通过图片地址获取图片，优化

 // Get the source image's dimensions
  BitmapFactory.Options options = new BitmapFactory.Options();
  // This does not download the actual image, just downloads headers.
  options.inJustDecodeBounds = true; 
  BitmapFactory.decodeFile(IMAGE_FILE_URL, options);
  // The actual width of the image.
  int srcWidth = options.outWidth;  
  // The actual height of the image.
  int srcHeight = options.outHeight;  

  // Only scale if the source is bigger than the width of the destination view.
  if(desiredWidth > srcWidth)
    desiredWidth = srcWidth;

  // Calculate the correct inSampleSize/scale value. This helps reduce memory use. It should be a power of 2.
  int inSampleSize = 1;
  while(srcWidth / 2 > desiredWidth){
    srcWidth /= 2;
    srcHeight /= 2;
    inSampleSize *= 2;
  }

  float desiredScale = (float) desiredWidth / srcWidth;

  // Decode with inSampleSize
  options.inJustDecodeBounds = false;
  options.inDither = false;
  options.inSampleSize = inSampleSize;
  options.inScaled = false;
  // Ensures the image stays as a 32-bit ARGB_8888 image.
  // This preserves image quality.
  options.inPreferredConfig = Bitmap.Config.ARGB_8888;  
                                                	
  Bitmap sampledSrcBitmap = BitmapFactory.decodeFile(IMAGE_FILE_URL, options);

  // Resize
  Matrix matrix = new Matrix();
  matrix.postScale(desiredScale, desiredScale);
  Bitmap scaledBitmap = Bitmap.createBitmap(sampledSrcBitmap, 0, 0,
      sampledSrcBitmap.getWidth(), sampledSrcBitmap.getHeight(), matrix, true);
  sampledSrcBitmap = null;

  // Save
  FileOutputStream out = new FileOutputStream(LOCAL_PATH_TO_STORE_IMAGE);
  scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 100, out);
  scaledBitmap = null;