取樣加密的圖像需要很多時間Android

Question

我以滑動方式在imageView中顯示圖像，大約需要122〜160 ms，但是當我加密圖像並解密然後顯示它時，大約需要600 - 900 ms

什麼讓我困惑的是，時間不解密的時候，它是圖像採樣時間

Ciphered 

imgInput = new FileInputStream(imageFile); 

        startTime = System.currentTimeMillis(); 
        CipherInputStream cs = getCipherStream(imgInput); 
        endTime = System.currentTimeMillis(); 

        Log.i(TAG,"Ciphered: "+ (endTime - startTime)); 

        startTime = System.currentTimeMillis(); 
        //decode ciphered 
        bmp = ImagingUtils.decodeSampledBitmapFromResourceMemOpt(cs, 800, 
          800); 
        endTime = System.currentTimeMillis(); 

        Log.i(TAG,"Decoding ciphered: "+ (endTime - startTime)); 

        imageView.setImageBitmap(bmp); 

unChiphered

imgInput = new FileInputStream(imageFile); 

        startTime = System.currentTimeMillis(); 
        //decode non-ciphereed 
        bmp = ImagingUtils.decodeSampledBitmapFromResourceMemOpt(imgInput, 800, 
          800); 
        endTime = System.currentTimeMillis(); 

        Log.i(TAG,"decoding unciphered: "+ (endTime - startTime)); 

        imageView.setImageBitmap(bmp); 

解碼程序代碼（推薦在另一篇文章在計算器）

byte[] byteArr = new byte[0]; 
     byte[] buffer = new byte[1024]; 
     int len; 
     int count = 0; 

     try { 
      while ((len = inputStream.read(buffer)) > -1) { 
       if (len != 0) { 
        if (count + len > byteArr.length) { 
         byte[] newbuf = new byte[(count + len) * 2]; 
         System.arraycopy(byteArr, 0, newbuf, 0, count); 
         byteArr = newbuf; 
        } 

        System.arraycopy(buffer, 0, byteArr, count, len); 
        count += len; 
       } 
      } 

      final BitmapFactory.Options options = new BitmapFactory.Options(); 
      options.inJustDecodeBounds = true; 
      BitmapFactory.decodeByteArray(byteArr, 0, count, options); 

      options.inSampleSize = calculateInSampleSize(options, reqWidth, 
        reqHeight); 
      options.inPurgeable = true; 
      options.inInputShareable = true; 
      options.inJustDecodeBounds = false; 
      options.inPreferredConfig = Bitmap.Config.ARGB_8888; 

      int[] pids = { android.os.Process.myPid() }; 

      // MemoryInfo myMemInfo = mAM.getProcessMemoryInfo(pids)[0]; 
      // Log.e(TAG, "dalvikPss (decoding) = " + myMemInfo.dalvikPss); 

      return BitmapFactory.decodeByteArray(byteArr, 0, count, options); 

我用解密

public CipherInputStream getCipherStream(InputStream imageis) throws Throwable 
    { 

     // Open the input stream 
     InputStream is = this.getAssets().open("inserva.key"); 

     Cipher c = new EncryptonUtils(is).getCipher(Cipher.DECRYPT_MODE); //cipher.init(mode,secretKey,paramSpec); 


     CipherInputStream cis = new CipherInputStream(imageis, c); 

     return cis ; 
    } 

Answer 1

我猜的方法將讀取時間。密碼流在內存中，文件流不在。 YOu可能通過從磁盤讀取小塊來製作太多的光盤訪問命令。嘗試將FileInputStream包裝在BufferedReader中，看看它是否改善了事情。

我確實看到你一次只讀1K，但這樣做效率不高 - 磁盤上最小可讀單元的大小至少爲4K，可能是8K或更多，因此，重新讀取相同的數據多次。