Android Restful web services tutorial

In this tutorial, we are going to integrate android with restful web services which return json as response.
So we are going to get json from restful web services and then render json response to android custom listview.

Example :

I have already implemented restful webservices json example. I am going to use same example for implementation of restful web services.
If you are going to deploy above web service then use below url to fetch json data
http://192.168.2.22:8080/JAXRSJsonExample/rest/countries
Here 192.168.2.22 is IP address of my machine. Once you implement this web services on your machine, you should replace it with your ip address.
If you don't want to implement rest web service yourself and want below json response. You can use below link.
https://cdn.rawgit.com/arpitmandliya/AndroidRestJSONExample/master/countries.json
You will get below Json response from above URL:
[  
   {  
      "id":1,
      "countryName":"India"
   },
   {  
      "id":4,
      "countryName":"China"
   },
   {  
      "id":3,
      "countryName":"Nepal"
   },
   {  
      "id":2,
      "countryName":"Bhutan"
   }
]
We are getting above Json array from rest web service. If you are not familiar with JSON, you can go through Json tutorial. We are going to render above JSON response to android custom listview as below:

Lets code this example now:

Source code:

Step 1 :Creating Project

Create an android application project named "AndroidRestJsonExample".

Step 2 : Creating Layout

Change res ->layout -> activity_main.xml as below:
<?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:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="10dp"
    tools:context="com.java2blog.androidrestjsonexample.MainActivity">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Fetching countries data"
        android:id="@+id/btnSubmit"
        />

    <ListView
        android:id="@+id/android:list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/btnSubmit"
        />
</RelativeLayout>

We have one button and listview. When you click the button, we are going to populate data in listview by calling restful web services and render it on the listview.

Step 3: Creating layout for Row

As We have declared ListView widget in activity_main.xml. Now we need to provide layout for individual row.
  • Go to res -> layout
  • right click on layout
  • Click on New -> File. 
  • Create a file named "row_item.xml" and paste below code in row_item.xml.
<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_columnWeight="1"
        android:layout_marginLeft="10dp"
        android:textSize="30dp"
        android:textColor="#1E90FF"
        android:id="@+id/textViewId"
        android:layout_row="0"
        android:layout_column="1" />
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_columnWeight="1"
        android:layout_marginLeft="10dp"
        android:textSize="20dp"
        android:textColor="#4B0082"
        android:id="@+id/textViewCountry"
        android:layout_row="1"
        android:layout_column="1" />
</GridLayout>

Step 4 : Creating model object Country :

If you notice, we are getting Json array from restful web service which has 4 items. Each item have two attributes id and countryName. We are going to create country object for each item.
package com.java2blog.androidrestjsonexample;
public class Country{
    int id;
    String countryName;

    public Country(int i, String countryName) {
        super();
        this.id = i;
        this.countryName = countryName;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getCountryName() {
        return countryName;
    }
    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }
}

Step 5 :  Creating BaseAdapter for ListView

Before creating MainActivity, we need to create CustomCountryList class for custom ListView row.
package com.java2blog.androidrestjsonexample;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import com.java2blog.androidrestjsonexample.Country;
import com.java2blog.androidrestjsonexample.R;

import java.util.ArrayList;

public class CustomCountryList extends BaseAdapter {


    private Activity context;
    ArrayList<Country> countries;


    public CustomCountryList(Activity context, ArrayList<Country> countries) {
     //   super(context, R.layout.row_item, countries);
        this.context = context;
        this.countries=countries;

    }

    public static class ViewHolder
    {
        TextView textViewId;
        TextView textViewCountry;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View row=convertView;

        LayoutInflater inflater = context.getLayoutInflater();
        ViewHolder vh;
        if(convertView==null) {
            vh=new ViewHolder();
            row = inflater.inflate(R.layout.row_item, null, true);
            vh.textViewId = (TextView) row.findViewById(R.id.textViewId);
            vh.textViewCountry = (TextView) row.findViewById(R.id.textViewCountry);
            // store the holder with the view.
            row.setTag(vh);
        }
        else {
            vh = (ViewHolder) convertView.getTag();
        }

        vh.textViewCountry.setText(countries.get(position).getCountryName());
        vh.textViewId.setText(""+countries.get(position).getId());

        return  row;
    }

    public long getItemId(int position) {
        return position;
    }

    public Object getItem(int position) {
        return position;
    }

    public int getCount() {

        if(countries.size()<=0)
            return 1;
        return countries.size();
    }
}
This class is used to populating data for ListVIew. getView method is get called for drawing each row.

Step 6 : Creating MainActivity

We are going to create a addition inner class GetServerData which extends AsyncTask. This class will make https call in background thread.
Here are three methods which you may need to implement while using AsyncTask.
  • onPreExecute() : This method will get called before making HTTP call. We are initializing ProgressDialog here.
  • doInBackground : We are going to make HTTP call in this method. We have use HttpURLConnection class to make HTTP call. You can not access any UI elements while executing this method
  • onPostExecute  : This executes after execution of doInBackground method. In this method, we are going to create CustomCountryList object and populate listview data.
Change src/main/packageName/MainActivity.java as below:
package com.java2blog.androidrestjsonexample;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.StrictMode;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;

import javax.net.ssl.HttpsURLConnection;

import static android.content.ContentValues.TAG;

public class MainActivity extends AppCompatActivity {

    private Button btnSubmit;
    String responseText;
    StringBuffer response;
    URL url;
    Activity activity;
    ArrayList<Country> countries=new ArrayList<Country>();
    private ProgressDialog progressDialog;
    ListView listView;
    // In case if you deploy rest web service, then use below link and replace below ip address with yours
    //http://192.168.2.22:8080/JAXRSJsonExample/rest/countries
    
    //Direct Web services URL
    private String path = "https://cdn.rawgit.com/arpitmandliya/AndroidRestJSONExample/master/countries.json";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            activity = this;
            btnSubmit = (Button) findViewById(R.id.btnSubmit);
            listView = (ListView) findViewById(android.R.id.list);
            btnSubmit.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    countries.clear();
                    //Call WebService
                    new GetServerData().execute();
                }
            });
        }

        class GetServerData extends AsyncTask
        {

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                // Showing progress dialog
                progressDialog = new ProgressDialog(MainActivity.this);
                progressDialog.setMessage("Fetching conntry data");
                progressDialog.setCancelable(false);
                progressDialog.show();

            }

            @Override
            protected Object doInBackground(Object[] objects) {
                return getWebServiceResponseData();
            }

            @Override
            protected void onPostExecute(Object o) {
                super.onPostExecute(o);

                // Dismiss the progress dialog
                if (progressDialog.isShowing())
                    progressDialog.dismiss();
                // For populating list data
                CustomCountryList customCountryList = new CustomCountryList(activity, countries);
                listView.setAdapter(customCountryList);

                listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                        Toast.makeText(getApplicationContext(),"You Selected "+countries.get(position).getCountryName()+ " as Country",Toast.LENGTH_SHORT).show();        }
                });
            }
        }
        protected Void getWebServiceResponseData() {

            try {

                url = new URL(path);
                Log.d(TAG, "ServerData: " + path);
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setReadTimeout(15000);
                conn.setConnectTimeout(15000);
                conn.setRequestMethod("GET");

                int responseCode = conn.getResponseCode();

                Log.d(TAG, "Response code: " + responseCode);
                if (responseCode == HttpsURLConnection.HTTP_OK) {
                    // Reading response from input Stream
                    BufferedReader in = new BufferedReader(
                            new InputStreamReader(conn.getInputStream()));
                    String output;
                    response = new StringBuffer();

                    while ((output = in.readLine()) != null) {
                        response.append(output);
                    }
                    in.close();
                }}
             catch(Exception e){
                    e.printStackTrace();
            }

                responseText = response.toString();
                //Call ServerData() method to call webservice and store result in response
              //  response = service.ServerData(path, postDataParams);
                Log.d(TAG, "data:" + responseText);
                try {
                    JSONArray jsonarray = new JSONArray(responseText);
                    for (int i = 0; i < jsonarray.length(); i++) {
                        JSONObject jsonobject = jsonarray.getJSONObject(i);
                        int id = jsonobject.getInt("id");
                        String country = jsonobject.getString("countryName");
                        Log.d(TAG, "id:" + id);
                        Log.d(TAG, "country:" + country);
                        Country countryObj=new Country(id,country);
                        countries.add(countryObj);
                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                }
                return null;
            }
    }

Step 7: Add internet permission in AndroidManifest.xml

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

Put it in AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.java2blog.androidrestjsonexample">

    <uses-permission android:name="android.permission.INTERNET" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>
Done, we have added internet permission to AndroidManifest.xml. Your application must be able to access internet now.

Step 8 : Running the app 

When you run the app, you will get below screen:


When you click on above button, you will get below screen.


We are done with Android Restful web services json example. If you are facing any issue, please comment.

Written by Arpit:

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