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.
Related
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.
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.
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?";
I wanna get some data from server with this code :
public class Webservice {
public static String readUrl(String url, ArrayList<NameValuePair> params) {
try {
HttpClient client = new DefaultHttpClient();
HttpPost method = new HttpPost(url);
if (params != null) {
method.setEntity(new UrlEncodedFormEntity(params));
}
HttpResponse response = client.execute(method);
InputStream inputStream = response.getEntity().getContent();
String result = convertInputStreamToString(inputStream);
return result;
}
catch (ClientProtocolException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
return null;
}
private static String convertInputStreamToString(InputStream inputStream) {
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder builder = new StringBuilder();
String line = "";
while ((line = reader.readLine()) != null) {
builder.append(line);
}
return builder.toString();
}
catch (IOException e) {
e.printStackTrace();
}
return null;
}
}
but there is some delay and pause in the application , so i wanna run this code in the Thread , but when i tried to do it , i got some error , for example i couldn't return the result or ...
Take a look at AsyncTask:
Network operations can involve unpredictable delays. To prevent this
from causing a poor user experience, always perform network operations
on a separate thread from the UI. The AsyncTask class provides one of
the simplest ways to fire off a new task from the UI thread. For more
discussion of this topic, see the blog post Multithreading For
Performance.
In the following snippet, the myClickHandler() method invokes new
DownloadWebpageTask().execute(stringUrl). The DownloadWebpageTask
class is a subclass of AsyncTask.
public class HttpExampleActivity extends Activity {
private static final String DEBUG_TAG = "HttpExample";
private EditText urlText;
private TextView textView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
urlText = (EditText) findViewById(R.id.myUrl);
textView = (TextView) findViewById(R.id.myText);
}
// When user clicks button, calls AsyncTask.
// Before attempting to fetch the URL, makes sure that there is a network connection.
public void myClickHandler(View view) {
// Gets the URL from the UI's text field.
String stringUrl = urlText.getText().toString();
ConnectivityManager connMgr = (ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
new DownloadWebpageTask().execute(stringUrl);
} else {
textView.setText("No network connection available.");
}
}
// 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 DownloadWebpageTask extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... urls) {
// params comes from the execute() call: params[0] is the url.
try {
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve web page. URL may be invalid.";
}
}
// onPostExecute displays the results of the AsyncTask.
#Override
protected void onPostExecute(String result) {
textView.setText(result);
}
}
... }
I have a text file on a server (right now on a local server by WAMP in c:/wamp/www/android/sample.txt ) and an android application with 3 activity that read data through the WiFi.
The first one get the address (on local host use 10.0.2.2/android/sample.txt) and go to activity2. In activity2 I have a button that goes to activity3.
code is third activity:
private InputStream OpenHttpConnection(String urlString) throws Exception {
InputStream in = null;
int response = -1;
URL url = new URL(urlString);
URLConnection conn = url.openConnection();
if (!(conn instanceof HttpURLConnection)) {
throw new IOException("NOT an HTTP Connection!");
}
try {
HttpURLConnection httpCon = (HttpURLConnection) conn;
httpCon.setAllowUserInteraction(false);
httpCon.setInstanceFollowRedirects(true);
httpCon.setRequestMethod("GET");
httpCon.connect();
response = httpCon.getResponseCode();
if (response == HttpURLConnection.HTTP_OK) {
in = httpCon.getInputStream();
Log.d("myerr", response + "");
}
} catch (Exception e) {
Log.d("myerr2", e.getLocalizedMessage());
throw new IOException("Error Connection!");
}
return in;
}
private String DownloadText(String URL) {
int BUFFER_SIZE = 2000;
InputStream in = null;
try {
in = OpenHttpConnection(URL);
} catch (Exception e) {
Log.d("myerr", e.getLocalizedMessage());
return "";
}
InputStreamReader isr = new InputStreamReader(in);
int charRead;
String str = "";
char[] inputBuffer = new char[BUFFER_SIZE];
try {
while ((charRead = isr.read(inputBuffer)) > 0) {
String readString = String
.copyValueOf(inputBuffer, 0, charRead);
str += readString;
inputBuffer = new char[BUFFER_SIZE];
}
in.close();
} catch (Exception e) {
Log.d("myerr", e.getLocalizedMessage());
return "";
}
return str;
}
private class DownloadTextTask extends AsyncTask<String, Void, String> {
protected String doInBackground(String... urls) {
return DownloadText(urls[0]);
}
protected void onPostExecute(String result) {
Global.readedDataFromFile=result;
//Toast.makeText(DrawRhActivity.this,"Result: "+Global.readedDataFromFile, Toast.LENGTH_LONG).show();
}
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_draw_rh);
String user_address = Global.ip_address;
new DownloadTextTask().execute(user_address);
tv = (TextView) findViewById(R.id.textView1);
tv.setText("Value: " + Global.readedDataFromFile);
}
I also define some global variable in Global.java .
AND HERE IS MY PROBLEM:
The 3rd activity doesn't show data on textview at the first time. but when I back to 2nd activity and hit the button my data loaded.
Why AsyncTask doesn't show result first time and how to fix this?
Thanks for your attention.
tv.setText("Value: " + Global.readedDataFromFile);
write this line in onPostExecute
protected void onPostExecute(String result) {
Global.readedDataFromFile=result;
//Toast.makeText(DrawRhActivity.this,"Result: "+Global.readedDataFromFile, Toast.LENGTH_LONG).show();
tv.setText("Value: " + Global.readedDataFromFile);
}
Solution:
put tv.setText("Value: " + Global.readedDataFromFile); in your onPostExecute method.
Explaination:
AsyncTask runs on separate thread instead of your UI thread.
so when it is being executed Global.readedDataFromFile may be empty.and when execution completes it goes in onPostExecute method and now Global.readedDataFromFile have some value stored in it.
Issue:
you are setting the text instantly after calling new DownloadTextTask().execute(user_address);
so it may happen that the AsyncTask is not completed yet and Global.readedDataFromFile is empty.
Reference:
AsyncTask
I hope it will be helpful !!
the problem lies within your onCreate function:
String user_address = Global.ip_address;
new DownloadTextTask().execute(user_address);
tv = (TextView) findViewById(R.id.textView1);
tv.setText("Value: " + Global.readedDataFromFile);
First you start a task, then you want to set your views, but your task is not finished.
You have to set the views with the result of your task in to onPostExecute of the task.
Keep your DownloadTextTask &
Trying this code in your Activity
DownloadTextTask textTask = new DownloadTextTask();
textTask.execute(user_address);
String strDownloaded = "";
try {
strDownloaded = textTask.get();
} catch (Exception e) {
Log.e("DownloadTextTask", "Error: " + e.getMessage());
}