Android download and show an image. Show how to use HttpURLConnection and AsyncTask.

activity_main.xml

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

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="showPicture"
        android:text="Show Picture" />

    <ImageView
        android:id="@+id/main_iv_picture"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:scaleType="fitCenter" />
</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.edinstudio.app.training"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="10"
        android:targetSdkVersion="18" />

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

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.edinstudio.app.training.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

MainActivity.java

package com.edinstudio.app.training;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;
import android.widget.Toast;

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

public class MainActivity extends Activity {
    public static final String TAG = "training";

    private ImageView mIvPicture;

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

        mIvPicture = (ImageView) findViewById(R.id.main_iv_picture);
    }

    public void showPicture(View view) {
        ConnectivityManager connectivityManager = (ConnectivityManager)
                getSystemService(CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {
            new DownloadImageAsyncTask()
                    .execute("http://developer.android.com/design/media/principles_delight.png");
        } else {
            Toast.makeText(this, "No network connection available.", Toast.LENGTH_SHORT).show();
        }
    }

    public static Bitmap downloadImageFromUrl(String s) {
        Bitmap bitmap = null;

        try {
            URL url = new URL(s);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000);
            conn.setConnectTimeout(15000);
            conn.setRequestMethod("GET");
            conn.setDoInput(true);

            conn.connect();
            int responseCode = conn.getResponseCode();
            Log.e(TAG, "Response code is " + responseCode);
            bitmap = BitmapFactory.decodeStream(conn.getInputStream());
        } catch (IOException e) {
            Log.e(TAG, e.getMessage());
        }

        return bitmap;
    }

    private class DownloadImageAsyncTask extends AsyncTask<String, Void, Bitmap> {
        @Override
        protected Bitmap doInBackground(String... strings) {
            return downloadImageFromUrl(strings[0]);
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            if (bitmap != null) {
                mIvPicture.setImageBitmap(bitmap);
            } else {
                Log.e(TAG, "In onPostExecute bitmap is null");
            }
        }
    }
}