Download Random Images from file server

Question

This is my attempt. My files are hosted on my own servers mostly JPGs files. I'm trying to download them into my app. I failed to generate those images into my app. I follow the guide from this blog http://getablogger.blogspot.gr/2008/01/android-download-image-from-server-and.html

My xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView 
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello World, HTTPImage load test"
/>
<Button android:id="@+id/get_imagebt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Get an image"
android:layout_gravity="center"
/> 
<ImageView android:id="@+id/imview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
/>
</LinearLayout>

Coding

package com.example.downloadimages;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;




public class MainActivity extends Activity {

    ImageView imView;
    String imageUrl="http://myfilehosting.com/";
    Random r;


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

        r= new Random();

        Button bt3= (Button)findViewById(R.id.get_imagebt);
        bt3.setOnClickListener(getImgListener);
        imView = (ImageView)findViewById(R.id.imview);
    }

    View.OnClickListener getImgListener = new View.OnClickListener()
    {

        public void onClick(View view) {
        // TODO Auto-generated method stub

        //i tried to randomize the file download, in my server i put 4 files with name like
        //jpg0.jpg, jpg1.jpg, jpg2.jpg so different file is downloaded in button press
        int i =r.nextInt()%4;
        downloadFile(imageUrl+i+".jpg");

        }

        Bitmap bmImg;
        void downloadFile(String fileUrl){
        URL myFileUrl =null; 
        try {
        myFileUrl= new URL(fileUrl);
        } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }
        try {
        HttpURLConnection conn= (HttpURLConnection)myFileUrl.openConnection();
        conn.setDoInput(true);
        conn.connect();
        int length = conn.getContentLength();
        int[] bitmapData =new int[length];
        byte[] bitmapData2 =new byte[length];
        InputStream is = conn.getInputStream();

        bmImg = BitmapFactory.decodeStream(is);
        imView.setImageBitmap(bmImg);
        } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }





};
};
}

Answer 1

there are several problems with your code:

• you are trying to perform network operation (download file from remote server) from the UI thread. network operation must be executed from another thread. otherwise - exception been thrown.

one of the ways to launch the code from another thread is:

new Thread(new Runnable() {

        @Override
        public void run() {
            downloadFile(imageUrl+i+".jpg");
        }
    }).start();

better approach would be using AsyncTask or IntentService (which also performing the code on separate thread)

• second thing - you can't just create int array with the size of the input stream: if the image is too big, it can fail. try break the download to segments with fixed size (say 2058 bytes each segment) for example:

  private HttpURLConnection conn;
  private InputStream stream;
  private FileOutputStream out;
  
  private double fileSize;
  private double downloaded;
  
  
  public void downloadFile(String fileURL, String fileName) {
  try {
  
      conn = (HttpURLConnection) new URL(fileURL).openConnection();
      fileSize = conn.getContentLength();
      File file = new File(fileName);
  
      out = new FileOutputStream(file);
      conn.connect();
  
      stream = conn.getInputStream();
  
      while (status == DOWNLOADING) {
          byte buffer[];
  
          if (fileSize - downloaded > MAX_BUFFER_SIZE) {
              buffer = new byte[MAX_BUFFER_SIZE];
          } else {
              buffer = new byte[(int) (fileSize - downloaded)];
          }
          int read = stream.read(buffer);
  
          if (read == -1) {
  
              out.close();
              if (conn != null) {
                  conn.disconnect();
              }
  
              break;
          }
  
          out.write(buffer, 0, read);
          downloaded += read;
      }
  
  } catch (Exception e) {
      Log.e("downloadFile():", e.getMessage());
      if (conn != null) {
          conn.disconnect();
      }
  }
  
  }