Android实现多线程下载图片的方法

 static Bitmap downloadBitmapByCwj(String url) { 
 final AndroidHttpClient client = AndroidHttpClient.newInstance("Android123"); 
 final HttpGet getRequest = new HttpGet(url); 

 try { 
  HttpResponse response = client.execute(getRequest); 
  final int statusCode = response.getStatusLine().getStatusCode(); 
  if (statusCode != HttpStatus.SC_OK) { 
   Log.e("cwjDebug", "Error " + statusCode + " while retrieving bitmap from " + url); 
   return null; 
  } 
   
  final HttpEntity entity = response.getEntity(); 
  if (entity != null) { 
   InputStream inputStream = null; 
   try { 
    inputStream = entity.getContent(); 
    final Bitmap bitmap = BitmapFactory.decodeStream(inputStream); 
    return bitmap; 
   } finally { 
    if (inputStream != null) { 
     inputStream.close(); 
    } 
    entity.consumeContent(); 
   } 
  } 
 } catch (Exception e) { 
   getRequest.abort(); 
  Log.e("android123Debug", "Error while retrieving bitmap from " + url, e.toString()); 
 } finally { 
  if (client != null) { 
   client.close(); 
  } 
 } 
 return null; 
}

static class FlushedInputStream extends FilterInputStream { 
 public FlushedInputStream(InputStream inputStream) { 
  super(inputStream); 
 } 

 @Override 
 public long skip(long n) throws IOException { 
  long totalBytesSkipped = 0L; 
  while (totalBytesSkipped < n) { 
   long bytesSkipped = in.skip(n - totalBytesSkipped); 
   if (bytesSkipped == 0L) { 
     int byte = read(); 
     if (byte < 0) { 
      break; // we reached EOF 
     } else { 
      bytesSkipped = 1; // we read one byte 
     } 
   } 
   totalBytesSkipped += bytesSkipped; 
  } 
  return totalBytesSkipped; 
 } 
} 

 public class ImageDownloader { 

 public void download(String url, ImageView imageView) { 
   BitmapDownloaderTask task = new BitmapDownloaderTask(imageView); 
   task.execute(url); 
  } 
 } 

} 

class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> { 
 private String url; 
 private final WeakReference<ImageView> imageViewReference; //使用WeakReference解决内存问题 

 public BitmapDownloaderTask(ImageView imageView) { 
  imageViewReference = new WeakReference<ImageView>(imageView); 
 } 

 @Override 
 protected Bitmap doInBackground(String... params) { //实际的下载线程，内部其实是concurrent线程，所以不会阻塞 
 
   return downloadBitmap(params[0]); 

 } 

 @Override 
  protected void onPostExecute(Bitmap bitmap) { //下载完后执行的 
  if (isCancelled()) { 
   bitmap = null; 
  } 

  if (imageViewReference != null) { 
   ImageView imageView = imageViewReference.get(); 
   if (imageView != null) { 
    imageView.setImageBitmap(bitmap); //下载完设置imageview为刚才下载的bitmap对象 
   } 
  } 
 } 
}