如何使用文件输入和输出流从一个文件中添加和获取特定数量的字节数？

Question

我正在处理一个类来加密/解密大文件，所以我尝试使用流而不是字节数组来避免OutOfMemory异常。在加密方法中，我将随机salt和iv添加到加密文件的开头，它工作得很好，下面是代码:

public File encryptFile(File inputFile, File outPutFile, String password, ProgressBar progressBar, Label progressPercentage){
        //Create IV
        byte[] ivBytes = new byte[16];
        SecureRandom random1 = new SecureRandom();
        random1.nextBytes(ivBytes);
        IvParameterSpec iv = new IvParameterSpec(ivBytes);


        //Create the key with the salt
        SecureRandom random = new SecureRandom();
        byte[] salt = new byte[SALT_SIZE];
        random.nextBytes(salt);

        SecretKeySpec keySpec = generateAesKey(password, salt);

        //Create and Init the cipher
        Cipher c = Cipher.getInstance("AES/CBC/"+padding);
        c.init(Cipher.ENCRYPT_MODE, keySpec, iv);

        byte[] buf = new byte[8192];
        FileInputStream in = new FileInputStream(inputFile);
        FileOutputStream out = new FileOutputStream(outPutFile);
        int nread;
        int progress = 0;

        byte[] ivAndSalt = new byte[ivBytes.length + salt.length];
        System.arraycopy(ivBytes,0, ivAndSalt,0, ivBytes.length );
        System.arraycopy(salt, 0, ivAndSalt, ivBytes.length, salt.length);
        out.write(ivAndSalt);

        while((nread = in.read(buf)) != -1) {
            byte[] enc = c.update(buf, 0, nread);
            out.write(enc);
            progress++;
        }

然后尝试在解密方法中获取iv和salt，然后使用FileInputStream.GetChannel.Position():
将文件的其余部分解密为输出文件

 public File decryptFile(File inputFile, File outPutFile, String password, ProgressBar progressBar, Label progressPercentage) {
        //Create and Init Cipher
        Cipher c = Cipher.getInstance("AES/CBC/" + padding);

        FileInputStream in = new FileInputStream(inputFile);
        FileOutputStream out = new FileOutputStream(outPutFile);

        //Getting the iv and salt
        byte[] ivBytes = new byte[16];
        byte[] salt = new byte[SALT_SIZE];
        byte[] ivAndSalt = new byte[ivBytes.length+SALT_SIZE];
        in.read(ivAndSalt, 0, ivBytes.length+SALT_SIZE);
        System.arraycopy(ivAndSalt, 0, ivBytes, 0, ivBytes.length);
        System.arraycopy(ivAndSalt, ivBytes.length, salt, 0, SALT_SIZE);
        IvParameterSpec iv =new IvParameterSpec(ivBytes);
        SecretKeySpec keySpec = generateAesKey(password, salt);
        c.init(Cipher.DECRYPT_MODE, keySpec, iv);


        in.getChannel().position(ivAndSalt.length);

        int nread;
        int progress = 0;
        byte[] buf = new byte[8192];

        while((nread = in.read(buf)) != -1) {
                byte[] enc = c.update(buf, 0, nread);
                out.write(enc);
                progress++;

            /*if (enc.length / 8192 != 0)
                    System.out.println((nread*progress) + "%");*/
        }
        System.out.println("Size of out before doFinal(): " + out.getChannel().size());
        byte[] enc = c.doFinal();
        out.write(enc);
        System.out.println("Size of out after doFinal(): " + out.getChannel().size());
        return  outPutFile;
    } 

我在调用decryptFile（）时没有遇到错误，但是生成的文件已损坏，这意味着解密过程中的某个地方存在问题。

Answer 1

这个问题完全是一个愚蠢的问题，在dofinal()并将enc字节数组写入输出后，我忘记关闭输入和输出流：

in.close();
out.close();