Le Tutoriel de Android Networking

private boolean checkInternetConnection() {
  
      ConnectivityManager connManager =
              (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);

    
      NetworkInfo networkInfo = connManager.getActiveNetworkInfo();

      if (networkInfo == null) {
          Toast.makeText(this, "No default network is currently active", Toast.LENGTH_LONG).show();
          return false;
      }

      if (!networkInfo.isConnected()) {
          Toast.makeText(this, "Network is not connected", Toast.LENGTH_LONG).show();
          return false;
      }

      if (!networkInfo.isAvailable()) {
          Toast.makeText(this, "Network not available", Toast.LENGTH_LONG).show();
          return false;
      }
      Toast.makeText(this, "Network OK", Toast.LENGTH_LONG).show();
      return true;
  }

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();

StrictMode.setThreadPolicy(policy);

package org.o7planning.androidnetworkingdemo;

import java.io.InputStream;
import java.io.Reader;

public class IOUtils {

    public static void closeQuietly(InputStream in)  {
        try {
            in.close();
        }catch (Exception e) {

        }
    }

    public static void closeQuietly(Reader reader)  {
        try {
            reader.close();
        }catch (Exception e) {

        }
    }

}

package org.o7planning.androidnetworkingdemo;

import android.os.AsyncTask;
import android.util.Log;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

// A task with String input parameter, and returns the result as String.
public class DownloadJsonTask
        // AsyncTask<Params, Progress, Result>
        extends AsyncTask<String, Void, String> {

    private TextView textView;

    public DownloadJsonTask(TextView textView)  {
        this.textView= textView;
    }

    @Override
    protected String doInBackground(String... params) {
        String textUrl = params[0];

        InputStream in = null;
        BufferedReader br= null;
        try {
            URL url = new URL(textUrl);
            HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();

            httpConn.setAllowUserInteraction(false);
            httpConn.setInstanceFollowRedirects(true);
            httpConn.setRequestMethod("GET");
            httpConn.connect();
            int resCode = httpConn.getResponseCode();

            if (resCode == HttpURLConnection.HTTP_OK) {
                in = httpConn.getInputStream();
                br= new BufferedReader(new InputStreamReader(in));

                StringBuilder sb= new StringBuilder();
                String s= null;
                while((s= br.readLine())!= null) {
                    sb.append(s);
                    sb.append("\n");
                }
                return sb.toString();
            } else {
                return null;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            IOUtils.closeQuietly(in);
            IOUtils.closeQuietly(br);
        }
        return null;
    }

    // When the task is completed, this method will be called
    // Download complete. Lets update UI
    @Override
    protected void onPostExecute(String result) {
        if(result  != null){
            this.textView.setText(result);
        } else{
            Log.e("MyMessage", "Failed to fetch data!");
        }
    }
}

package org.o7planning.androidnetworkingdemo;


import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.ImageView;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

// A task with String input parameter, and returns the result as bitmap.
public class DownloadImageTask
        // AsyncTask<Params, Progress, Result>
        extends AsyncTask<String, Void, Bitmap> {

    private ImageView imageView;

    public DownloadImageTask(ImageView imageView)  {
        this.imageView= imageView;
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        String imageUrl = params[0];

        InputStream in = null;
        try {
            URL url = new URL(imageUrl);
            HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();

            httpConn.setAllowUserInteraction(false);
            httpConn.setInstanceFollowRedirects(true);
            httpConn.setRequestMethod("GET");
            httpConn.connect();
            int resCode = httpConn.getResponseCode();

            if (resCode == HttpURLConnection.HTTP_OK) {
                in = httpConn.getInputStream();
            } else {
                return null;
            }

            Bitmap bitmap = BitmapFactory.decodeStream(in);
            return bitmap;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            IOUtils.closeQuietly(in);
        }
        return null;
    }

    // When the task is completed, this method will be called
    // Download complete. Lets update UI
    @Override
    protected void onPostExecute(Bitmap result) {
        if(result  != null){
            this.imageView.setImageBitmap(result);
        } else{
            Log.e("MyMessage", "Failed to fetch data!");
        }
    }
}

package org.o7planning.androidnetworkingdemo;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private ImageView imageView;
    private TextView textView;
    private Button buttonImg;
    private Button buttonJson;

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

        this.imageView = (ImageView) this.findViewById(R.id.imageView);
        this.textView = (TextView) this.findViewById(R.id.textView);
        this.buttonImg = (Button) this.findViewById(R.id.button_img);
        this.buttonJson = (Button) this.findViewById(R.id.button_json);

        this.buttonImg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadAndShowImage(v);
            }
        });
        this.buttonJson.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadAndShowJson(v);
            }
        });
    }


    private boolean checkInternetConnection() {
        // Get Connectivity Manager
        ConnectivityManager connManager =
                (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);

        // Details about the currently active default data network
        NetworkInfo networkInfo = connManager.getActiveNetworkInfo();

        if (networkInfo == null) {
            Toast.makeText(this, "No default network is currently active", Toast.LENGTH_LONG).show();
            return false;
        }

        if (!networkInfo.isConnected()) {
            Toast.makeText(this, "Network is not connected", Toast.LENGTH_LONG).show();
            return false;
        }

        if (!networkInfo.isAvailable()) {
            Toast.makeText(this, "Network not available", Toast.LENGTH_LONG).show();
            return false;
        }
        Toast.makeText(this, "Network OK", Toast.LENGTH_LONG).show();
        return true;
    }

    // When user click on the "Download Image".
    public void downloadAndShowImage(View view) {
        boolean networkOK = this.checkInternetConnection();
        if (!networkOK) {
            return;
        }
        String imageUrl = "https://o7planning.org/download/static/default/demo-data/logo.png";

        // Create a task to download and display image.
        DownloadImageTask task = new DownloadImageTask(this.imageView);

        // Execute task (Pass imageUrl).
        task.execute(imageUrl);
    }

    // When user click on the "Download Json".
    public void downloadAndShowJson(View view) {
        boolean networkOK = this.checkInternetConnection();
        if (!networkOK) {
            return;
        }
        String jsonUrl = "https://o7planning.org/download/static/default/demo-data/company.json";

        // Create a task to download and display json content.
        DownloadJsonTask task = new DownloadJsonTask(this.textView);

        // Execute task (Pass jsonUrl).
        task.execute(jsonUrl);
    }


}