FileChannel 加密

要对 FileChannel 进行加密，你可以使用 Java 的加密工具来实现。以下是一个简单的示例代码，演示了如何使用 AES 加密算法对文件进行加密和解密。

import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

public class FileEncryption {
    private static final String ALGORITHM = "AES";
    private static final String TRANSFORMATION = "AES/ECB/PKCS5Padding";

    // 生成密钥
    private static SecretKey generateKey(String encryptionKey) throws NoSuchAlgorithmException {
        return new SecretKeySpec(encryptionKey.getBytes(), ALGORITHM);
    }

    // 加密文件
    public static void encryptFile(String sourceFilePath, String destinationFilePath, String encryptionKey)
            throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
        SecretKey secretKey = generateKey(encryptionKey);

        Cipher cipher = Cipher.getInstance(TRANSFORMATION);
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);

        try (FileInputStream inputStream = new FileInputStream(sourceFilePath);
             FileOutputStream outputStream = new FileOutputStream(destinationFilePath);
             FileChannel inputChannel = inputStream.getChannel();
             FileChannel outputChannel = outputStream.getChannel()) {

            ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
            while (inputChannel.read(buffer) != -1) {
                buffer.flip();
                byte[] bytes = new byte[buffer.limit()];
                buffer.get(bytes);

                byte[] encryptedBytes = cipher.update(bytes);
                outputChannel.write(ByteBuffer.wrap(encryptedBytes));

                buffer.clear();
            }

            byte[] finalEncryptedBytes = cipher.doFinal();
            outputChannel.write(ByteBuffer.wrap(finalEncryptedBytes));
        } catch (IOException | ShortBufferException | IllegalBlockSizeException | BadPaddingException e) {
            e.printStackTrace();
            throw new IOException("Error encrypting file", e);
        }
    }

    // 解密文件
    public static void decryptFile(String sourceFilePath, String destinationFilePath, String encryptionKey)
            throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
        SecretKey secretKey = generateKey(encryptionKey);

        Cipher cipher = Cipher.getInstance(TRANSFORMATION);
        cipher.init(Cipher.DECRYPT_MODE, secretKey);

        try (FileInputStream inputStream = new FileInputStream(sourceFilePath);
             FileOutputStream outputStream = new FileOutputStream(destinationFilePath);
             FileChannel inputChannel = inputStream.getChannel();
             FileChannel outputChannel = outputStream.getChannel()) {

            ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
            while (inputChannel.read(buffer) != -1) {
                buffer.flip();
                byte[] bytes = new byte[buffer.limit()];
                buffer.get(bytes);

                byte[] decryptedBytes = cipher.update(bytes);
                outputChannel.write(ByteBuffer.wrap(decryptedBytes));

                buffer.clear();
            }

            byte[] finalDecryptedBytes = cipher.doFinal();
            outputChannel.write(ByteBuffer.wrap(finalDecryptedBytes));
        } catch (IOException | ShortBufferException | IllegalBlockSizeException | BadPaddingException e) {
            e.printStackTrace();
            throw new IOException("Error decrypting file", e);
        }
    }

    public static void main(String[] args) {
        String sourceFilePath = "path/to/source/file";
        String encryptedFilePath = "path/to/encrypted/file";
        String decryptedFilePath = "path/to/decrypted/file";
        String encryptionKey = "yourEncryptionKey";

        try {
            encryptFile(sourceFilePath, encryptedFilePath, encryptionKey);
            decryptFile(encryptedFilePath, decryptedFilePath, encryptionKey);
        } catch (IOException | NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException e) {
            e.printStackTrace();
        }
    }
}

在上述示例代码中，你需要用实际的文件路径替换 `sourceFilePath`、`encryptedFilePath` 和 `decryptedFilePath` 的占位符，并设置一个用于加密和解密的密钥 `encryptionKey`。该代码使用 AES 算法和 ECB 模式进行加密和解密。请注意，ECB 模式在某些情况下可能存在安全隐患，因此你可以选择其他更安全的模式，例如 CBC 模式。

该示例使用了 Java 的 NIO 文件通道（FileChannel）来读取和写入文件数据。加密和解密过程通过对文件数据进行分块处理，每次处理一个缓冲区（ByteBuffer），并将加密或解密后的数据写入输出文件。

请确保在使用此代码时仔细阅读并理解其中的逻辑，并根据自己的需求进行适当的修改和优化。