Develop Reference

Downloading a JSON Array from a URL in Android

I'm trying to download a JSON file in this format
[
{
"CRN":"10001",
"Course":"REG1"
},
{
"CRN":"10002",
"Course":"REG2"
}
]
I understand how to use a JSONArray class once it is created but I don't know how to create the JSONArray object from the file. If the URL location of the file were to be "www.test.com" how would I go about downloading it in background upon the launch of my application so as to not interfere with the launching of the app but not require the user to manually download it themselves.

You might want to check out this helpful library: Retrofit
It makes grabbing and parsing JSON data easy!

I think you should look for Android Web Service example. Where you can find info about
1.How to make a HTTP request to server (using URL eg. www.google.com)
2. How to handle Response from Server
3. How to parse JSON/XML response from Server etc.
Here is the Simple Tutorial I Found for you.
Android Web service for Log-in and Registration
Just go through step by step.
In the example we are making request to server for login and getting response then going ahead in app.
Here is the code snipp.
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) {
// Making HTTP request
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "n");
}
is.close();
json = sb.toString();
Log.e("JSON", json);
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}

A good way to download the JSON file automatically, would be to launch an AsyncTask during your onCreate method of the home activity.
JSON files are nothing more than text files in a special format, so the could be easily downloaded as a response from a HttpURLConnection, and then be treated as a String.
A suggestion for parsing the JSON objets into Java objects would be the Jackson JSON Processor. You could use the class ObjectMapper of this library to automatically create the objects.
If you are planing to implement the server side by yourself, and you also need a library to send JSON objects, you could use Jersey on both server and client.

json to android could not connect to database

i'm trying to parse the information of a json array into android.
I use the below code, and i get info from a webservice, if i open the php file it's all ok, but in android i get could not connect to database. I do have set permissions to access the internet...
Here is the code i use:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
StrictMode.enableDefaults(); //STRICT MODE ENABLED
resultView = (TextView) findViewById(R.id.result);
getData();
}
public void getData(){
String result = "";
InputStream isr = null;
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://192.168.10.28/albana/getAllCustomers.php"); //YOUR PHP SCRIPT ADDRESS
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
isr = entity.getContent();
}
catch(Exception e){
Log.e("log_tag", "Error in http connection "+e.toString());
resultView.setText("Couldnt connect to database");
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(isr,"iso-8859-1"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
isr.close();
result=sb.toString();
}
catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
//parse json data
try {
String s = "";
JSONArray jArray = new JSONArray(result);
for(int i=0; i<jArray.length();i++){
JSONObject json = jArray.getJSONObject(i);
s = s +
"Name : "+json.getString("FirstName")+" "+json.getString("LastName")+"\n"+
"Age : "+json.getInt("Age")+"\n"+
"Mobile Using : "+json.getString("Mobile")+"\n\n";
}
resultView.setText(s);
} catch (Exception e) {
// TODO: handle exception
Log.e("log_tag", "Error Parsing Data "+e.toString());
}
}
I get the message "Could not connect to database";
No errors on the Log Cat...
Please someone suggest me..

You are trying to connect to 192.168.10.28, which is a private or non-routable network address. You can only connect to it if you're on that network (or a network that specifically connects to it). Are you connected through wifi to the network? If so, I would expect it to work so try opening the URL in your web browser and see if you get a json response. If you're connected to it by your mobile network I wouldn't expect it to work.

I'm pretty sure you don't want to use a HttpPost here. Try HttpGet instead, syntax stays the same.
Also check Dave's answer.

In httpd.conf file make the following changes
change:
Deny from all
Allow from 127.0.0.1
Allow from ::1
Allow from localhost
to:
Allow from all
and restart all the services, works like a charm.

android: create json object or array?

I'm learning everyday a little bit more about android developing and json code.
But now I'm stuck on this;
I can get my values from my online database and show it but I see the entire json code.
And I would like to see just the part I want it to show.
this is my code, I think it's really basic but i'm also learning :)
As you can see I'm just getting the value from the webpage and putting it in my textview, but I would like to put it in a JSONObject or JSONArray don't know witch one is better.
can somebody please assist me with this?
With kind regards
public class Bordje extends Activity{
public void onCreate (Bundle savedInstanceState) {
try
{
super.onCreate(savedInstanceState);
setContentView(R.layout.bordje);
//This is out textview element, obtained by id from XML Layout
TextView myListView = (TextView)findViewById(R.id.netResult2);
//Lets connect to the internet
try {
String result = "";
//create new client object
HttpClient httpclient = new DefaultHttpClient();
//now post to the url
HttpPost httppost = new HttpPost("http://www.wvvzondag2.nl/android/leesbordje.php");
//execute url
HttpResponse response = httpclient.execute(httppost);
//get message from the response
HttpEntity entity = response.getEntity();
//get the content from message
InputStream webs = entity.getContent();
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(webs, "iso-8859-1"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
//slow our inputstream
webs.close();
//puts the resut into a string
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
//Parsing the JSON Data
try{
JSONArray jArray = new JSONArray(result);
for(int i=0;i<jArray.length();i++){
JSONObject json_data = jArray.getJSONObject(i);
json_data.getString("introtext");
//Get an output to the screen
//then here should be some code that displays text?
//myListView.setText(Html.fromHtml(json_data)); ?
}
}catch(JSONException e){
Log.e("log_tag", "Error parsing data "+e.toString());
}
}catch(Exception e){
Log.e("log_tag", "Error in http connection"+e.toString());
}
}
catch (Exception e)
{
//this is the line of code that sends a real error message to the log
Log.e("ERROR", "ERROR IN CODE: " + e.toString());
}
}

It's not really a question of which one is better. A JSON object and JSON array are two different things.
A JSON Array is an ordered sequence of (like) items (http://www.json.org/javadoc/org/json/JSONArray.html).
JSONArray jsonArray = new JSONArray("[JSON TEXT]");
String textToDisplay = jsonArray.getString(index); //return String at index
A JSON Object is a map (http://www.json.org/javadoc/org/json/JSONObject.html).
JSONObject jsonObj = new JSONObject("[JSON TEXT]");
String textToDisplay = jsonObj.getString("key"); //returns String value
Then after you have the data, set it in the text view like before.
myListView.setText(textToDisplay);

If you are getting valid json from server you can simply make a JSONArray or JSONObject of it depending on whose object you are getting so there is no point of saying which one is better. However in your case it will most probably be a JSONArray.
Well to achieve that you can use gson to convert a valid json string into JSONObject or JSONArray.
you will be working with .toJson() and .fromJSON(object) methods.

Android parse json from url and store it

Hi there i'm creating my first android app and i'm wanting to know what is the best and most efficient way of parsing a JSON Feed from a URL.Also Ideally i want to store it somewhere so i can keep going back to it in different parts of the app. I have looked everywhere and found lots of different ways of doing it and i'm not sure which to go for. In your opinion whats the best way of parsing json efficiently and easily?

I'd side with whatsthebeef on this one, grab the data and then serialize to disk.
The code below shows the first stage, grabbing and parsing your JSON into a JSON Object and saving to disk
// Create a new HTTP Client
DefaultHttpClient defaultClient = new DefaultHttpClient();
// Setup the get request
HttpGet httpGetRequest = new HttpGet("http://example.json");
// Execute the request in the client
HttpResponse httpResponse = defaultClient.execute(httpGetRequest);
// Grab the response
BufferedReader reader = new BufferedReader(new InputStreamReader(httpResponse.getEntity().getContent(), "UTF-8"));
String json = reader.readLine();
// Instantiate a JSON object from the request response
JSONObject jsonObject = new JSONObject(json);
// Save the JSONOvject
ObjectOutput out = new ObjectOutputStream(new FileOutputStream(new File(getCacheDir(),"")+"cacheFile.srl"));
out.writeObject( jsonObject );
out.close();
Once you have the JSONObject serialized and save to disk, you can load it back in any time using:
// Load in an object
ObjectInputStream in = new ObjectInputStream(new FileInputStream(new File(new File(getCacheDir(),"")+"cacheFile.srl")));
JSONObject jsonObject = (JSONObject) in.readObject();
in.close();

Your best bet is probably GSON
It's simple, very fast, easy to serialize and deserialize between json objects and POJO, customizable, although generally it's not necessary and it is set to appear in the ADK soon. In the meantime you can just import it into your app. There are other libraries out there but this is almost certainly the best place to start for someone new to android and json processing and for that matter just about everyone else.
If you want to persist you data so you don't have to download it every time you need it, you can deserialize your json into a java object (using GSON) and use ORMLite to simply push your objects into a sqlite database. Alternatively you can save your json objects to a file (perhaps in the cache directory)and then use GSON as the ORM.

This is pretty straightforward example using a listview to display the data. I use very similar code to display data but I have a custom adapter. If you are just using text and data it would work fine. If you want something more robust you can use lazy loader/image manager for images.

Since an http request is time consuming, using an async task will be the best idea. Otherwise the main thread may throw errors. The class shown below can do the download asynchronously
private class jsonLoad extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... urls) {
String response = "";
for (String url : urls) {
DefaultHttpClient client = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
try {
HttpResponse execute = client.execute(httpGet);
InputStream content = execute.getEntity().getContent();
BufferedReader buffer = new BufferedReader(new InputStreamReader(content));
String s = "";
while ((s = buffer.readLine()) != null) {
response += s;
}
} catch (Exception e) {
e.printStackTrace();
}
}
return response;
}
#Override
protected void onPostExecute(String result) {
// Instantiate a JSON object from the request response
try {
JSONObject jsonObject = new JSONObject(result);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
File file = new File(getApplicationContext().getFilesDir(),"nowList.cache");
try {
file.createNewFile();
FileOutputStream writer = openFileOutput(file.getName(), Context.MODE_PRIVATE);
writer.write(result);
writer.flush();
writer.close();
}
catch (IOException e) { e.printStackTrace(); return false; }
}
}
Unlike the other answer, here the downloaded json string itself is saved in file. So Serialization is not necessary
Now loading the json from url can be done by calling
jsonLoad jtask=new jsonLoad ();
jtask.doInBackground("http:www.json.com/urJsonFile.json");
this will save the contents to the file.
To open the saved json string
File file = new File(getApplicationContext().getFilesDir(),"nowList.cache");
StringBuilder text = new StringBuilder();
try {
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null) {
text.append(line);
text.append('\n');
}
br.close();
}
catch (IOException e) {
//print log
}
JSONObject jsonObject = new JSONObject(text);

Updateing Android application content via internet?

i want to develop an Android application that will take the content from internet (server) and present it in the application.
(ex. i take the todays weather forecast, put the numbers in SQLite database or .txt file , put the database/txt file on internet server so when i open the application, the app connects&downloads the database via the net and presents me with todays forecast)
If you can references me to some example/video tutorial/book that deals with this issue i will be very thankful!

What you want to do is developing a rest api that provides data for your android app. E.g. you website has some content that you want use in your app, then you could write a php script that just returns that data in a specific format.
E.g. mysite.net/rest/fetchAllLocations.php?maybe_some_parameters
This would return locations in e.g. json format, here is an example how that looks like:
[{"id":1,"shop_lng":8.5317153930664,"shop_lat":52.024803161621,"shop_zipcode":33602,"shop_city":"Bielefeld","shop_street":"Arndtstra\u00dfe","shop_snumber":3,"shop_name":"M\u00fcller","shop_desc":"Kaufhaus"}]
Here is an example for a rest api request:
http://shoqproject.supervisionbielefeld.de/public/gateway/gateway/get-shops-by-city/city/Bielefeld
So when you have your rest api set up you can deal with receiving that data with your android phone. I use a static method to get this data:
public class JsonGrabber{
public static JSONArray receiveData(){
String url = "your url";
String result = "";
DefaultHttpClient client = new DefaultHttpClient();
HttpGet method = new HttpGet(url);
HttpResponse res = null;
try {
res = client.execute(method);
} catch (ClientProtocolException e1) {
e1.printStackTrace();
} catch (IOException e1) {
e1.printStackTrace();
}
try{
InputStream is = res.getEntity().getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"));
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
JSONArray jArray = null;
try{
jArray = new JSONArray(result);
}catch(JSONException e){
Log.e("log_tag", "Error parsing data "+e.toString());
}
return jArray;
}
}
Well thats all, once you have your data in json format you just have to parse it:
JSONArray test = (JSONArray) JsonGrabber.receiveData()
try {
for(int i=0;i<test.length();i++){
JSONObject json_data = test.getJSONObject(i);
int id = json_data.getInt("id");
}
}
The web request should run in another thread, because it can be a time consuming process. So you need to deal with AsyncTask. Here are some resources:
Painless Threading
Multithreading for performance
Hello Android Tutorial