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));
}
)
Related
I try to create synchronized threads, but I always get the following error: android.os.NetworkOnMainThreadException.
I've read more posts, but they don't work for me.
Below I write the code blocks that do not work for me:
1.
final SyncApp syncJob = new SyncApp();
Thread t = new Thread (new Runnable () {
#Override
public void run () {
synchronized (syncJob) {
String s = syncJob.insert (newJobs, GlobalVariables.URL_LOCALHOST + "jobs");
txtState.setText (s);
}}});
}
});
t.Start ();
// t.run ();
2.
myClass.runOnUiThread(new Runnable() {
public void run() {...}
})
3.
Running code in main thread from another thread
SyncApp:
public class SyncApp {
synchronized public String insert(List<Jobs> job, String... params) {
URL url = null;
HttpURLConnection conn = null;
try {
url = new URL(params[0]);
conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setRequestProperty("Content-Type", "application/json");
conn.setDoInput(true);
conn.setDoOutput(true);
String str = new Gson().toJson(job);
byte[] outputInBytes = str.getBytes();
OutputStream os = conn.getOutputStream();
os.write( outputInBytes );
os.flush();
int responseCode=conn.getResponseCode();
String response = null;
if (responseCode == HttpsURLConnection.HTTP_OK) {
String line;
BufferedReader br=new BufferedReader(new InputStreamReader(conn.getInputStream()));
while ((line=br.readLine()) != null) {
response+=line;
}
}
else {
response=conn.getResponseMessage();
}
return response;
} catch (Exception e) {
e.printStackTrace();
} finally {
conn.disconnect();
}
return null;
}
}
I need to call a thread, wait for the answer and call another thread. Their answers I must use them in the activity
I need to call a thread, wait for the answer and call another thread.
Their answers I must use them in the activity
Example using async tasks to accomplish objective.
In this code, let A be your activity which needs to call a thread,
wait for the answer and call another thread. Customize as needed.
Since you never wait in UI threads, callbacks are used to accomplish synchronization.
Let A be your activity class:
public class A extends Activity {
// some method in activity where you launch a background thread (B)
// which then completes and invokes callback which then creates and launches
// a background thread (C) which then completes and invokes a callback.
//
// In callback C, you are on the UI thread.
protected void someMethod() {
new B(new B.CallbackB() {
public void result(Object o) {
new C(new C.CallbackC() {
public void result(Object o, Object answerFromB) {
// OK - C is now done and we are on UI thread!
// 'o' is answer from C
// 'answerFromB' also provided
}
}, o).execute(new Object());
}
).execute(new Object());
}
}
Define a class B:
public class B extends AsyncTask<Object, Void, Object> {
public static interface CallbackB {
void result(Object o);
}
private CallbackB cb;
public B (CallbackB cb) {
this.cb = cb;
}
protected Object doInBackground(Object... params) {
// do work and return an answer.
return new Object();
}
protected void onPostExecute(Object result) {
if (cb != null) {
cb.result(result);
}
}
}
Define a class C:
public class C extends AsyncTask<Object, Void, Object> {
public static interface CallbackC {
void result(Object o, Object answerFromB);
}
private CallbackC cb;
private Object answerFromB;
public C (CallbackC cb, Object answerFromB) {
this.cb = cb;
this.answerFromB = answerFromB;
}
protected Object doInBackground(Object... params) {
// do work and return an answer.
return new Object();
}
protected void onPostExecute(Object result) {
if (cb != null) {
cb.result(result, answerFromB);
}
}
}
For reference:
https://stackoverflow.com/a/9963705/2711811
My solution is:
public class Sync extends AppCompatActivity {
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sync_server);
dao = new DAO(this);
txtState = findViewById(R.id.txt_log);
btnSincro = findViewById(R.id.btn_sincro);
btnSincro.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
countCall = 0;
callFlow();
}
});
btnHome = findViewById(R.id.btn_home);
btnHome.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(SyncServerActivity.this, MainActivity.class);
startActivity(intent);
}
});
}
private void callFlow() {
switch (countCall) {
case 0:
templates = toTemplate("url");
break;
case 1:
jobs = toJobs("url");
break;
case 2:
job = ... //select item
res = sendJobs(jobs, "url");
break;
default:
runOnUiThread(new Runnable() {
#Override
public void run() {
btnSincro.setEnabled(true);
txtState.append("\n\nEND");
}
});
}
}
private void nextStep() {
setText(txtState, "\nSync \n" + countCall + "/3");
countCall++;
callFlow();
}
private void setText(final TextView text, final String value) {
runOnUiThread(new Runnable() {
#Override
public void run() {
text.setText(value);
}
});
}
public List<Templates> toTemplate(final String... params) {
final List<Templates> list = new ArrayList<>();
Thread t = new Thread(new Runnable() {
#Override
public void run() {
URL url = null;
BufferedReader reader = null;
HttpURLConnection connection = null;
try {
url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
int responseCode = connection.getResponseCode();
String response = null;
if (responseCode == HttpsURLConnection.HTTP_OK) {
StringBuffer buffer = new StringBuffer();
String line = "";
while ((line = reader.readLine()) != null) {
buffer.append(line);
}
String finalJson = buffer.toString();
JSONObject parentObject = new JSONObject(finalJson);
JSONArray parentArray = parentObject.getJSONArray("data");
for (int i = 0; i < parentArray.length(); i++) {
Templates item = new Gson().fromJson(parentArray.get(i).toString(), Templates.class);
list.add(item);
}
} else {
response = connection.getResponseMessage();
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
} finally {
if (connection != null)
connection.disconnect();
try {
if (reader != null)
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
nextStep(); //call next Thread
}
}
});
t.start();
return list;
}
public List<Jobs> toJobs(final String... params) {
final List<Jobs> list = new ArrayList<>();
Thread t = new Thread(new Runnable() {
#Override
public void run() {
URL url = null;
BufferedReader reader = null;
HttpURLConnection connection = null;
try {
url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
int responseCode = connection.getResponseCode();
String response = null;
if (responseCode == HttpsURLConnection.HTTP_OK) {
StringBuffer buffer = new StringBuffer();
String line = "";
while ((line = reader.readLine()) != null) {
buffer.append(line);
}
String finalJson = buffer.toString();
JSONObject parentObject = new JSONObject(finalJson);
JSONArray parentArray = parentObject.getJSONArray("data");
for (int i = 0; i < parentArray.length(); i++) {
Jobs item = new Gson().fromJson(parentArray.get(i).toString(), Jobs.class);
list.add(item);
}
} else {
response = connection.getResponseMessage();
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
} finally {
if (connection != null)
connection.disconnect();
try {
if (reader != null)
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
nextStep();
}
}
});
t.start();
return list;
}
public Boolean sendJobs(final List<Jobs> job, final String... params) {
final Boolean[] result = {false};
Thread t = new Thread(new Runnable() {
#Override
public void run() {
URL url = null;
HttpURLConnection conn = null;
try {
url = new URL(params[0]);
conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setRequestProperty("Content-Type", "application/json");
conn.setDoInput(true);
conn.setDoOutput(true);
String str = new Gson().toJson(job);
Log.d(TAG, str);
byte[] outputInBytes = str.getBytes();
OutputStream os = conn.getOutputStream();
os.write(outputInBytes);
os.flush();
int responseCode = conn.getResponseCode();
String response = null;
if (responseCode == HttpsURLConnection.HTTP_OK) {
String line;
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
while ((line = br.readLine()) != null) {
response += line;
}
result[0] = true;
} else {
response = conn.getResponseMessage();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
conn.disconnect();
nextStep();
}
}
});
t.start();
return result[0];
}
}
Whenever a thread ends, it calls the nextStep() method, which starts the next trhead.
I have a problem with parsing a tag inside a Json object.
My json code is structured like that:
{"giocatori":[{"nome":"Giovanni","cognome":"Muchacha","numero":"1","ruolo":"F-G"},
{"nome":"Giorgio","cognome":"Rossi","numero":"2","ruolo":"AG"},
{"nome":"Andrea","cognome":"Suagoloso","numero":"3","ruolo":"P"},
{"nome":"Salvatore","cognome":"Aranzulla","numero":"4","ruolo":"G"},
{"nome":"Giulio","cognome":"Muchacha","numero":"5","ruolo":"F"}]}
I got the code that let me get the Json file from here: Get JSON Data from URL Using Android? and I'm trying to parse a tag (for example the "nome" tag) into a Json object.
This is the code I got:
public class MainActivity extends AppCompatActivity {
Button btnHit;
TextView txtJson;
ProgressDialog pd;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnHit = (Button) findViewById(R.id.btnHit);
txtJson = (TextView) findViewById(R.id.tvJsonItem);
btnHit.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
new JsonTask().execute("https://api.myjson.com/bins/177dpo");
}
});
}
private class JsonTask extends AsyncTask<String, String, String> {
protected void onPreExecute() {
super.onPreExecute();
pd = new ProgressDialog(MainActivity.this);
pd.setMessage("Please wait");
pd.setCancelable(false);
pd.show();
}
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");
Log.d("Response: ", "> " + line);
}
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 null;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
if (pd.isShowing()){
pd.dismiss();
}
txtJson.setText(result);
}
}
}
I've never worked with this type of file so I'll really appreciate your help!
You can use something like this:
try {
String servResponse = response.toString();
JSONObject parentObj = new JSONObject(servResponse);
JSONArray parentArray = parentObj.getJSONArray("giocatori");
if (parentArray.length() == 0) {
//if it's empty, do something (or not)
} else {
//Here, finalObj will have your jsonObject
JSONObject finalObj = parentArray.getJSONObject(0);
//if you decide to store some value of the object, you can do like this (i've created a nomeGiocatori for example)
nomeGiocatori = finalObj.getString("nome");
}
} catch (Exception e) {
Log.d("Exception: ", "UnknownException");
}
I use this kind of code all the time, works like a charm.
its my json file
{"VisitorsList":[{"VisitorID":"09005451","VisitorName":" xxxx","VisitorPhon":"","VisitorAddr":"xxxx","GeoCode":"","AutoKey":1},{"VisitorID":"09005468","VisitorName":"xxxxxx","VisitorPhon":"09005468","VisitorAddr":"xxxx","GeoCode":"","AutoKey":2}]}
and i wanna read and show information from this file to a ListView
my VisitorsListActivity is:
public class VisitorsListActivity extends AppCompatActivity {
public ListView lstVisitors;
static VisitorsList visitorsList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.visitor_list);
try {
//********************************** COMELETE THIS SECTION *********************************************
new JsonHelper.GetJsonData(new JsonHelper.GetJsonData.AsyncResponse() {
#Override
public void processFinish(String output) {
try {
if (output == null) output = "";
if (output.equals("")) {
Toast.makeText(getApplicationContext(),
"No Visitor Founded",
Toast.LENGTH_LONG)
.show();
return;
}
//960105--------------------
else if (output.equals("401")) {
Toast.makeText(getApplicationContext(),
"Error 401",
Toast.LENGTH_LONG)
.show();
return;
}
//--------------------------------------
Log.i("LOG", "output" + output);
Gson gson = new Gson();
output = output.substring(1, output.length() - 1);
/*Toast.makeText(getApplicationContext(),
output,
Toast.LENGTH_LONG)
.show();*/
visitorsList = new VisitorsList();
visitorsList = gson.fromJson(output, VisitorsList.class);
} catch (Exception e) {
e.printStackTrace();
Toast.makeText(getApplicationContext(),
"exception",
Toast.LENGTH_LONG)
.show();
}
}
}).execute("http://192.168.1.162:8014/api/Visitors");
//************************************ visitor list is null :| *******************************************
/*if( visitorsList == null) {
Toast.makeText(getApplicationContext(),
"data is nul",
Toast.LENGTH_LONG)
.show();
}*/
AdapterVisitor customAdapter = new AdapterVisitor(this, R.layout.visitor_list, visitorsList.VisitorsList);
customAdapter.notifyDataSetChanged();
lstVisitors.setAdapter(customAdapter);
lstVisitors.requestFocus();
final ViewGroup layoutClear = (ViewGroup) findViewById(R.id.layoutClear);
layoutClear.setVisibility(View.GONE);
} catch (Exception e) {
e.getMessage();
}
} }
and VisitorsList:
public class VisitorsList {
public VisitorsList() {}
public ArrayList<Visitors> VisitorsList;}
Visitors:
public class Visitors {
public String VisitorID;
public String VisitorName;
public String VisitorPhon;
public String VisitorAddr;
public String GeoCode;
public int AutoKey;}
and always visitor list which created by Gson is null. i dont know maybe my problem is in reading from json or maybe visitors class ...
jsonhelper :
public class JsonHelper {
public static class GetJsonData extends AsyncTask<String, Void, String> {
public interface AsyncResponse {
void processFinish(String output);
}
public AsyncResponse delegate = null;
public GetJsonData(AsyncResponse delegate) {
this.delegate = delegate;
}
#Override
protected String doInBackground(String... strUrl) {
String str = strUrl[0];
URLConnection urlConn = null;
BufferedReader bufferedReader = null;
try {
URL url = new URL(str);
urlConn = url.openConnection();
urlConn.setReadTimeout(300000);
urlConn.setConnectTimeout(5000);
bufferedReader = new BufferedReader(new InputStreamReader(urlConn.getInputStream(), "utf-8"), 8);
StringBuffer stringBuffer = new StringBuffer();
String line;
while ((line = bufferedReader.readLine()) != null) {
stringBuffer.append(line);
}
String tmpJson = stringBuffer.toString().replace("\\", "");
return tmpJson;
} catch (Exception ex) {
ex.getMessage();
return null;
} finally {
if (bufferedReader != null) {
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
#Override
protected void onPostExecute(String response) {
delegate.processFinish(response);
}
}
public static class SetJsonData extends AsyncTask<String, Void, String> {
String responseServer;
public interface AsyncResponse {
void processFinish(String output);
}
public AsyncResponse delegate = null;
public SetJsonData(AsyncResponse delegate) {
this.delegate = delegate;
}
#Override
protected String doInBackground(String... param) {
URL url;
String response = null;
try {
url = new URL(param[0]);
HttpURLConnection conn = null;
conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(20000);
conn.setConnectTimeout(10000);//950718
conn.setRequestMethod("GET");
conn.setDoInput(true);
conn.setDoOutput(true);
OutputStream os = conn.getOutputStream();
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(os, "UTF-8"));
writer.write(param[1]);
writer.flush();
writer.close();
os.close();
int responseCode = conn.getResponseCode();
if (responseCode == HttpsURLConnection.HTTP_OK) {
String line;
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
while ((line = br.readLine()) != null) {
response += line;
}
} else {
response = (String.valueOf(responseCode));
String line;
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getErrorStream()));//950427
while ((line = br.readLine()) != null) {
}
}
return response;
} catch (IOException e1) {
e1.getMessage();
return null;
} catch (Exception e) {
e.getMessage();
return null;
}
}
#Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
try {
super.onPostExecute(result);
delegate.processFinish(result);
} catch (Exception e) {
e.getMessage();
}
}
}}
your visitors class is missing annotations.
use this to convert it properly:
http://www.jsonschema2pojo.org/
Check this https://kylewbanks.com/blog/Tutorial-Android-Parsing-JSON-with-GSON
to read the JSON with GSON.
well at first read AsyncResponse so you are using asynchronous request is that what are doing ?
An asynchronous request doesn't block the client so it continue executing the code when the response is back it will execute what is inside the callback.
But you are calling the customAdapter.notifyDataSetChanged(); outside processFinish() you need to call it inside or call the Adapter work inside the processFinish method.
public class VisitorsList {
public VisitorsList() {}
public ArrayList VisitorsList= new ArrayList<>();}
Should be like this... Intialization is missing.
VisitorsList class :
public class VisitorsList {
#SerializedName("VisitorsList")
public List<VisitorsList> VisitorsList;
public static class VisitorsList {
#SerializedName("VisitorID")
public String VisitorID;
#SerializedName("VisitorName")
public String VisitorName;
#SerializedName("VisitorPhon")
public String VisitorPhon;
#SerializedName("VisitorAddr")
public String VisitorAddr;
#SerializedName("GeoCode")
public String GeoCode;
#SerializedName("AutoKey")
public int AutoKey;
}
}
delete this line
output = output.substring(1, output.length() - 1);
and get your result:
Gson gson = new Gson();
visitorsList=gson.fromJson(output), new TypeToken<VisitorsList>() { }.getType());
i change VisitorsListActivity same as below . and set a condition before call adapter to be sure reading information from json has been finished, this worked correctly :
new JsonHelper.GetJsonData(new JsonHelper.GetJsonData.AsyncResponse() {
#Override
public void processFinish(String output) {
try {
if (output == null) output = "";
if (output.equals("")) {
Toast.makeText(getApplicationContext(),
"No Visitor Founded",
Toast.LENGTH_LONG)
.show();
return;
}
else if (output.equals("401")) {
Toast.makeText(getApplicationContext(),
"Error 401",
Toast.LENGTH_LONG)
.show();
return;
}
Log.i("LOG", "output" + output);
Gson gson = new Gson();
output = output.substring(1, output.length() - 1);
try {
visitorsList = new VisitorsList();
visitorsList = gson.fromJson(output, VisitorsList.class);
if(visitorsList != null) {
d.cancel();
adapter = new AdapterVisitor(visitorsList.VisitorsList);
adapter.notifyDataSetChanged();
lstVisitors.setAdapter(adapter);
lstVisitors.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// ******
Object o = lstVisitors.getItemAtPosition(position);
Intent i = new Intent(getApplicationContext(),DateSelectorActivity.class);
Visitors v = (Visitors) o;
i.putExtra("VisitorID", v.VisitorID);
startActivity(i);
}
});
}
}catch (Exception e) {
Log.i("LOG", getAssets().toString() + "exception" + e);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}).execute(url);
I try to execute an AsyncTask like this
private static final String REQUESTED_URL = "//my url";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.earthquake_activity);
EarthQuakeAsyncTask task = new EarthQuakeAsyncTask();
task.execute(REQUESTED_URL); //this is where the error is
}
but Android Studio said that it cannot resolve method execute(String). I'm having a tutorial from Udacity, their sample is pretty much similar
/** URL for earthquake data from the USGS dataset */
private static final String USGS_REQUEST_URL =
"//url";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
EarthquakeAsyncTask task = new EarthquakeAsyncTask();
task.execute(USGS_REQUEST_URL); //it works
}
Can someone tell me why this possibly occurs?
Edit: this is my EarthQuakeAsyncTask class:
private class EarthQuakeAsyncTask extends AsyncTask<URL,Void,ArrayList<EarthQuake>> {
#Override
protected ArrayList<EarthQuake> doInBackground(URL... urls) {
if(urls.length==0||urls[0]== null){
return null;
}
// Create URL object
URL url = createUrl(REQUESTED_URL);
try {
jsonResponse = makeHttpRequest(url);
} catch (IOException e) {
// TODO Handle the IOException
}
ArrayList<EarthQuake> earthquake = QueryUtils.extractEarthquakes(jsonResponse);
return earthquake;
}
#Override
protected void onPostExecute(ArrayList<EarthQuake> earthquake) {
if (earthquake == null) {
return;
}
updateUi();
}
private URL createUrl(String stringUrl) {
URL url;
try {
url = new URL(stringUrl);
} catch (MalformedURLException exception) {
Log.e(LOG_TAG, "Error with creating URL", exception);
return null;
}
return url;
}
private String makeHttpRequest(URL url) throws IOException {
// If the URL is null, then return early.
if (url == null) {
return jsonResponse;
}
HttpURLConnection urlConnection = null;
InputStream inputStream = null;
try {
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setReadTimeout(10000 /* milliseconds */);
urlConnection.setConnectTimeout(15000 /* milliseconds */);
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// If the request was successful (response code 200),
// then read the input stream and parse the response.
if (urlConnection.getResponseCode() == 200) {
inputStream = urlConnection.getInputStream();
jsonResponse = readFromStream(inputStream);
} else {
Log.e(LOG_TAG, "Error response code: " + urlConnection.getResponseCode());
}
} catch (IOException e) {
Log.e(LOG_TAG, "Problem retrieving the earthquake JSON results.", e);
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (inputStream != null) {
inputStream.close();
}
}
return jsonResponse;
}
private String readFromStream(InputStream inputStream) throws IOException {
StringBuilder output = new StringBuilder();
if (inputStream != null) {
InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
BufferedReader reader = new BufferedReader(inputStreamReader);
String line = reader.readLine();
while (line != null) {
output.append(line);
line = reader.readLine();
}
}
return output.toString();
}
}
}
Your class signature suggests that you are expecting a URL type as parameter, but you are passing a String type in the execute() method. All you need to do is to change your class signature to expect a String as in the one in this code.
private class EarthQuakeAsyncTask extends AsyncTask<String,Void,ArrayList<EarthQuake>> {
#Override
protected ArrayList<EarthQuake> doInBackground(String... urls) {
if(urls.length==0||urls[0]== null){
return null;
}
// Create a URL object from the String passed to the execute method
URL url = createUrl(urls[0]);
try {
jsonResponse = makeHttpRequest(url);
} catch (IOException e) {
// TODO Handle the IOException
}
ArrayList<EarthQuake> earthquake = QueryUtils.extractEarthquakes(jsonResponse);
return earthquake;
}
#Override
protected void onPostExecute(ArrayList<EarthQuake> earthquake) {
if (earthquake == null) {
return;
}
updateUi();
}
private URL createUrl(String stringUrl) {
URL url;
try {
url = new URL(stringUrl);
} catch (MalformedURLException exception) {
Log.e(LOG_TAG, "Error with creating URL", exception);
return null;
}
return url;
}
private String makeHttpRequest(URL url) throws IOException {
// If the URL is null, then return early.
if (url == null) {
return jsonResponse;
}
HttpURLConnection urlConnection = null;
InputStream inputStream = null;
try {
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setReadTimeout(10000 /* milliseconds */);
urlConnection.setConnectTimeout(15000 /* milliseconds */);
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// If the request was successful (response code 200),
// then read the input stream and parse the response.
if (urlConnection.getResponseCode() == 200) {
inputStream = urlConnection.getInputStream();
jsonResponse = readFromStream(inputStream);
} else {
Log.e(LOG_TAG, "Error response code: " + urlConnection.getResponseCode());
}
} catch (IOException e) {
Log.e(LOG_TAG, "Problem retrieving the earthquake JSON results.", e);
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (inputStream != null) {
inputStream.close();
}
}
return jsonResponse;
}
private String readFromStream(InputStream inputStream) throws IOException {
StringBuilder output = new StringBuilder();
if (inputStream != null) {
InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
BufferedReader reader = new BufferedReader(inputStreamReader);
String line = reader.readLine();
while (line != null) {
output.append(line);
line = reader.readLine();
}
}
return output.toString();
}
}
}
That is because your AsyncTask class isn't defined in a manner to handle the execute method with a String parameter. Let me explain myself.
The AsyncTask class you develop will look like this:
private class MyAsyncTask extends AsyncTask<TYPE1, TYPE2, TYPE3> {
protected TYPE3 doInBackground(TYPE1... type1_variables) {
// Do some long process here..
return variable_of_type_TYPE3;
}
protected void onPostExecute(TYPE3 result) {
// Do something here
}
}
So for you to call task.execute(REQUESTED_URL); you'd need to implement your AsyncTask class correctly.
For example it might look like this:
private class EarthQuakeAsyncTask extends AsyncTask<String, Void, Void> {
...
}
In here the code with BufferedReaderand line = reader.readLine() works
public class WeatherService extends AsyncTask<TaskParams, Void, String> {
private WeatherServiceCallback callback;
private Exception exception;
public WeatherService(WeatherServiceCallback callback) {
this.callback = callback;
}
#Override
protected String doInBackground(TaskParams... params) {
try {
URL url = new URL("http://api.openweathermap.org/data/2.5/weather?lat=" +
params[0].getLat() + "&lon=" + params[0].getLon() +
"&units=" + TaskParams.getUnits() +
"&type=" + TaskParams.getAccuracy() + "&lang=" + TaskParams.getLanguage() +
"&appid=10660a09a9fb335d72f576f7aa1bbe5b");
URLConnection connection = url.openConnection();
InputStream inputStream = connection.getInputStream();
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 (MalformedURLException e) {
exception = e;
} catch (IOException e) {
exception = e;
}
return null;
}
#Override
protected void onPostExecute(String s)
{
if (s == null && exception != null)
{
callback.serviceFailure(exception);
return;
}
try
{
JSONObject data = new JSONObject(s);
Parameters parameters = new Parameters();
parameters.poopulate(data);
callback.serviceSuccess(parameters);
} catch (JSONException e) {
e.printStackTrace();
}
}
}
I copy-pasted code to other class since it has very similar functionality and now for no reason I'm getting NullPointerException in while ((line = reader.readLine()) != null) and I have no idea why since as I said it's copy-pasted (I only changed URL and object returned if serivce succeeds)
public class PollutionService extends AsyncTask<TaskParams, Void, String>
{
private PollutionServiceCallback callback;
private Exception exception;
private URLConnection connection;
private InputStream inputStream;
private InputStreamReader streamReader;
private BufferedReader reader;
public PollutionService(PollutionServiceCallback callback) {
this.callback = callback;
}
#Override
protected String doInBackground(TaskParams... params) {
try
{
URL url = new URL("http://api.openweathermap.org/pollution/v1/co/" + params[0].getLat() +
"," + params[0].getLon() + "/current.json?&appid=10660a09a9fb335d72f576f7aa1bbe5b");
try
{
connection = url.openConnection();
}
catch (IOException e)
{
exception = new Exception("Connection error");
}
try
{
inputStream = connection.getInputStream();
}
catch (IOException e)
{
exception = new Exception("Input stream error");
}
try
{
streamReader = new InputStreamReader(inputStream);
}
catch (NullPointerException e)
{
exception = new Exception("Input stream reader error");
}
try
{
reader = new BufferedReader(streamReader);
}
catch (NullPointerException e)
{
exception = new Exception("Buffered reader error");
}
StringBuilder builder = new StringBuilder();
String line;
try
{
while ((line = reader.readLine()) != null)
{
builder.append(line);
}
}
catch (IOException e)
{
exception = e;
}
return builder.toString();
}
catch (MalformedURLException e)
{
exception = e;
}
return null;
}
#Override
protected void onPostExecute(String s)
{
if (s == null && exception != null)
{
callback.pollutionServiceFailure(exception);
return;
}
try
{
JSONObject data = new JSONObject(s);
PollutionParameters parameters = new PollutionParameters();
parameters.poopulate(data);
callback.pollutionServiceSuccess(parameters);
} catch (JSONException e) {
e.printStackTrace();
}
}
}
Any clue?
EDIT
This is rewritten code for PollutionActivity. Callback function serviceFailure prints now the URL address on my phone's screen
public class PollutionService extends AsyncTask<TaskParams, Void, String>
{
private PollutionServiceCallback callback;
private Exception exception;
public PollutionService(PollutionServiceCallback callback) {
this.callback = callback;
}
#Override
protected String doInBackground(TaskParams... params) {
try
{
URL url = new URL("http://api.openweathermap.org/pollution/v1/co/" + params[0].getLat() +
"," + params[0].getLon() + "/current.json?&appid=10660a09a9fb335d72f576f7aa1bbe5b");
URLConnection connection = url.openConnection();
InputStream inputStream = connection.getInputStream();
InputStreamReader streamReader = new InputStreamReader(inputStream);
BufferedReader reader = new BufferedReader(streamReader);
StringBuilder builder = new StringBuilder();
String line;
try
{
while ((line = reader.readLine()) != null)
{
builder.append(line);
}
}
catch (IOException e)
{
exception = e;
}
return builder.toString();
}
catch (MalformedURLException e)
{
exception = e;
}
catch (IOException e)
{
exception = e;
}
return null;
}
#Override
protected void onPostExecute(String s)
{
if (s == null && exception != null)
{
callback.pollutionServiceFailure(exception);
return;
}
try
{
JSONObject data = new JSONObject(s);
PollutionParameters parameters = new PollutionParameters();
parameters.poopulate(data);
callback.pollutionServiceSuccess(parameters);
} catch (JSONException e) {
e.printStackTrace();
}
}
}
Debugging showed me that code jumps to exception after
InputStream inputStream = connection.getInputStream();
If you are getting NPE for reader then it means that reader is not getting initialized and going null.Your code is getting crash at line 23 and 89. So I believe that the problem is right at the start somewhere and not at the point itself, may be some object is going null like connection.Since line number is not displayed here.Check null pointer for every object like if (connection!=null). Since the initial data is coming null,maybe input stream or some other data,hence your reader object is not getting initialized.Also check if you are getting value for every object in debug.