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);
Related
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 developing android app and now I have problem. Below is a part of my code, and it keeps skipping the "for" part. When I put a breakpoint inside for statement, it stops at the point, and executes the lines very well and makes an output that I want. When I just 'run' app, it skips that part so "String locations" value doesn't change. I googled and some say it's thread-related problem. So I put synchroinzed on the method, still not working. Any other suggestions?
UPDATE
I was trying to show code only related to the problem, but I think now showing the whole would be more useful for those who try to help so here's my entire code on showMapActivity. You can see I've tried some ways around and nothing worked. Saving path's information into String url is where I'm having problem. I tested, and other parts seem to work fine. I know my code is really massy, that was why I only posted parts of the code. TMap related classes are imported from .jar file.
public class showMapActivity extends Activity {
TMapData tmapdata=new TMapData();
TMapView tmapView;
TMapPoint origin, dest;
volatile ArrayList<TMapPoint> points=new ArrayList<>();
private TextView x;
private TextView y;
private HashMap<String,LatLng> coordinates;
private HashMap<LatLng,Double> finalpoint;
static private ConcurrentHashMap<Double,Double> path;
#Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_show_map);
coordinates=new HashMap<>();
Intent intent=getIntent();
tmapView=new TMapView(this);
path=new ConcurrentHashMap<>();
coordinates=(HashMap<String,LatLng>)intent.getSerializableExtra("coordinate");
path=getPathPoints(coordinates);
int i=0;
String url=getUrl();
//String url = "https://maps.googleapis.com/maps/api/elevation/json?locations=";
//String locations="";
/*
Iterator<Double> keys= path.keySet().iterator();
while(keys.hasNext()){
Double key=keys.next();
//String lat=String.valueOf(key);
//String lng=String.valueOf(path.get(key));
locations=locations+String.valueOf(key)+","+String.valueOf(path.get(key));
if(keys.hasNext())
locations=locations+"|";
}path.entrySet()
*/
/*
for(ConcurrentHashMap.Entry<Double,Double> elem : path.entrySet())
{
String lat=String.valueOf(elem.getKey());
String lng=String.valueOf(elem.getValue());
locations=locations+lat+","+lng;
i++;
if(i!=path.size())
{
locations=locations+"|";
}
}
*/
//url=url+locations+"&key=AIzaSyDD88VFMPIfC5sr0XsFL0PDCE-QRN8gQto";
//String url=getUrl(path);
FetchUrl fetchUrl=new FetchUrl();
fetchUrl.execute(url);
}
private ConcurrentHashMap<Double,Double> getPathPoints(HashMap<String,LatLng> coordinates)
{
final ConcurrentHashMap<Double,Double> Path=new ConcurrentHashMap<>();
tmapView.setSKPMapApiKey("6bb5b7f3-1274-3c5e-ba93-790aee876673");
origin=new TMapPoint(coordinates.get("origin").latitude,coordinates.get("origin").longitude);
dest=new TMapPoint(coordinates.get("dest").latitude,coordinates.get("dest").longitude);
tmapdata.findPathData(origin, dest, new TMapData.FindPathDataListenerCallback() {
#Override
public void onFindPathData(TMapPolyLine polyLine) {
points=polyLine.getLinePoint();
for(TMapPoint point : points )
Path.put(point.getLatitude(),point.getLongitude());
}
});
return Path;
}
//ConcurrentHashMap<Double,Double> path
private synchronized String getUrl() {
int i=0;
String url = "https://maps.googleapis.com/maps/api/elevation/json?locations=";
String locations="";
for(HashMap.Entry<Double,Double> elem : path.entrySet())
{
String lat=String.valueOf(elem.getKey());
String lng=String.valueOf(elem.getValue());
locations=locations+lat+","+lng;
i++;
if(i!=path.size())
{
locations=locations+"|";
}
}
url=url+locations+"&key=AIzaSyDD88VFMPIfC5sr0XsFL0PDCE-QRN8gQto";
//https://maps.googleapis.com/maps/api/elevation/json?locations=
// 39.7391536,-104.9847034|36.455556,-116.866667&key=AIzaSyDD88VFMPIfC5sr0XsFL0PDCE-QRN8gQto
// Output format
return url;
}
private class FetchUrl extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... url) {
// For storing data from web service
String data = "";
try {
// Fetching the data from web service
//downloadURL
data = downloadUrl(url[0]);
Log.d("Background Task data", data.toString());
} catch (Exception e) {
Log.d("Background Task", e.toString());
}
return data;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
//ParserTask
ParserTask parserTask = new ParserTask();
// Invokes the thread for parsing the JSON data
parserTask.execute(result);
}
}
private String downloadUrl(String strUrl) throws IOException {
String data = "";
InputStream iStream = null;
HttpURLConnection urlConnection = null;
try {
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
//읽은 데이터를 버퍼에 저장
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while ((line = br.readLine()) != null) {
sb.append(line);
}
data = sb.toString();
Log.d("downloadUrl", data.toString());
br.close();
} catch (Exception e) {
Log.d("Exception", e.toString());
} finally {
iStream.close();
urlConnection.disconnect();
}
return data;
}
private class ParserTask extends AsyncTask<String, Integer, ArrayList<Double>> {
// Parsing the data in non-ui thread
#Override
protected ArrayList<Double> doInBackground(String... jsonData) {
JSONObject jObject;
ArrayList<Double> altitude = null;
try {
jObject = new JSONObject(jsonData[0]);
Log.d("ParserTask",jsonData[0].toString());
//DataParser class 호출
DataParser parser = new DataParser();
Log.d("ParserTask", parser.toString());
// Starts parsing data
altitude = parser.parse(jObject);
Log.d("ParserTask","Getting Altitudes");
Log.d("ParserTask",altitude.toString());
} catch (Exception e) {
Log.d("ParserTask",e.toString());
e.printStackTrace();
}
return altitude;
}
// Executes in UI thread, after the parsing process
#Override
protected void onPostExecute(ArrayList<Double> result) {
finalpoint=new HashMap<>();
LatLng latLng;
int i=0;
for(HashMap.Entry<Double,Double> elem : path.entrySet() )
{
latLng=new LatLng(elem.getKey(),elem.getValue());
finalpoint.put(latLng,result.get(i++));
}
x = (TextView) findViewById(R.id.textView5);
y = (TextView) findViewById(R.id.textView6);
x.setText(String.valueOf(finalpoint.get(coordinates.get("origin"))));
y.setText(String.valueOf(finalpoint.get(coordinates.get("dest"))));
}
}
}
(Apologies for posting this as an answer - I don't yet have the required reputation to comment)
Simply adding synchronized to a method doesn't necessarily guarantee thread safety.
How and when is path being populated?
Update after additional information provided
The problem seems to be that the path points are being generated asynchronously, and you are trying to use them before the generation process has finished (or perhaps even started). This happens because the findPathData simply starts the generation process and returns immediately (i.e. before the generation process has finished). In your code, you then go on and build the URL which is supposed to contain the point data immediately. At this point the background point generation process may not have finished, and may not have even started. As a result the point map may be empty or incomplete, and your URL will not be generated as you expect.
You need to find a way to wait until all of the path point data has been returned by the asynchronous processing before creating the URL. This looks like it could be very difficult, if not impossible, with the version of the findPathData method you are using, because it returns points via the callback one at a time and you may not know how many will be generated.
I had a quick look at the API for TMapData and it has a findPathDataAll method which seems to generate all the points and return them in a single callback call rather than one by one. If this is indeed what it does (sorry, I can't read Korean), you could use this method and then generate the URL from the callback, because when it's called you know that the generation process has been completed. If you do this, be careful to make sure that you're on the main thread before interacting with the UI or Activity.
Hope that helps.
i am trying to record and reab back my list into file. It's working great until I restart my application. I am working with simulator (I don't have a real phone under Android)
Here is my function to record my class into a file :
public boolean writeRecordsToFile(String path, DummyContent object){
FileOutputStream fos;
ObjectOutputStream oos = null;
try {
fos = fileContext.openFileOutput(path, Context.MODE_PRIVATE);
oos = new ObjectOutputStream(fos);
oos.writeObject(object);
oos.close();
Log.d("fileManager", "Records write successfully");
return true;
} catch (Exception e) {
Log.e("fileManager", "Cant save records : " + e.getMessage());
return false;
}
finally {
if (oos != null)
try {
oos.close();
} catch (Exception e) {
Log.e("fileManager", "Error while closing stream "+e.getMessage());
}
}
}
Here is my reading Function :
public boolean readRecordsFromFile(String path){
FileInputStream fin;
ObjectInputStream ois=null;
try {
fin = fileContext.openFileInput(path);
ois = new ObjectInputStream(fin);
DummyContent records = (DummyContent) ois.readObject();
records.addItem("test", "test", "test");
ois.close();
Log.d("fileManager", "Records read successfully :\n" + records.toString());
Log.d("fileManager", "nbArticle found : " + String.valueOf(records.ITEMS.size()));
Log.d("fileManager", "article 0 title :\n" + records.ITEMS.get(0).content);
Log.d("fileManager", "article 10 title :\n" + records.ITEMS.get(10).content);
return true;
} catch (Exception e) {
Log.e("fileManager", "Cant read saved records : "+e.getMessage());
return false;
}
finally {
if (ois != null)
try {
ois.close();
} catch (Exception e) {
Log.e("fileManager", "Error in closing stream while reading records : "+e.getMessage());
}
}
}
and here is my class :
public class DummyContent implements Serializable {
/**
* An array of sample (dummy) items.
*/
public static List<DummyItem> ITEMS = new ArrayList<DummyItem>();
/**
* A map of sample (dummy) items, by ID.
*/
public static Map<String, DummyItem> ITEM_MAP = new HashMap<String, DummyItem>();
public void addItem(String first, String second, String third) {
DummyItem dummyItem = new DummyItem(first, second, third, android.R.drawable.ic_input_add);
ITEMS.add(dummyItem);
ITEM_MAP.put(dummyItem.id, dummyItem);
}
public void deleteAll() {
ITEMS = new ArrayList<DummyItem>();
ITEM_MAP = new HashMap<String, DummyItem>();
}
public void changeURL(Long index, String newURL) {
ITEMS.get(index.intValue()).url = newURL;
}
public void changeContent(Long index, String newContent) {
ITEMS.get(index.intValue()).contenu = newContent;
}
/**
* A dummy item representing a piece of content.
*/
public static class DummyItem {
public final String id;
public final String content;
public final String details;
public final int imageResource;
public String url;
public String contenu;
public DummyItem(String id, String content, String details, int imageResource) {
this.id = id;
this.content = content;
this.details = details;
this.imageResource = imageResource;
this.url = "";
this.contenu = "";
}
#Override
public String toString() {
return content;
}
}
}
Finally I read my file at the onCreate of my MainActivity (first activity at the lunching app) :
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
fileManager = new FileManager(this.getApplicationContext());
Log.d("Main", String.valueOf(fileManager.fileExist("Article.art")));
fileManager.readRecordsFromFile("Article.art"); /* Bug here : size of my array is empty but file's size is the same */
}
Here is my console return :
D/fileManager: size = 102
D/fileManager: Records read successfully :
D/fileManager: nbArticle found : 1 (because i add an item at the read
function) E/fileManager: Cant read saved records : Index: 10, Size: 1
I know it is working because when I write and read directly after the writting, I got all my items and I can read several times and I still got all items (this bug semms to be only present when I restart my application)
Maybe can I got help ?
Thanks !
The reason is very easy: You have declared some field as static, which are not covered by standard serialization: So, the contents of these fields were never written nor read from the file. That's why they "dissapeared" after a JVM restart.
Any field you want to be serialized/deserialized, you must declare it as instance member (not static).
See documentation on Serializable.
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
}
}