按塊讀取和寫入文件塊

Question

我正在開發一個文件加密程序。 我使用下面的 function 加密文件，直到我意識到它不適合大文件； 因為它將所有文件內容讀入 memory。 現在，我需要創建一個可以分塊讀寫文件內容的 function。 我怎樣才能做到這一點？

private fun encryptFile(file: File) {
   val originalData = file.readBytes()
   val encryptData = encrypt(originalData)
   encryptData?.run {
       file.writeBytes(this)
   }
}

Answer 1

您的加密 function 顯然不能保持這種狀態。 它必須成為一個包裝 InputStream 或 OutputStream 的東西，然后它就相當簡單了。

請注意，手動加密幾乎 100% 保證您會搞砸，而且加密流已經存在。 你有什么理由重新發明輪子並注冊通過重新發明你不應該做的事情來破壞安全性？

Answer 2

看看代碼。 OP

    // ...
StringBuilder sb = new StringBuilder(); 
String line;
while ((line = inputStream.readLine()) != null) {
    sb.append(line);

    // if enough content is read, extract the chunk
    while (sb.length() >= chunkSize) {

        String c = sb.substring(0, chunkSize);
        // do something with the string

        // add the remaining content to the next chunk
        sb = new StringBuilder(sb.substring(chunkSize));
    }
}
// thats the last chunk
String c = sb.toString();
// do something with the string

編輯：如何使用 Chilkat 庫鏈接下載 Chilkat 庫

加密文件塊的代碼示例

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {

CkCrypt2 crypt = new CkCrypt2();

crypt.put_CryptAlgorithm("aes");
crypt.put_CipherMode("cbc");
crypt.put_KeyLength(128);

crypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F","hex");
crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex");

String fileToEncrypt = "qa_data/hamlet.xml";
CkFileAccess facIn = new CkFileAccess();
boolean success = facIn.OpenForRead(fileToEncrypt);
if (success != true) {
    System.out.println("Failed to open file that is to be encrytped.");
    return;
    }

String outputEncryptedFile = "qa_output/hamlet.enc";
CkFileAccess facOutEnc = new CkFileAccess();
success = facOutEnc.OpenForWrite(outputEncryptedFile);
if (success != true) {
    System.out.println("Failed to encrypted output file.");
    return;
    }

// Let's encrypt in 10000 byte chunks.
int chunkSize = 10000;
int numChunks = facIn.GetNumBlocks(chunkSize);

crypt.put_FirstChunk(true);
crypt.put_LastChunk(false);

CkBinData bd = new CkBinData();

int i = 0;
while (i < numChunks) {
    i = i+1;
    if (i == numChunks) {
        crypt.put_LastChunk(true);
        }

    // Read the next chunk from the file.
    // The last chunk will be whatever amount remains in the file..
    bd.Clear();
    facIn.FileReadBd(chunkSize,bd);

    // Encrypt.
    crypt.EncryptBd(bd);

    // Write the encrypted chunk to the output file.
    facOutEnc.FileWriteBd(bd,0,0);

    crypt.put_FirstChunk(false);
    }

// Make sure both FirstChunk and LastChunk are restored to true after
// encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
// will produce unexpected results.
crypt.put_FirstChunk(true);
crypt.put_LastChunk(true);

facIn.FileClose();
facOutEnc.FileClose();

// Decrypt the encrypted output file in a single call using CBC mode:
String decryptedFile = "qa_output/hamlet_dec.xml";
success = crypt.CkDecryptFile(outputEncryptedFile,decryptedFile);
// Assume success for the example..

// Compare the contents of the decrypted file with the original file:
boolean bSame = facIn.FileContentsEqual(fileToEncrypt,decryptedFile);
System.out.println("bSame = " + bSame);
  }
}