Android Development – Parsing JSON Data from a URL

Date Posted: December 21, 2015, 6:00 am


JSON is very light weight, structured, easy to parse and much human readable. JSON is best alternative to XML when your android app needs to interchange data with your server. In this simple tutorial I am going to show you how to parse a JSON response from a URL and display it in a ListView

Before we start

  • Make sure you have properly setup the Android SDK, AVD for Testing the Application.
  • Create a New project in Android Studio / Eclipse IDE with the package as “com.carlofontanos.parsejsondatafromurl“. Create the Main Activity as “MainActivity” and the main Layout as “activity_main”.

For this example, the JSON data we are going to parse can be found here: http://carlofontanos.com/api/tutorials.php?data=all

MainActivity.java

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package com.carlofontanos.parsejsondatafromurl;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;

import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends AppCompatActivity {

    ListView listView;
    ArrayList<String> tutorialList = new ArrayList<String>();

    private final static String URL = "http://carlofontanos.com/api/tutorials.php?data=all";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        new FetchDataTask().execute(URL);

    }

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

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

            InputStream inputStream = null;
            String result= null;
            HttpClient client = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(params[0]);

            try {

                HttpResponse response = client.execute(httpGet);
                inputStream = response.getEntity().getContent();

                // convert inputstream to string
                if(inputStream != null){
                    result = convertInputStreamToString(inputStream);
                    Log.i("App", "Data received:" +result);

                }
                else
                    result = "Failed to fetch data";

                return result;

            } catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPostExecute(String dataFetched) {
            //parse the JSON data and then display
            parseJSON(dataFetched);
        }


        private String convertInputStreamToString(InputStream inputStream) throws IOException{
            BufferedReader bufferedReader = new BufferedReader( new InputStreamReader(inputStream));
            String line = "";
            String result = "";
            while((line = bufferedReader.readLine()) != null)
                result += line;

            inputStream.close();
            return result;

        }

        private void parseJSON(String data){

            try{
                JSONArray jsonMainNode = new JSONArray(data);

                int jsonArrLength = jsonMainNode.length();

                for(int i=0; i < jsonArrLength; i++) {
                    JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);
                    String postTitle = jsonChildNode.getString("post_title");
                    tutorialList.add(postTitle);
                }

                // Get ListView object from xml
                listView = (ListView) findViewById(R.id.list);

                // Define a new Adapter
                ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, android.R.id.text1, tutorialList);

                // Assign adapter to ListView
                listView.setAdapter(adapter);

            }catch(Exception e){
                Log.i("App", "Error parsing data" +e.getMessage());

            }
        }
    }
}

actvitiy_main.xml

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<?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"
   tools:context="${relativePackage}.${activityClass}" >

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:orientation="vertical" >

        <ListView
           android:id="@+id/list"
           android:textColor="#000000"
           android:layout_height="wrap_content"
           android:layout_width="match_parent">
        </ListView>

    </LinearLayout>

</RelativeLayout>

Android recently made a variety of system changes and API behavior changes, they have removed the built in HTTPClient due to security reasons, but you can still use it by downloading the latest HTTPClient library from here https://hc.apache.org/downloads.cgi – include the jar files into your app/libs folder then add the following dependency into your gradle file:

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dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
}

You might also get a META-INF error when running the app, to fix that simply include the following packing options in your gradle file:

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android {
    packagingOptions {
        exclude 'META-INF/DEPENDENCIES'
        exclude 'META-INF/LICENSE'
        exclude 'META-INF/LICENSE.txt'
        exclude 'META-INF/license.txt'
        exclude 'META-INF/NOTICE'
        exclude 'META-INF/NOTICE.txt'
        exclude 'META-INF/notice.txt'
        exclude 'META-INF/ASL2.0'
    }
}

As we are fetching the JSON by making HTTP calls, we need to add INTERNET permission in our AndroidManifest.xml file. Open AndroidManifest.xml and add the following permission.

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<uses-permission android:name="android.permission.INTERNET" />

Run the Program

Everything’s set, now it’s time to run your program! You should be able to see a ListView similar to the screenshot bellow:

simple-android-app-that-queries-data-from-a-url-then-displays-it-to-the-screen

About author


Carl Victor Fontanos

A fine gentleman specializing in front-end and back-end development with extensive experience building high performance web applications that keeps users engaged and help businesses grow.

 
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