an internet connection so I try to catch this case by catching a SocketTimeoutException to show an error message an a retry screen or something else. Unfortunately this exception won't be thrown. At least it doesn't jump into the catch clause. What am I doing wrong?
public class HttpConnector {
private String urlString;
private int connectionTimeout = 5000; //milliseconds
public HttpConnector(String urlString) {
this.urlString = urlString;
}
public String receiveData() throws PolizeiwarnungException {
URL url = null;
HttpURLConnection urlConnection = null;
StringBuffer b = new StringBuffer();
try {
url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setReadTimeout(connectionTimeout);
BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream())); //Here it gets stuck if there is no connection to the server
String str;
while ((str = reader.readLine()) != null) {
b.append(str + "\n");
}
}
catch (SocketTimeoutException e) {
//TODO
e.printStackTrace();
}
catch (IOException e) {
throw new PolizeiwarnungException(e);
}
finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
}
return b.toString();
}
public void sendData(String data) {
//TODO
}
}

You need to also set the connect timeout. Please see this documentation.
Since the end point does not exist, without having set a connect time out the connection will never time out.
setConnectTimeout(int timeout) Sets the timeout value in milliseconds
for establishing the connection to the resource pointed by
this URLConnection instance.