Develop Reference

Simplest straight forward way to get a JSON String from a REST URL

I am trying to get a JSON string from a url and save it into SQLite in my android app.
I was trying some tutorials then realize the suggested methods has a void return type. Are there a more simple straight forward way of getting a JSON String and putting it into an arraylist ready to be saved into SQLite?
Below is what I was stuck at a helper class that gets the data from the url
as they said that the main thread OnCreate does not allow a background process like this. Is there a way to change the return type of AsyncTask or is there a more simple way to fetch JSON String with android?
public class FetchData extends AsyncTask<Void, Void, Void> {
#Override
protected void doInBackground(ArrayList<String>... voids) {
try {
URL url = new URL("http://192.168.403.211/api/wordsupdate.php");
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader (new InputStreamReader(inputStream));
String line ="";
while (line != null) {
line = bufferedReader.readLine();
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}

Go with Volley API. Check the code below which demonstrate POST request. Hope you'll get useful information.
public void getAddress(final String uid) {
String url = "Add Url Here"; // Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.POST, url,
new Response.Listener<String>() {
#Override
public void onResponse(String response) {
JSONArray dataArray;
JSONObject jsonObject;
address_ids = new ArrayList<>();
address_names = new ArrayList<>();
address_line1 = new ArrayList<>();
address_line2 = new ArrayList<>();
address_state = new ArrayList<>();
address_district = new ArrayList<>();
address_taluka = new ArrayList<>();
address_pincode = new ArrayList<>();
address_status = new ArrayList<>();
address_default = new ArrayList<>();
try {
jsonObject = new JSONObject(response);
dataArray = jsonObject.getJSONArray(JSON_ARRAY);
//adding response values to respective array
for (int i = 0; i < dataArray.length(); i++) {
//Creating a json object of the current index
JSONObject obj;
try {
//getting json object from current index
obj = dataArray.getJSONObject(i);
address_ids.add(obj.getString(TAG_ADDRESS_ID));
address_names.add(obj.getString(TAG_ADDRESS_NAME));
address_line1.add(obj.getString(TAG_ADDRESSLINE_FIRST));
address_line2.add(obj.getString(TAG_ADDRESSLINE_SECOND));
address_state.add(obj.getString(TAG_STATE));
address_district.add(obj.getString(TAG_DISTRICT));
address_taluka.add(obj.getString(TAG_TALUKA));
address_pincode.add(obj.getString(TAG_PINCODE));
address_status.add(obj.getString(TAG_ADDRESS_STATUS));
} catch (JSONException e) {
e.printStackTrace();
}
}
} catch (JSONException e) {
e.printStackTrace();
}
//setting up response values to the fragment
//Toast.makeText(getActivity(), "Error:"+response, Toast.LENGTH_LONG).show();
Log.e(TAG, "onResponse: " + response);
address_name.setText("Name : " + address_names.get(0));
address.setText("Address : " + address_line1.get(0) + "," + address_line2.get(0) + "-" + address_pincode.get(0));
taluka.setText("Taluka : " + address_taluka.get(0));
district.setText("District : " + address_district.get(0));
state.setText("State : " + address_state.get(0));
mCircularProgressBar.setIndeterminate(false);
}
}, new Response.ErrorListener() {
#Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(getApplication(), "Taking bit longer", Toast.LENGTH_LONG).show();
}
}) {
#Override
protected Map<String, String> getParams() {
Map<String, String> params = new HashMap<String, String>();
params.put("mk_address_id", address_id);
return params;
}
};
queue.add(stringRequest);
}

Check this link from Android developer, you can find more info their.
In your code change the "extends" from
AsyncTask<Void, Void, Void>
to
AsyncTask<Void, Void, String>
and the doInBackground method to
protected String doInBackground(ArrayList<String>... voids)
and you will get the string back in the onPostExecute method

Yes there is a way to change the return types: Have a look at your extends AsyncTask: It says AsyncTask<Void, Void, Void>.
According to Android Developers, this means <Params, Progress, Result>.
This means that your
ArrayList<String>... voids won't work too, because you have the Params part set to Void but try to get an ArrayList<String>.
So, to solve your problem, change the three Voids to whatever you need it to input and output.
However, to deserialize JSON you should use an external library (or use a 3rd party library for REST calls altogether).

//AsyncTask has onPostExecute which will be called after background execution, where you will get the result in mainthread
class FetchData extends AsyncTask<Void, Void, String> {
#Override
protected String doInBackground(Void... voids) {
try {
URL url = new URL("http://192.168.403.211/api/wordsupdate.php");
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder builder = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
builder.append(line);
}
return builder.toString();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(String result) {
//Your result String is here which runs on MAIN THREAD
super.onPostExecute(result);
}
}

Retrofit 2 will help you - easy and simple
Edit : For Async task see the top answer here
What arguments are passed into AsyncTask<arg1, arg2, arg3>?

In your code snippet , you specified AsyncTask params types are Void. Void means , it does't have any return value. As per AsyncTask Syntax,
You have to specify three arguments.
1- InputType- DoInBanckground
2- ProgressType - Publish Progress.
3- OutputType - OnPostExecute.
The three types used by an asynchronous task are the following:
Params, the type of the parameters sent to the task upon execution.
Progress, the type of the progress units published during the background computation.
Result, the type of the result of the background computation.
In your snippet doInBackground method and AsycTask types are mismatching .
For more information : https://developer.android.com/reference/android/os/AsyncTask.html

Async HttpRequest Timing Out

The Problem
I have an AsyncTask task called from an Activity's OnCreate method. This task makes an http request. The HTTP request hangs. Once the "CODE HANGS HERE" code in the code below is executed, I observe in the debugger that the Async threads are perpetually 'running' and never return anything.
The Code
Here's the OnCreate method of the activity:
protected void onCreate(Bundle savedInstanceState) {
asyncRequest.delegate = this;
super.onCreate(savedInstanceState);
setContentView(R.layout.activty_attach);
Button retakeButton = (Button) (findViewById(R.id.retake_button));
retakeButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent intent = new Intent(AttachActivity.this, MainActivity.class);
startActivity(intent);
}
});
try {
URL url;
url = new URL("http://btl-cromwell:9000/api/engine/v1/version");
asyncRequest.execute(url);
} catch (Exception e) {
Log.e(logtag, e.toString());
}
}
Note the URL that is passed to he async task should just return JSON containing the version number of the service receiving the request.
The async task (asyncRequest) code is below:
public class AsyncRequest extends AsyncTask<URL, Void, List<String>> {
private String logtag = "AsyncRequestTask";
public AsyncResponse delegate;
List<String> projects = new ArrayList<String>();
#Override
protected void onPreExecute(){
super.onPreExecute();
}
#Override
protected List<String> doInBackground(URL... urls) {
try {
// Creating & connection Connection with url and required Header.
HttpURLConnection urlConnection = (HttpURLConnection) urls[0].openConnection();
urlConnection.setRequestProperty("Content-Type", "application/json");
urlConnection.setRequestMethod("GET"); //POST or GET
urlConnection.setRequestProperty("User-Agent", "Test");
// CODE HANGS HERE
int responseCode = urlConnection.getResponseCode();
String responseMessage = urlConnection.getResponseMessage();
projects.add(responseMessage);
} catch (Exception e) {
Log.e(logtag, e.toString());
}
return projects;
}
#Override
protected void onPostExecute(List<String> result){
delegate.processFinish(result);
}
}
Once I have the request working I will populate the projects variable with what I actually want to return but for now I just have it set to responseMessage. I'm sure this is just something to do with my unfamiliarity in making requests in Java, but I have spent days on this and can't figure it out. Any help is greatly appreciated.

asyncRequest.execute(url);
asyncRequest.getStatus();
String[] projects = asyncRequest.get();
It is not possible to do both an .execute and a .get().
As you should never use .get(), you better remove that statement.
Remove all code after asyncRequest.execute(url); and put that code in the onPostExecute of your AsyncTask.

Finish procedure before starting a new one

I am beginner in Android and I need some help. So, I have a procedure with sub-procedures inside. How can I finish one before starting a new one. Here is a code to better understand:
public void onCellLocationChanged(CellLocation lokacija) {
super.onCellLocationChanged(lokacija);
location = (GsmCellLocation) Phone.getCellLocation();
textCellId.setText(String.valueOf(location.getCid() % 65536));
textCellLac.setText(String.valueOf(location.getLac()));
String JSON_URL_string=JSON_URL + "?cellid=" + String.valueOf(location.getCid()%65636);
getJSON(JSON_URL_string);
myJSONString = textCellNameSakriven.getText().toString();
ParseJSON(myJSONString);
}
Problem is that myJSONString is empty, cause textCEllNameSkriven is also empty. That textView textCellNameSkriven is made when getJSON(JSON_URL_string) is finished. If I run debugger and go step by step, app goes directly from getJSON(JSON_URL_string) row to the next one and the next etc
Edit: Maybe the problem is that onPostExecute is not finished before starting ParseJSON. Here is also a code for getJSON:
private void getJSON(String url) {
class GetJSON extends AsyncTask<String, Void, String> {
ProgressDialog loading;
#Override
protected void onPreExecute() {
super.onPreExecute();
loading = ProgressDialog.show(MainActivity.this, "Please Wait...", null, true, true);
}
#Override
protected String doInBackground(String... params) {
String uri = params[0];
BufferedReader bufferedReader = null;
try {
URL url = new URL(uri);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
StringBuilder sb = new StringBuilder();
bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String json;
while ((json = bufferedReader.readLine()) != null) {
sb.append(json + "\n");
}
return sb.toString().trim();
} catch (Exception e) {
return null;
}
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
loading.dismiss();
textCellNameSakriven.setText(s);
}
}
GetJSON gj = new GetJSON();
gj.execute(url);
}

Since you are running a async task it practically runs on a different thread, so your getJson method need not wait for post execute and can return after starting the async task, so you can never be sure in this way that parseJson gets executed after textView is populated. You are running into classic race condition issue.
Your issue could be easily solved, if you have a callback which is called after postExecute is done, and you can handle parseJson there
So, something simple like , create interface MyCallback
public interface MyCallback {
public OnReadJsonDone();
}
Let your activity implement this MyCallback
public MainActivity implements MyCallback
{
...........
#Override
public OnReadJsonDone(){
parseJson();
}
Now change signature of getJson to
getJSON(string json, final MyCallback callback) {
Now in onpostexecute
//call OnReadJsonDone
callback.OnReadJsonDone()
So, all you now need is while calling getJSon pass this as second param
getJSON(JSON_URL_string,this);
Haven't tested this but you get the idea

Checking the AsyncTask status seems not working correctly (log doesn't appear on log cat)

I'm trying to see how works an Asynctask class in android. In particular i want reveal in real time the status of the class for see when it is running and when it has finished. For do this, i have created a class that extend the main activity and another class that is the asynctaks class.
This is my main class:
public class PhotoManagement extends Activity{
private String numberOfSelectedPhotos;
private Bitmap currentImage;
private String initConfiguration = "http://www.something.com";
private String response;
private ArrayList<String> formatPhotoList = new ArrayList<String>(); //create a list that will contains the available format of the photos downloaded from the server
private ArrayList<String> pricePhotoList = new ArrayList<String>(); //create a list that will contains the available price for each format of the photos
DownloadWebPageTask webPage = new DownloadWebPageTask();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
protected void onResume(){
super.onResume();
webPage.execute(initConfiguration);
if(webPage.getStatus() == AsyncTask.Status.PENDING){
Log.i("STATUS","PENDING");
}
if(webPage.getStatus() == AsyncTask.Status.RUNNING){
Log.i("","RUNNING");
}
if(webPage.getStatus() == AsyncTask.Status.FINISHED){
Log.i("","FINISHED");
}
}
}
As you can see i want only see the passages of the status with a simple log.
And here there is the asynctask class.
private class DownloadWebPageTask extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... urls) {
for (String url : urls) {
DefaultHttpClient client = new DefaultHttpClient(); //create a new http client
HttpGet httpGet = new HttpGet(url); //create a new http request passing a valid url
try {
HttpResponse execute = client.execute(httpGet); //try to execute the http get request
InputStream content = execute.getEntity().getContent(); //prepare the input stream to read the bytes of the request
BufferedReader buffer = new BufferedReader(
new InputStreamReader(content));
String s = "";
while ((s = buffer.readLine()) != null) {
response += s; //until is present a line to read, the response variable store the value of the lines
}
} catch (Exception e) {
Log.i("MyApp", "Download Exception : " + e.toString()); //Print the error if something goes wrong
}
}
return response; //return the response
}
#Override
protected void onPostExecute(String result) {
result = doInBackground(initConfiguration); //take the result from the DownloadWebPageTask class
result = result.replace("null", "");
Log.i("RESULT",""+result);
//find the price and format value from the result using XmlPullParser
try {
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
factory.setNamespaceAware(true);
XmlPullParser xpp = factory.newPullParser();
xpp.setInput( new StringReader ( result ) );
int attributeNumber = xpp.getAttributeCount();
int eventType = xpp.getEventType();
String currentTag = null;
while(eventType != XmlPullParser.END_DOCUMENT){
if(eventType == XmlPullParser.START_TAG) {
currentTag = xpp.getName();
if (currentTag.equals("product")){
xpp.getAttributeValue(null, "name");
formatPhotoList.add(xpp.getAttributeValue(null, "name"));
Log.i("FORMAT PHOTO",""+xpp.getAttributeValue(null, "name"));
}
}
eventType = xpp.next();
}
} catch (XmlPullParserException e) {
e.printStackTrace();
Log.i("","ERROR XML PULL PARSER");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
Log.i("","ERROR IOEXCEPTION");
}
}
}
}
As you can see i have implemented also the method onPostExecute that should be called when the asynctask method has finished to execute the instructions right?
So at this point i don't understand why my log RUNNING and my log FINISHED never appear on the log cat.
What i'm doing wrong?
I'm tried to follow this topic Android, AsyncTask, check status? but in my case it isn't working.
Thanks

Problem :
You are creating object like
DownloadWebPageTask webPage = new DownloadWebPageTask();
But you are calling asynctask on different object,
new DownloadWebPageTask().execute(initConfiguration);
Solution :
It should be like
webPage.execute(initConfiguration);

#Override
protected void onResume(){
super.onResume();
new DownloadWebPageTask().execute(initConfiguration);
here do like this
#Override
protected void onResume(){
super.onResume();
webPage.execute(initConfiguration);

You didn't implement webPage.execute(), add it

Most probably the task hasn't finished or even started yet. As you probably know the AsyncTask is doing it's (background) work on a different thread, so your onResume is running in parallel with it. You can either use the task's get() method to wait for it to finish and get the result of the doInBackground() method and then query for it's status or notify your activity from the task's onPostExecute() method to let it know (and log) that it has finished. I don't recommend you the first option because it will actually block the UI thread and will make your usage of AsyncTask pointless.

General AsyncTask, use one AsyncTask in multiple contexts

I'm using AsyncTask and all the examples I found about an AsyncTask is inside an activity.
I'm trying to make an application with a lot of activity and some must download a HTML page. I don't really want to copy-paste the same code all the time in every activity. I find this to be dirty.
So I need to do it as a special class Async HttpGet and pass the function with an argument. I will execute after the doinbackground (different for every activity).
Is this possible or do I need to copy-paste my code in every activity and change the do in background to do what I need after downloading the HTML page?

Here's an AsyncTask that will download data from a url and update the calling activity.
Make sure your calling activity implements the interface DownloadDataTask.DownloadCompleteHandler and that it passes itself as parameter to the DownloadDataTask constructor.
public class DownloadDataTask extends AsyncTask<String, Integer, String> {
public interface DownloadCompleteHandler
{
public void handleDownloadComplete(String result);
}
private DownloadCompleteHandler handler;
private String url;
public DownloadDataTask(DownloadCompleteHandler handler, String url) {
this.handler = handler;
this.url = url;
}
/* AsyncTask methods */
#Override
protected String[] doInBackground(String... empty) {
return downloadData(url);
}
#Override
protected void onPostExecute(String result) {
handler.handleDownloadComplete(result);
}
/* Downloading Data */
private String downloadData(String urlStr) {
InputStream is = null;
String result = new String();
try {
is = getInputStream(urlStr);
BufferedReader in = new BufferedReader(new InputStreamReader(is));
String inputLine;
while ((inputLine = in.readLine()) != null) {
result += inputLine;
} catch (MalformedURLException ex) {
return "Malformed URL: " + ex.getMessage();
} catch (SocketTimeoutException ex) {
return "Connection timed out";
} catch (IOException ex) {
return "IOException: " + ex.getMessage();
}
finally {
if (is != null)
is.close();
}
return result;
}
private InputStream getInputStream(String urlStr) throws IOException
{
URL url = new URL(urlStr);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(7000);
conn.setConnectTimeout(7000);
conn.setRequestMethod("GET");
conn.setDoInput(true);
conn.connect();
return conn.getInputStream();
}
}

Just create a class that extends AsyncTask that you can reuse.
public abstract class MyAsyncTask extends AsyncTask<Void, Void, String> {
private final String url;
public MyAsyncTask(String url){
this.url = url;
}
#Override
protected String doInBackground(Void... params){
// get data from url.
return null;
}
}
And then to call it, just create an instance of that class.
new MyAsyncTask("http://www.google.com"){
public void onPostExecute(String result){
// update your views.
}
}.execute();

Well what you can do is create an listener for AsyncTask completion, which listens when your AsyncTask is completed and return you the data. I had created an example to execute database queries in background thread and then returning the data to the Activity. Just check it and you can create similar AsyncTask for your problem.
UPDATE:-
Also you can use BroadCastReceiver as a Listener when your AsyncTask is completed and return the value.
Interface is another option for creating a Listener for AsyncTask.
Here is a demo from my github