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" />

Answer 1

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:

• How to send HTTP request GET/POST in Java
• Java HttpURLConnection Example to send HTTP GET/POST Requests
• Android POST and GET Request using HttpURLConnection Tutorial