I shoul use setText() but how should I use it instead of System.out.println()?
I want to print the result in a TextView. The code is a json reader. sorry I need to write some text to let me post my question.
public class JsonReader extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
private static String readAll(Reader rd) throws IOException {
StringBuilder sb = new StringBuilder();
int cp;
while ((cp = rd.read()) != -1) {
sb.append((char) cp);
}
return sb.toString();
}
public static JSONObject readJsonFromUrl(String url) throws IOException, JSONException {
InputStream is = new URL(url).openStream();
try {
BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
String jsonText = readAll(rd);
JSONObject json = new JSONObject(jsonText);
return json;
} finally {
is.close();
}
}
public static void main(String[] args) throws IOException, JSONException {
JSONObject json = readJsonFromUrl("http://www.w3schools.com/json/myTutorials.txt");
System.out.println(json.toString());
System.out.println(json.get("display"));
//TextView tv = (TextView) findViewById( R.id.tv );
//tv.setText(json.toString());
//tv.setText(json.get("display"));
}
}
You will need to print the result in a TextView if you want to view the result on phone instead of LogCat console as suggested by johnrao07.
To print result in a TextView first add a TextView widget in activity_main.xml layout file.
<TextView
android:id="#+id/text_view_id"
android:layout_width="match_parent"
android:layout_height="match_parent" />
Then JsonReader.java class main function instead of System.out.println(json.toString()); call ((TextView) findViewById(R.id.text_view_id)).setText(json.toString());
You need to use Logs to print and debug stuff in android.
Generally there are five methods,
Log.v() Log.d() Log.i() Log.w() and Log.e()
v for Verbose
d for Debug
i for Info
w for Warnings
e for Error
In your case
Log.d("Key", json.toString() + "");
Log.d("Key", json.get("display") + "");
And you look for the values in the log cat, using the "Key"
You can use a CharArrayWriter to collect the output:
CharArrayWriter writer = new CharArrayWriter();
// write your stuff
TextView view = ...
view.setText(writer.toString());
You'll have to use the methods available to a Writer rather than those of a PrintStream such as System.out (no println() methods).
If you want to use basically the same calls to generate the output, you can create a ByteArrayOutputStream and wrap it in a PrintStream. After writing (and closing the PrintStream), retrieve the byte array from the ByteArrayOutputStream and convert it to a String using one of the String constructors. You just have to specify the character encoding you want to use, both when creating the PrintStream and when converting the bytes to a String.
Another alternative would be to replace printing with simply appending your data to a StringBuilder.
A final alternative is simply to append directly to the TextView, but that requires converting every piece of output to some sort of CharSequence.
public class JsonReader extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Thread(new Runnable(){
public void run(){
JSONObject json = readJsonFromUrl("http://www.w3schools.com/json/myTutorials.txt");
System.out.println(json.toString());
System.out.println(json.get("display"));
runOnUiThread(new Runnable(){
public void run(){
TextView tv = (TextView) findViewById( R.id.tv );
tv.setText(json.toString());
tv.setText(json.get("display"));
}
});
}
}).start();
}
private static String readAll(Reader rd) throws IOException {
StringBuilder sb = new StringBuilder();
int cp;
while ((cp = rd.read()) != -1) {
sb.append((char) cp);
}
return sb.toString();
}
public static JSONObject readJsonFromUrl(String url) throws IOException, JSONException {
InputStream is = new URL(url).openStream();
try {
BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
String jsonText = readAll(rd);
JSONObject json = new JSONObject(jsonText);
return json;
} finally {
is.close();
}
}
public static void main(String[] args) throws IOException, JSONException {
//move to onCreate
}
}
Related
I am getting a java.lang.NullPointerException error when storing xml data parsed from a URL on my localhost (http://10.0.0.22/cardealers.xml) to sql. Here is the xml am parsing:
<Providers>
<CarDealer name="BEFORWARD" id="1">
<CarMake name="Toyota" id="20">
<CarModel name="Belta" id="21"/>
<CarModel name="RunX" id="22"/>
<CarModel name="Corolla" id="23"/>
</CarMake>
<CarMake name="Nissan" id="30">
<CarModel name="Murano" id="31"/>
<CarModel name="Pathfinder" id="32"/>
<CarModel name="Navara" id="33"/>
</CarMake>
</CarDealer>
</Providers>
In my xml handler class, I passed my xml like so:
public class SAXXMLHandler extends DefaultHandler {
private List<CarMake> carMaker;
private String tempVal;
// to maintain context
private CarMake carmake;
public SAXXMLHandler() {
carMaker = new ArrayList<CarMake>();
}
public List<CarMake> getCarMake() {
return carMaker;
}
// Event Handlers
public void startElement(String uri, String localName, String qName,
Attributes attributes) throws SAXException {
// reset
tempVal = "";
if (qName.equalsIgnoreCase("CarMake")) {
// create a new instance of CarMake
carmake = new CarMake();
carmake.setName(attributes.getValue("name"));
}
}
public void characters(char[] ch, int start, int length)
throws SAXException {
tempVal = new String(ch, start, length);
}
public void endElement(String uri, String localName, String qName)
throws SAXException {
if (qName.equalsIgnoreCase("CarMake")) {
// add it to the list
carMaker.add(carmake);
} else if (qName.equalsIgnoreCase("CarModel")) {
carmake.setCarModel(tempVal);
}
}
}
Then using AsyncTask in Sell.java
public class Sell extends Activity implements
View.OnClickListener, AdapterView.OnItemClickListener {
static final String URL = "http://10.0.0.22/cardealers.xml";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sell);
//new GetXMLTask().execute();
new GetXMLTask(this).execute();
}
#Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
}
#Override
public void onClick(View view) {
GetXMLTask task = new GetXMLTask(this);
task.execute(new String[]{URL});
}
//private inner class extending AsyncTask
private class GetXMLTask extends AsyncTask<String, Void, List<Service>> {
private Activity context;
public GetXMLTask(Activity context) {
this.context = context;
}
/* uses HttpURLConnection to make Http request from Android to download
the XML file */
private String getXmlFromUrl(String urlString) {
StringBuffer output = new StringBuffer("");
try {
InputStream stream = null;
URL url = new URL(urlString);
URLConnection connection = url.openConnection();
HttpURLConnection httpConnection = (HttpURLConnection) connection;
httpConnection.setRequestMethod("GET");
httpConnection.connect();
if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
stream = httpConnection.getInputStream();
BufferedReader buffer = new BufferedReader(
new InputStreamReader(stream));
String s = "";
while ((s = buffer.readLine()) != null)
output.append(s);
}
} catch (Exception ex) {
ex.printStackTrace();
}
return output.toString();
}
#Override
protected List<CarMake> doInBackground(String... urls) {
List<CarMake> carMaker = null;
String xml = null;
for (String url : urls) {
xml = getXmlFromUrl(url);
InputStream stream = new ByteArrayInputStream(xml.getBytes());
carMaker = SAXXMLParser.parse(stream);
}
// stream.close();
return carMaker;
}
#Override
protected void onPostExecute(List<CarMake> carMaker) {
if (carMaker==null){
Toast.makeText(Sell.this, "carMaker is empty..", Toast.LENGTH_LONG).show();
} else {
E_VodaDB myE_Voda = new E_VodaDB(this.context);
myE_Voda.InsertData(carMaker);
}
}
}
}
As can be seen, my doInBackground() returns a result, carMaker. Then in my OnPostExecute(), I am passing the carMaker arraylist to my databases class to insert in db.
// Adding new service
public void InsertData(List<CarMake> carMaker) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(CARMAKE_NAME, carMaker.get(0).getCarMake()); // CarMake Names
// Inserting Row
db.insert(TABLE_CARDEALER, null, values);
db.close(); // Closing database connection
}
}
I get the following error when I run the app in Android Studio:
java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference
Pointing to my Sell.java in my onPostExecute(). It seems the carMaker arraylist returned from doInBackground() is empty or it is in a different data type that cannot be directly stored into db. How would I go about fixing this error? Please note am a newbie to android
on doInBackground() you create arraylist but forget to initialize. try this.
#Override
protected List<CarMake> doInBackground(String... urls) {
List<CarMake> carMaker = new ArrayList<CarMake>();
String xml = null;
for (String url : urls) {
xml = getXmlFromUrl(url);
InputStream stream = new ByteArrayInputStream(xml.getBytes());
carMaker = SAXXMLParser.parse(stream);
}
// stream.close();
return carMaker;
}
you pass the null instance of current class context in this:
#Override
protected void onPostExecute(List<CarMake> carMaker) {
//E_DB myE_db = new E_DB(null);// replace this to
E_DB myE_db = new E_DB(this);
myE_db.InsertData(carMaker);
}
}
Happy coding!!
Below is my code, lat_val and long_val is not getting updated with received value from JSON response in btnShowLoc(), it is referencing to the default value which is 0,0. I want the global variable to keep updating when ever referenced and updated with JSON response.
public class MainActivity extends Activity {
public static String lat_val = "0";
public static String long_val = "0";
public String readJSONFeed(String urlStr) {
StringBuilder stringBuilder = new StringBuilder();
try {
URL url = new URL(urlStr);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestProperty("SisApiKey", "4572c3c9-73cb-4958-9649-26c1e8df27e8");
urlConnection.setRequestProperty("SisSmartKey", "d1aebd25-774c-4e8a-b3a5-ee5a603cc603");
InputStream ins = urlConnection.getInputStream();
urlConnection.connect();
int statusCode = urlConnection.getResponseCode();
if (statusCode == 200) {
BufferedReader br = new BufferedReader(new InputStreamReader(ins));
String line;
while ((line = br.readLine()) != null) {
stringBuilder.append(line);
}
ins.close();
} else {
Log.d("JSON", "Failed to download file");
}
} catch (java.net.MalformedURLException e) {
e.printStackTrace();
} catch (java.io.IOException e) {
e.printStackTrace();
} catch (Exception e) {
Log.d("readJSONFeed", e.getLocalizedMessage());
}
return stringBuilder.toString();
}
public class ReadJSONFeedTask extends AsyncTask
<String, Void, String> {
protected String doInBackground(String... url) {
return readJSONFeed(url[0]);
}
protected void onPostExecute(String result) {
try {
JSONObject jsonObject = new JSONObject(result);
//JSONObject flags = new JSONObject(jsonObject.getString("flag"));
JSONObject locationItems = new JSONObject(jsonObject.getString("response"));
//Log.v("Location Details :", locationItems.toString());
String []dev_loc = locationItems.toString().split("[\\s*,\\s*]");
MainActivity.lat_val = dev_loc[0]; //"12.9934136";
MainActivity.long_val = dev_loc[1]; //"80.2464206";
} catch (Exception e) {
Log.d("ReadJSONFeedTask", e.getLocalizedMessage());
}
}
}
public void btnGetDevLoc(View view) {
String sp_val = String.valueOf(spinner1.getSelectedItem());
new ReadJSONFeedTask().execute(
"http://15.153.133.160:21743/sis/sie/api/v1/applications/bb9f05fb-a796-4b75-9db7-c999360ad185/virtualobjects/d77d3905-aa77-41b9-9034-b0052bfde405?secondString=HWE_ASSET_ANDROID"); // + sp_val);
}
public void btnShowLoc(View view) {
//lat_val = "12.9934136";
//long_val = "80.2464206";
Intent in = new Intent(MainActivity.this, MapActivity.class);
Bundle bundle = new Bundle();
bundle.putString("latitude", MainActivity.lat_val);
bundle.putString("longitude", MainActivity.long_val);
in.putExtras(bundle);
startActivity(in);
}
With the few information you have shared, and given that
btnGetDevLoc() and btnShowLoc()are the functions executed when clicked on buttons in the application defined in activity_main.xml
and that
First btnGetDevLoc() is called then btnShowLoc()
the first thing that pops out in my mind is that the AsyncTask has not yet finished updating the String values, when you call btnShowLoc().
So, if btnGetDevLoc() and btnShowLoc() are called sequentially, like
... onClick() {
btnGetDevLoc();
btnShowLoc();
}
then it's most likely due to what I said above. Remember that AsyncTask runs asynchronously (as the name says...).
You can test this really small program.
public static double var1 = 0.0;
public static void main(String[] args) {
new Thread(() -> {
var1 = 1.0;
}).start();
System.out.println(var1);
}
It will almost always print 0.0, because the value of var1 is not updated yet when the main thread prints it.
What you should do is place your btnShowLoc() call at the end of onPostExecute(String). This guarantees that your method is called only after you have updated the new values.
I can't Understand, when the btnGetDevLoc() and btnShowLoc() called? Can you post your whole MainActivity?
Edit :
It's seems like you call btnShowLoc() before your AsyncTask finish its proccess.
You can change your code this way to make sure your btnShowLoc() called after your AsyncTask :
public class ReadJSONFeedTask extends AsyncTask
<String, Void, String> {
protected String doInBackground(String... url) {
return readJSONFeed(url[0]);
}
protected void onPostExecute(String result) {
try {
JSONObject jsonObject = new JSONObject(result);
//JSONObject flags = new JSONObject(jsonObject.getString("flag"));
JSONObject locationItems = new JSONObject(jsonObject.getString("response"));
//Log.v("Location Details :", locationItems.toString());
String []dev_loc = locationItems.toString().split("[\\s*,\\s*]");
MainActivity.lat_val = dev_loc[0]; //"12.9934136";
MainActivity.long_val = dev_loc[1]; //"80.2464206";
btnShowLoc(dev_loc[0], dev_loc[1]);
} catch (Exception e) {
Log.d("ReadJSONFeedTask", e.getLocalizedMessage());
}
}
}
public void btnShowLoc(String latitude, String longitude) {
//lat_val = "12.9934136";
//long_val = "80.2464206";
Intent in = new Intent(MainActivity.this, MapActivity.class);
Bundle bundle = new Bundle();
bundle.putString("latitude", latitude);
bundle.putString("longitude", longitude);
in.putExtras(bundle);
startActivity(in);
}
I'm trying to build a very basic weather app in android studio. I am using AsyncClass to return multiple strings.
As you can see in the code, I used a class named "Wrapper" that is used to store my strings so I can just return a class object and use it in the onPostExecute method of the AsyncTask. The problem I am facing is that when I test the app, all of the returned Strings somehow are undefined (the default for the Wrapper class). This means the strings are not being updated in the doInBackground method and I can't seem to figure out why!
My Activity
#Override
public void onConnectionFailed(ConnectionResult connectionResult) {
Log.i(MainActivity.class.getSimpleName(), "Can't connect to Google Play Services!");
}
private class Wrapper
{
String Temperature = "UNDEFINED";
String city = "UNDEFINED";
String country = "UNDEFINED";
}
private class GetWeatherTask extends AsyncTask<String, Void, Wrapper> {
private TextView textView;
public GetWeatherTask(TextView textView) {
this.textView = textView;
}
#Override
protected Wrapper doInBackground(String... strings) {
Wrapper w = new Wrapper();
String Temperature = "x";
String city = "y";
String country = "z";
try {
URL url = new URL(strings[0]);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
InputStream stream = new BufferedInputStream(urlConnection.getInputStream());
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(stream));
StringBuilder builder = new StringBuilder();
String inputString;
while ((inputString = bufferedReader.readLine()) != null) {
builder.append(inputString);
}
JSONObject topLevel = new JSONObject(builder.toString());
JSONObject main = topLevel.getJSONObject("main");
JSONObject cityobj = topLevel.getJSONObject("city");
Temperature = String.valueOf(main.getDouble("temp"));
city = cityobj.getString("name");
country = cityobj.getString("country");
w.Temperature= Temperature;
w.city= city;
w.country=country;
urlConnection.disconnect();
} catch (IOException | JSONException e) {
e.printStackTrace();
}
return w;
}
#Override
protected void onPostExecute(Wrapper w) {
textView.setText("Current Temperature: " + w.Temperature + " C" + (char) 0x00B0
+"\n" + "Current Location: "+ w.country +"\n" + "City: "+ w.city );
}
}
}
UPDATE:
turned out that that I was using the wrong url in my code,I was using :
http://api.openweathermap.org/data/2.5/weather?lat=%f&lon=%f&units=%s&appid=%s
Instead I should've been using:
http://api.openweathermap.org/data/2.5/forecast?lat=%f&lon=%f&units=%s&appid=%s
-aka instead of weather I should've been using forcast
Your error starts here
JSONObject main = topLevel.getJSONObject("main");
Probably because the topLevel object has no "main" key.
{
"city":{ },
"cod":"200",
"message":0.1859,
"cnt":40,
"list":[ ]
}
Throw your JSON into here. https://jsonformatter.curiousconcept.com/
You'll notice that there are many, many "main" keys that are within the "list" element, but you have to parse those starting from getJSONArray("list").
Basically, something like this
String city = "undefined";
String country = "undefined";
List<Double> temperatures = new ArrayList<Double>();
try {
JSONObject object = new JSONObject(builder.toString());
JSONObject jCity = object.getJSONObject("city");
city = jCity.getString("name");
country = jCity.getString("country");
JSONArray weatherList = object.getJSONArray("list");
for (int i = 0; i < weatherList.length(); i++) {
JSONObject listObject = weatherList.getJSONObject(i);
double temp = listObject.getJSONObject("main").getDouble("temp");
temperatures.add(temp);
}
} catch (JSONException e) {
e.printStackTrace();
}
return new Wrapper(city, country, temperatures);
After studying your code, either your try block is failing, which is returning your object, but empty, or there is something wrong with your JSON parsing. If you could show us the JSON you are trying to parse that would be a great help.
That being said, the fact that it is still showing as "UNDEFINED" is because that is how you initialised it, and becuase (the JSON parse is likely failing), the object is being returned in an un-edited state.
EDIT:
You are parsing the JSON wrong. You are trying to find an object called "main" in the top directory, however the main object only exists inside of an array called list!
Please look here for a more easy to see and visual representation: http://prntscr.com/dlhlrk
You can use this site to help visualise your JSON and create an appropriate soluton based upon it. https://jsonformatter.curiousconcept.com/
Looking at the API you posted earlier (api.openweathermap.org) you are trying to access variables that don't exist. I suggest you have a look at what the API returns and try getting the variables one by one if you are getting a JSONException
EDIT:
What API you are using? In your initial post you said it was http://api.openweathermap.org/data/2.5/weather but in a comment above you said it was http://api.openweathermap.org/data/2.5/forecast.
If you're using the weather API (as initially stated) you can use the below:
#Override
protected Wrapper doInBackground(String... strings) {
Wrapper w = new Wrapper();
try {
URL url = new URL(strings[0]);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
InputStream stream = new BufferedInputStream(urlConnection.getInputStream());
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(stream));
StringBuilder builder = new StringBuilder();
String inputString;
while ((inputString = bufferedReader.readLine()) != null) {
builder.append(inputString);
}
Log.d("JSON", builder.toString());
JSONObject topLevel = new JSONObject(builder.toString());
JSONObject main = topLevel.getJSONObject("main");
JSONObject sys = topLevel.getJSONObject("sys");
w.Temperature = String.valueOf(main.getDouble("temp"));
w.city = topLevel.getString("name");
w.country = sys.getString("country");
urlConnection.disconnect();
} catch (IOException | JSONException e) {
e.printStackTrace();
}
return w;
}
I am trying to figure out how to save my Todo List in a file and then obtain it when I reopen the application. So far, my entries are saving to file correctly as a string, but I don't know how to get them back out of the string and display on screen. I guess I have to deserialize it, but I don't know how that works and would really appreciate some help.
This is a sample of my code:
MainActivity.java
public class MainActivity extends AppCompatActivity {
ArrayList<Entry> mEntries;
String json;
Gson gson;
File dir, saveLocation;
FileWriter file1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
gson = new Gson();
try {
BufferedReader br = new BufferedReader(new FileReader(new File(dir,"storage.json")));
Entry e = gson.fromJson(br, Entry.class);
//I'm stuck here, Don't know how to proceed
} catch (FileNotFoundException e) {
e.printStackTrace();
}
#Override
protected void onStop() {
super.onStop();
json = gson.toJson(mEntries);
Log.d("jsondata", json);
try {
dir = getFilesDir();
saveLocation = new File(dir,"storage.json");
file1 = new FileWriter(saveLocation);
file1.write(json);
file1.flush();
file1.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
Entry.java
public class Entry {
String S;
boolean b;
public Entry(String S, boolean b) {
this.S = S;
this.b = b;
}
//Getter and Setter methods
A sample of the json saved in the file:
[{"S":"hello there","b":false},{"S":"task1","b":true},{"S":"task2","b":false}]
// Here S is the task to do and b is whether it is done or not
Your code is correct.
Entry e = gson.fromJson(br, Entry.class);
This line of code has already deserialized the string.
since your file contain Json array, you should parse it into array of Entry rather than single instance of Entry, for example:
BufferedReader br = new BufferedReader(new FileReader(new File(dir,"storage.json")));
Entry[] entries = gson.fromJson(br, Entry[].class);
it's my first question here, i've try to be the more explicit :)
I want get value from a JSON page : https://api.dailymotion.com/video/x3p6d9r?fields=onair.
I have follow a tutorial about json object.
But i want get the value "onair" and put this in a String for use a IF STRING == "XX".
This is my code :
public class notification extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_notification);
detectonline();
}
public void detectonline(){
/*
if (xx == "false") {
Do something is live is off
}
else{
Do something is live is on
}
*/
}
public static boolean checkIfOnline(String channel) throws IOException {
String channerUrl = "https://api.dailymotion.com/video/x3p6d9r?fields=onair";
String jsonText = readFromUrl(channerUrl);// reads text from URL
JsonParser parser = new JsonParser();
JsonObject json = parser.parse(jsonText).getAsJsonObject();
return !json.get("onair").isJsonNull();
}
private static String readFromUrl(String url) throws IOException {
URL page = new URL(url);
StringBuilder sb = new StringBuilder();
Scanner scanner = null;
try{
//scanner = new Scanner(page.openStream(), StandardCharsets.UTF_8.name());
scanner = new Scanner(page.openStream());
while (scanner.hasNextLine()){
sb.append(scanner.nextLine());
}
}finally{
if (scanner!=null)
scanner.close();
}
return sb.toString();
}
}
I remake your method according what you are looking for it's one of several way to parse json data :
public static boolean checkIfOnline(String channel) throws JSONException, IOException {
String channerUrl = "https://api.dailymotion.com/video/x3p6d9r?fields=onair";
String jsonText = readFromUrl(channerUrl);// reads text from URL
JSONObject json = new JSONObject(jsonText); // You create a json object from your string jsonText
if(json.has("onair")) { // just a simple test to check the node that you need existe
boolean value = json.getBoolean("onair"); // In the url that you gave onair value is boolean type
return value;
}
return false;
}
I will create methode using your way !
public static boolean checkIfOnline(String channel) throws IOException {
String channerUrl = "https://api.dailymotion.com/video/x3p6d9r?fields=onair";
String jsonText = readFromUrl(channerUrl);// reads text from URL
JsonParser parser = new JsonParser();
String myString =json.get("onair");
return mystring;}