ANDROID, Parse JSON data from a web server and display on ListView

Question

I am trying to display JSON result from JSON url link. Currently when I load up, it display nothing, just blank page. This is the source where I got information about JSON.

This is my code:

public class DVLAresult extends AppCompatActivity {


    public class DVLAlist extends ListActivity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);
            setContentView(R.layout.content_dvlaresult);


            setListAdapter(new ArrayAdapter(
                    this,android.R.layout.simple_list_item_2,
                    this.populate()));
        }


        private ArrayList<String> populate() {
            ArrayList<String> items = new ArrayList<String>();

            TextView newtext = (TextView) findViewById(R.id.view_number);

            try {
                URL url = new URL
                        ("https://dvlasearch.appspot.com/DvlaSearch?licencePlate=mt09nks&apikey=DvlaSearchDemoAccount");
                HttpURLConnection urlConnection =
                        (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();
                // gets the server json data
                BufferedReader bufferedReader =
                        new BufferedReader(new InputStreamReader(
                                urlConnection.getInputStream()));
                String next;
                while ((next = bufferedReader.readLine()) != null) {
                    JSONArray ja = new JSONArray(next);

                    for (int i = 0; i < ja.length(); i++) {
                        JSONObject jo = (JSONObject) ja.get(i);
                        items.add(jo.getString("text"));
                    }
                }
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return items;
        }
    }
}

And this is my XML file simple_list_2.xml

<?xml version="1.0" encoding="utf-8"?>

<TwoLineListItem xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:minHeight="?attr/listPreferredItemHeight"
    android:mode="twoLine"
    android:paddingStart="?attr/listPreferredItemPaddingStart"
    android:paddingEnd="?attr/listPreferredItemPaddingEnd">

    <TextView android:id="@id/text1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:textAppearance="?attr/textAppearanceListItem" />

    <TextView android:id="@id/text2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/text1"
        android:layout_alignStart="@id/text1"
        android:textAppearance="?attr/textAppearanceListItemSecondary" />

    <TextView android:id="@id/text3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/text2"
        android:layout_alignStart="@id/text2"
        android:textAppearance="?attr/textAppearanceListItemSecondary" />

... Continue up to text18, because I have 18 fields.

</TwoLineListItem>

And this is main XML ListView

 <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/list"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_above="@+id/button2"
        android:layout_below="@+id/view_number" />

You can't make a request on the same Thread as general Thread. Use a class who `extends Asynctask` or use a library like Retrofit, Volley, etc.. — Raphael Teyssandier, Mar 25 '16 at 14:28
Request will be done from main activity and this is second activity. So I will set a value and will change URL according to this value. But currently no result want to be displayed. I will update my question and I will put a source where I have got information abut JSON — , Mar 25 '16 at 14:31
Arent you getting an Exception? It looks like you are doing a network connection in the main Thread... anyway if u have problems like that, you should print debug messages every step in your code (Log.i ("json", "calling method populate()")). This will help you finding the tricky part. You should always print the results from things like the URL connection to ensure you got valid responses. — Luftbaum, Mar 25 '16 at 14:33
@J.FOG. Are you sure you are getting a response back from the server. I am not a expert, but I recently did some related work, and I should able to get the data to display in a scroll view with out much difficult. — Mahendra Gunawardena, Mar 27 '16 at 00:57

Mahendra Gunawardena · Accepted Answer · 2016-05-01T01:47:18.303

I happen to encounter similar problem. Here is the code that help me find resolution. Hope this will help you.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="SEND GET REQUEST"
        android:id="@+id/sendGet"
        android:onClick="sendGetRequest"
        android:layout_alignParentStart="true" />

    <ScrollView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/scrollView"
        android:layout_below="@+id/sendGet"
        android:layout_centerHorizontal="true">

        <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Response ....."
            android:id="@+id/showOutput"
            android:layout_alignEnd="@+id/scrollView"
            android:layout_marginEnd="34dp" />

    </ScrollView>

</RelativeLayout>

MainActivity.java

import android.app.ProgressDialog;
import android.content.Context;
import android.net.Uri;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import com.google.android.gms.appindexing.Action;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    private ProgressDialog progress;
    /**
     * ATTENTION: This was auto-generated to implement the App Indexing API.
     * See https://g.co/AppIndexing/AndroidStudio for more information.
     */
 //   private GoogleApiClient client;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
  //      client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
    }

    public void sendGetRequest(View View) {
        new GetClass(this).execute();
    }

    @Override
    public void onStart() {
        super.onStart();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
 //       client.connect();
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "Main Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app deep link URI is correct.
                Uri.parse("android-app://com.example.gunawardena.get_post_demo/http/host/path")
        );
 //       AppIndex.AppIndexApi.start(client, viewAction);
    }

    @Override
    public void onStop() {
        super.onStop();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "Main Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app deep link URI is correct.
                Uri.parse("android-app://com.example.gunawardena.get_post_demo/http/host/path")
        );
      //  AppIndex.AppIndexApi.end(client, viewAction);
      // client.disconnect();
    }

    private class GetClass extends AsyncTask<String, Void, Void> {

        private final Context context;

        public GetClass(Context c) {
            this.context = c;
        }

        protected void onPreExecute() {
            progress = new ProgressDialog(this.context);
            progress.setMessage("Loading Get Method.....");
            progress.show();
        }

        @Override
        protected Void doInBackground(String... params) {
            try {

                final TextView outputView = (TextView) findViewById(R.id.showOutput);
                URL url = new URL("https://dvlasearch.appspot.com/DvlaSearch?licencePlate=mt09nks&apikey=DvlaSearchDemoAccount");
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();

                connection.setRequestMethod("GET");
                connection.setRequestProperty("USER-AGENT", "Mozilla/5.0");
                connection.setRequestProperty("ACCEPT-LANGUAGE", "en-US,en;0.5");

                int responseCode = connection.getResponseCode();

                final StringBuilder output = new StringBuilder("Request URL " + url);
                output.append(System.getProperty("line.separator") + "Response Code " + responseCode);
                output.append(System.getProperty("line.separator") + "Type " + "GET");
                BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String line = "";
                StringBuilder responseOutput = new StringBuilder();
                System.out.println("output===============" + br);
                while ((line = br.readLine()) != null) {
                    responseOutput.append(line);
                }
                br.close();

                output.append(System.getProperty("line.separator") + "Response " + System.getProperty("line.separator") + System.getProperty("line.separator") + responseOutput.toString());

                MainActivity.this.runOnUiThread(new Runnable() {

                    @Override
                    public void run() {
                        outputView.setText(output);
                        progress.dismiss();

                    }
                });

            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return null;
        }
    }
}

Output on the Emulator

HTH

References:

Let me know if this help and if you any question parsing the JSON data. — Mahendra Gunawardena, Mar 27 '16 at 03:04

ANDROID, Parse JSON data from a web server and display on ListView

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