Develop Reference

Calling AsyncTask class it does not execute doInBackgound method

when calling
new AsyncFeed(strurl).execute();
after this its able to call constructor of AsyncFeed but not able to execute doInBackground(). while debugging i found out it calls constructor and then simply returns back to the calling statement making a nullpointer exception in later code
public class HttpHandler {
public HttpHandler() {
}
URL url;
HttpURLConnection httpURLConnection = null;
InputStream inputStream;
BufferedReader bufferedReader = null;
StringBuffer stringBuffer;
String strurl;
public String getJsonString(String strurl){
new AsyncFeed(strurl).execute();
return String.valueOf(stringBuffer);
}
class AsyncFeed extends AsyncTask<String,Void,String>{
String urlStr;
public AsyncFeed(String urlStr) {
this.urlStr=urlStr;
}
#Override
protected String doInBackground(String... strings) {
try {
url = new URL(urlStr);
httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.connect();
inputStream = httpURLConnection.getInputStream();
bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String line;
stringBuffer = new StringBuffer();
while ((line=bufferedReader.readLine()) != null){
stringBuffer.append(line);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(bufferedReader !=null)
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
httpURLConnection.disconnect();
}
return null;
}

If you think that stringBuffer is null, it's because function public String getJsonString(String strurl) returns String value of uninitialized stringBuffer before AsyncFeed is completed. You should use something like this:
public void loadJsonString(String strurl){
new AsyncFeed(strurl).execute();
//return String.valueOf(stringBuffer);
}
class AsyncFeed extends AsyncTask<Void,Void,Void>{
String urlStr;
public AsyncFeed(String urlStr) {
this.urlStr=urlStr;
}
#Override
protected String doInBackground(Void... records) {
try {
url = new URL(urlStr);
httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.connect();
inputStream = httpURLConnection.getInputStream();
bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String line;
stringBuffer = new StringBuffer();
while ((line=bufferedReader.readLine()) != null){
stringBuffer.append(line);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(bufferedReader !=null)
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
httpURLConnection.disconnect();
}
return null;
}
#Override
protected void onPreExecute() {
//f.e. show progress dialog
}
#Override
protected void onPostExecute(Void result) {
//now you have initialized stringBuffer so do what you want with it
//hide progress dialog
//print String value of stringBuffer initialized in doInBackground
System.out.print(String.valueOf(stringBuffer));
}
)
There are more options to do that but it's hard to write exactly what you need without seeing more of your code or specify your question, so if you have some
questions to me just write comment :) or read more here Android Developers - AsyncTask
EDIT
Okay I understand, try do it like this, the idea is just pass calling object into the async task and from there in onPostExecute() will be updated data
in ClassA and continue with what you need
public class ClassA{
String url;
String jsonObjectString;
//instead of getJsonString(url) call this and after async task will finish
//it calls updateDataFromAsync() so you will have data loaded and you can continue work with it in doSomethingAfterAsync()
private void loadData(){
//pass the calling object into the async task
new HttpHandler(this).startLoadJsonString(url);
}
//this will async taks call in onPostExecute()
public void updateDataFromAsync(String s){
jsonObjectString = s;
doSomethingAfterAsync();
}
private doSomethingAfterAsync(){
}
}
public class HttpHandler {
URL url;
HttpURLConnection httpURLConnection = null;
InputStream inputStream;
BufferedReader bufferedReader = null;
StringBuffer stringBuffer;
String strurl;
ClassA classA;
public HttpHandler(ClassA classA) {
this.classA = classA;
}
public void startLoadJsonString(String strurl){
new AsyncFeed(strurl).execute();
}
private class AsyncFeed extends AsyncTask<Void,Void,Void>{
String urlStr;
public AsyncFeed(String urlStr) {
this.urlStr=urlStr;
}
#Override
protected String doInBackground(Void... records) {
try {
url = new URL(urlStr);
httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.connect();
inputStream = httpURLConnection.getInputStream();
bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String line;
stringBuffer = new StringBuffer();
while ((line=bufferedReader.readLine()) != null){
stringBuffer.append(line);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(bufferedReader !=null)
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
httpURLConnection.disconnect();
}
return null;
}
#Override
protected void onPreExecute() {
//f.e. show progress dialog
}
#Override
protected void onPostExecute(Void result) {
//now you have initialized stringBuffer so do what you want with it
//hide progress dialog
//call updateDataFromAsync from ClassA class and continue there
classA.updateDataFromAsync(String.valueOf(stringBuffer));
}
)

Android HttpUrlConnection Url doesn't work on emulator

I am trying to get json object as string from this url http://digitalcollections.tcd.ie/home/getMeta.php?pid=MS4418_021. It doesn't work I get an error after downloadUrl function.
java.io.IOException: unexpected end of stream on Connection{digitalcollections.tcd.ie:80, proxy=DIRECT# hostAddress=134.226.115.12 cipherSuite=none protocol=http/1.1} (recycle count=0)
Although it does work for this androidhive url http://api.androidhive.info/volley/person_object.json.
I am new to httpconnection below is my download url function. Error seems to show in this line HttpURLConnection conn = (HttpURLConnection) url.openConnection(); In the debugger after that line conn.getInputStream() shows the IO exception and the cause java.io.EOFException: \n not found: size=0 content=...
// Given a string representation of a URL, sets up a connection and gets
// an input stream.
private InputStream downloadUrl(String urlString) throws IOException {
URL url = new URL(urlString);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(20000 /* milliseconds */);
conn.setConnectTimeout(30000 /* milliseconds */);
conn.setRequestMethod("GET");
//conn.setDoInput(true);
// Starts the query
conn.connect();
InputStream stream = conn.getInputStream();
return stream;
}
Other functions.
// Uses AsyncTask to create a task away from the main UI thread. This task takes a
// URL string and uses it to create an HttpUrlConnection. Once the connection
// has been established, the AsyncTask downloads the contents of the webpage as
// an InputStream. Finally, the InputStream is converted into a string, which is
// displayed in the UI by the AsyncTask's onPostExecute method.
private class DownloadXMLTask extends AsyncTask<String, Void, List<Entry>> {
private String urlFront = "";
#Override
protected List<Entry> doInBackground(String... urls) {
// params comes from the execute() call: params[0] is the url.
try {
return loadJsonFromNetwork(urls[0]);
} catch (IOException e) {
Log.d(TAG, "Unable to retrieve web page. URL may be invalid.");
return null;
} catch (JSONException e) {
Log.d(TAG, "XMLPULLPARSER ERROR IN download json task function");
return null;
}
}
}
// onPostExecute displays the results of the AsyncTask.
#Override
protected void onPostExecute(List<Entry> result) {
//post execution stuff
}
}
Loading json and parser, the parser might not work haven't tested it yet.
private List<Entry> loadJsonFromNetwork(String urlString) throws IOException, JSONException {
InputStream stream = null;
int len = 20000; //max amount of characters to display in string
List<Entry> entries = new ArrayList<Entry>();
try {
stream = downloadUrl(urlString); //IOException
String jsonStr = readit(stream,len);
if(jsonStr.equals(null)){
Log.d(TAG, "ERROR json string returned null");
return entries;
}
JSONObject jsonObj = new JSONObject(jsonStr);
//Not sure if the json parser works yet haven't got that far
// Getting JSON Array node
identifier = jsonObj.getJSONArray("identifier");
// looping through All Contacts
for (int i = 0; i < identifier.length(); i++) {
JSONObject c = identifier.getJSONObject(i);
String id = c.getString("type");
if(id.equals("DRIS_FOLDER")) {
String folder = c.getString("$");
entries.add(new Entry(null,null,null,folder));
}
}
// Makes sure that the InputStream is closed after the app is
// finished using it.
//This is where IOexception is called and stream is null
} catch (IOException e) {
Log.d(TAG, "Unable to retrieve json web page. URL may be invalid."+ e.toString());
return entries;
}
finally {
if (stream != null) {
stream.close();
}
}
return entries;
}
I am running this on a Nexus_5_API_23 emulator.
Thanks in advance.
UPDATE:
Doesn't work on Nexus_5_API_23 emulator?? Although it works on a Samsung GT-ST7500 external phone. Want it to work for the emulator.

The problem was my antivirus/firewall on my computer. It was blocking my connection and that's why it was working on a external phone and not emulator. I disabled my antivirus/firewall and it worked. There is a list of network limitations here http://developer.android.com/tools/devices/emulator.html#networkinglimitations

I just tried that URL on my device and didn't get any errors. Here is the code I used.
An Interface to get back onto the UI Thread
public interface AsyncResponse<T> {
void onResponse(T response);
}
A generic AsyncTask that returns a String - Feel free to modify this to parse your JSON and return a List.
public class WebDownloadTask extends AsyncTask<String, Void, String> {
private AsyncResponse<String> callback;
public void setCallback(AsyncResponse<String> callback) {
this.callback = callback;
}
#Override
protected String doInBackground(String... params) {
String url = params[0];
return readFromUrl(url);
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
if (callback != null) {
callback.onResponse(s);
} else {
Log.w(WebDownloadTask.class.getSimpleName(), "The response was ignored");
}
}
private String streamToString(InputStream is) throws IOException {
StringBuilder sb = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
String line;
while ((line = rd.readLine()) != null) {
sb.append(line);
}
return sb.toString();
}
private String readFromUrl(String myWebpage) {
String response = null;
HttpURLConnection urlConnection = null;
try {
URL url = new URL(myWebpage);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = urlConnection.getInputStream();
if (inputStream != null) {
response = streamToString(inputStream);
inputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
}
return response;
}
}
Section of my Activity to call the AsyncTask.
String url = "http://digitalcollections.tcd.ie/home/getMeta.php?pid=MS4418_021";
WebDownloadTask task = new WebDownloadTask();
task.setCallback(new AsyncResponse<String>() {
#Override
public void onResponse(String response) {
Toast.makeText(getApplicationContext(), response, Toast.LENGTH_SHORT).show();
}
});
task.execute(url);

Make sure to use https instead of http to avoid these kind of errors on your Android Emulators.
private static final String BASE_URL = "https://content.guardianapis.com/search?";

Using Android DownloadManager,how do i get file name?

I'm using DownloadManager class to manage downloads, i'm using this
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS,subPath);
currently i'm setting subPath to some filename but how do i get filename from url?
I don't want to use cursor but some way to extract file name from uri.

You can use:
DownloadManager.COLUMN_TITLE
Please look at Android DownloadManager get filename
Hope this helps!

Well , if no cursor then try this:
class GetFileName extends AsyncTask<String, Integer, String>
{
protected String doInBackground(String... urls)
{
URL url;
String filename = null;
try {
url = new URL(urls[0]);
String cookie = CookieManager.getInstance().getCookie(urls[0]);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setRequestProperty("Cookie", cookie);
con.setRequestMethod("HEAD");
con.setInstanceFollowRedirects(false);
con.connect();
String content = con.getHeaderField("Content-Disposition");
String contentSplit[] = content.split("filename=");
filename = contentSplit[1].replace("filename=", "").replace("\"", "").trim();
} catch (MalformedURLException e1) {
e1.printStackTrace();
} catch (IOException e) {
}
return filename;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected void onPostExecute(String result) {
}
}

d How can I use progress bar while fetching data from database?

I'm really bad at googling things I want so I decided to ask here. My question is is it possible to show a progress bar while fetching the data from the database? I'm using the typical code when fetching data(Pass value to php and the php will do the query and pass it again to android)
Edit(I have tried adding proggressdialog but the problem now is the loaded data will appear first before the progress dialog here's my AsyncTask code)
public class getClass extends AsyncTask<String, Void, String> {
public getClass()
{
pDialog = new ProgressDialog(getActivity());
}
URLConnection connection = null;
String command;
Context context;
String ip = new returnIP().getIpAddresss();
String link = "http://" + ip + "/android/getClass.php";//ip address/localhost
public URLConnection getConnection(String link) {
URL url = null;
try//retrieves link from string
{
url = new URL(link);
} catch (MalformedURLException e) {
e.printStackTrace();
}
URLConnection connection = null;
try//opens the url link provided from the "link" variable
{
connection = url.openConnection();
} catch (IOException e) {
e.printStackTrace();
}
connection.setDoOutput(true);
return connection;
}
public String getResult(URLConnection connection, String logs) {
//this is the functions that retrieves what the php file echoes
//everything that php throws, the phone receives
String result = "";
OutputStreamWriter wr = null;
try {
wr = new OutputStreamWriter(connection.getOutputStream());//compiles data to be sent to the receiver
} catch (IOException e) {
e.printStackTrace();
}
try {
wr.write(logs);
} catch (IOException e) {
e.printStackTrace();
}
try {
wr.flush();//clears the cache-esque thingy of the writer
} catch (IOException e) {
e.printStackTrace();
}
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
} catch (IOException e) {
e.printStackTrace();
}
StringBuilder sb = new StringBuilder();
String line = null;
//Read server response
try {
while ((line = reader.readLine()) != null) {
sb.append(line);
}
} catch (IOException e) {
e.printStackTrace();
}
result = sb.toString();
return result;
}
#Override
protected void onPreExecute() {
pDialog.setMessage("Loading...");
pDialog.show();
}
#Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub
String result = "";
//Toast.makeText(View_Classes.this, "ako n una", Toast.LENGTH_LONG).show();
try {
//first data sent is sent in command
command = (String) arg0[0];//it's in array, because everything you input here is placed in arrays
//Toast.makeText(View_Classes.this, "andtio n me", Toast.LENGTH_LONG).show();
if (command == "getCourses") {
connection = getConnection(link);
String logs = "";
logs = "&command=" + URLEncoder.encode(command, "UTF-8");
logs += "&username=" + URLEncoder.encode(username, "UTF-8");
result = getResult(connection, logs);
} else if (command == "getSections") {
connection = getConnection(link);
String logs = "";
logs = "&command=" + URLEncoder.encode(command, "UTF-8");
logs += "&username=" + URLEncoder.encode(username, "UTF-8");
logs += "&course=" + URLEncoder.encode(course, "UTF-8");
result = getResult(connection, logs);
}
return result;
} catch (Exception e) {
return result;
}
}
#Override
protected void onPostExecute(String result) {//this is going to be the next function to be done after the doInBackground function
// TODO Auto-generated method stub
if (pDialog.isShowing()) {
pDialog.dismiss();
}
if (result.equalsIgnoreCase(""))//if there's nothing to return, the text "No records" are going to be thrown
{
} else //Array adapter is needed, to be a place holder of values before passing to spinner
{
}
}
}

Have you tried using an AsyncTask?
You can show your progress bar on the preExecute method and then hide it on postExecute. You can do your querying inside the doInBackground method.

In addition to what #torque203 pointed, I would suggest you to check
http://developer.android.com/reference/android/os/AsyncTask.html#onProgressUpdate(Progress...)
this method was created for that purpose, showing progress to the user.

From developers docs:
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
#Override
protected void onPreExecute() {
//show progress bar here
}
protected Long doInBackground(URL... urls) {
//Pass value to PHP here
//get values from your PHP
}
protected void onPostExecute(Long result) {
//Here you are ready with your PHP value. Dismiss progress bar here.
}
}

public void onPreExecute() {
Progress Dialog pDialog = new ProgressDialog(this);
pDialog.setMessage("Loading...");
pDialog.show();
}
public void doInBackground() {
//do your JSON Coding
}
public void onPostExecute() {
Progress Dialog pDialog = new ProgressDialog(this);
pDialog.setMessage("Loading...");
pDialog.show();
}

public URLConnection getConnection(String link) {
URL url = null;
try//retrieves link from string
{
url = new URL(link);
} catch (MalformedURLException e) {
e.printStackTrace();
}
URLConnection connection = null;
try//opens the url link provided from the "link" variable
{
connection = url.openConnection();
} catch (IOException e) {
e.printStackTrace();
}
connection.setDoOutput(true);
return connection;
}
public String getResult(URLConnection connection, String logs) {
//this is the functions that retrieves what the php file echoes
//everything that php throws, the phone receives
String result = "";
OutputStreamWriter wr = null;
try {
wr = new OutputStreamWriter(connection.getOutputStream());//compiles data to be sent to the receiver
} catch (IOException e) {
e.printStackTrace();
}
try {
wr.write(logs);
} catch (IOException e) {
e.printStackTrace();
}
try {
wr.flush();//clears the cache-esque thingy of the writer
} catch (IOException e) {
e.printStackTrace();
}
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
} catch (IOException e) {
e.printStackTrace();
}
StringBuilder sb = new StringBuilder();
String line = null;
//Read server response
try {
while ((line = reader.readLine()) != null) {
sb.append(line);
}
} catch (IOException e) {
e.printStackTrace();
}
result = sb.toString();
return result;
}
public class getClass extends AsyncTask<String, Void, String> {
#Override
protected void onPreExecute() {
pDialog.setMessage("Loading...");
pDialog.show();
URLConnection connection = null;
String command;
Context context;
String ip = new returnIP().getIpAddresss();
String link = "http://" + ip + "/android/getClass.php";//ip address/localhost
}
#Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub
String result = "";
//Toast.makeText(View_Classes.this, "ako n una", Toast.LENGTH_LONG).show();
try {
//first data sent is sent in command
command = (String) arg0[0];//it's in array, because everything you input here is placed in arrays
//Toast.makeText(View_Classes.this, "andtio n me", Toast.LENGTH_LONG).show();
if (command == "getCourses") {
connection = getConnection(link);
String logs = "";
logs = "&command=" + URLEncoder.encode(command, "UTF-8");
logs += "&username=" + URLEncoder.encode(username, "UTF-8");
result = getResult(connection, logs);
} else if (command == "getSections") {
connection = getConnection(link);
String logs = "";
logs = "&command=" + URLEncoder.encode(command, "UTF-8");
logs += "&username=" + URLEncoder.encode(username, "UTF-8");
logs += "&course=" + URLEncoder.encode(course, "UTF-8");
result = getResult(connection, logs);
}
return result;
} catch (Exception e) {
return result;
}
}
#Override
protected void onPostExecute(String result) {//this is going to be the next function to be done after the doInBackground function
// TODO Auto-generated method stub
if (pDialog.isShowing()) {
pDialog.dismiss();
}
if (result.equalsIgnoreCase(""))//if there's nothing to return, the text "No records" are going to be thrown
{
} else //Array adapter is needed, to be a place holder of values before passing to spinner
{
}
}
}

URL validation works fine but keep connection and restrict any further requests

public class UrlVarificationTask extends AsyncTask<Void, Void, Integer> {
private String url;
private UrlVarificationDelegate delegate;
private HttpURLConnection huc;
public UrlVarificationTask(String url, UrlVarificationDelegate delegate) {
this.url = url;
this.delegate = delegate;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected Integer doInBackground(Void... params) {
int responseCode = 0;
try {
System.setProperty("http.keepAlive", "false");
URL u = new URL(url);
huc = (HttpURLConnection) u.openConnection();
huc.setRequestMethod("HEAD");
huc.connect();
responseCode = huc.getResponseCode();
} catch (MalformedURLException mal) {
responseCode = -555;
} catch (IOException io) {
responseCode = -444;
} catch (Exception ex) {
responseCode = -333;
ex.printStackTrace();
}
if (huc != null) {
try {
huc.getInputStream().close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
huc.disconnect();
}
Logger.debug("Response Code==" + responseCode);
return responseCode;
}
#Override
protected void onPostExecute(Integer responseCode) {
delegate.urlVarificationResponseCode(responseCode);
super.onPostExecute(responseCode);
}
}
I used above dode for validating url,
if HEAD give me response code 200 then only I open a url to webview.
but once I call this it keep connection and not allow any other http request even after close, what to do ?
Safe use of HttpURLConnection

huc.setRequestProperty("keep-alive", "false");
this is working as HttpURLConnection keep connection alive and hence we cann't make make further request so keep-alive setting to false resolve this problem.

For properly closing the HttpURLConnection go to the link
By this URL is closed.